[PATCH RFC v6 02/21] dept: Implement Dept(Dependency Tracker)

[Byungchul Park <byungchul.park@xxxxxxx>]

CURRENT STATUS
--------------
Lockdep tracks acquisition order of locks in order to detect deadlock,
and IRQ and IRQ enable/disable state as well to take accident
acquisitions into account.

Lockdep should be turned off once it detects and reports a deadlock
since the data structure and algorithm are not reusable after detection
because of the complex design.

PROBLEM
-------
*Waits* and their *events* that never reach eventually cause deadlock.
However, Lockdep is only interested in lock acquisition order, forcing
to emulate lock acqusition even for just waits and events that have
nothing to do with real lock.

Even worse, no one likes Lockdep's false positive detection because that
prevents further one that might be more valuable. That's why all the
kernel developers are sensitive to Lockdep's false positive.

Besides those, by tracking acquisition order, it cannot correctly deal
with read lock and cross-event e.g. wait_for_completion()/complete() for
deadlock detection. Lockdep is no longer a good tool for that purpose.

SOLUTION
--------
Again, *waits* and their *events* that never reach eventually cause
deadlock. The new solution, Dept(DEPendency Tracker), focuses on waits
and events themselves. Dept tracks waits and events and report it if
any event would be never reachable.

Dept does:
   . Works with read lock in the right way.
   . Works with any wait and event e.i. cross-event.
   . Continue to work even after reporting multiple times.
   . Provides simple and intuitive APIs.
   . Does exactly what dependency checker should do.

Q & A
-----
Q. Is this the first try ever to address the problem?
A. No. Cross-release feature (b09be676e0ff2 locking/lockdep: Implement
   the 'crossrelease' feature) addressed it 2 years ago that was a
   Lockdep extension and merged but reverted shortly because:

   Cross-release started to report valuable hidden problems but started
   to give report false positive reports as well. For sure, no one
   likes Lockdep's false positive reports since it makes Lockdep stop,
   preventing reporting further real problems.

Q. Why not Dept was developed as an extension of Lockdep?
A. Lockdep definitely includes all the efforts great developers have
   made for a long time so as to be quite stable enough. But I had to
   design and implement newly because of the following:

   1) Lockdep was designed to track lock acquisition order. The APIs and
      implementation do not fit on wait-event model.
   2) Lockdep is turned off on detection including false positive. Which
      is terrible and prevents developing any extension for stronger
      detection.

Q. Do you intend to totally replace Lockdep?
A. No. Lockdep also checks if lock usage is correct. Of course, the
   dependency check routine should be replaced but the other functions
   should be still there.

Q. Do you mean the dependency check routine should be replaced right
   away?
A. No. I admit Lockdep is stable enough thanks to great efforts kernel
   developers have made. Lockdep and Dept, both should be in the kernel
   until Dept gets considered stable.

Q. Stronger detection capability would give more false positive report.
   Which was a big problem when cross-release was introduced. Is it ok
   with Dept?
A. It's ok. Dept allows multiple reporting thanks to simple and quite
   generalized design. Of course, false positive reports should be fixed
   anyway but it's no longer as a critical problem as it was.

Signed-off-by: Byungchul Park <byungchul.park@xxxxxxx>
---
 include/linux/dept.h            |  528 ++++++++
 include/linux/dept_sdt.h        |   60 +
 include/linux/hardirq.h         |    3 +
 include/linux/irqflags.h        |   71 +-
 include/linux/lockdep.h         |   61 +-
 include/linux/lockdep_types.h   |    3 +
 include/linux/sched.h           |    7 +
 init/init_task.c                |    2 +
 init/main.c                     |    2 +
 kernel/Makefile                 |    1 +
 kernel/dependency/Makefile      |    3 +
 kernel/dependency/dept.c        | 2633 +++++++++++++++++++++++++++++++++++++++
 kernel/dependency/dept_hash.h   |   10 +
 kernel/dependency/dept_object.h |   13 +
 kernel/exit.c                   |    1 +
 kernel/fork.c                   |    2 +
 kernel/locking/lockdep.c        |   28 +-
 kernel/module.c                 |    2 +
 kernel/sched/core.c             |    8 +
 lib/Kconfig.debug               |   27 +
 20 files changed, 3433 insertions(+), 32 deletions(-)
 create mode 100644 include/linux/dept.h
 create mode 100644 include/linux/dept_sdt.h
 create mode 100644 kernel/dependency/Makefile
 create mode 100644 kernel/dependency/dept.c
 create mode 100644 kernel/dependency/dept_hash.h
 create mode 100644 kernel/dependency/dept_object.h

diff --git a/include/linux/dept.h b/include/linux/dept.h
new file mode 100644
index 00000000..c498060
--- /dev/null
+++ b/include/linux/dept.h
@@ -0,0 +1,528 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * DEPT(DEPendency Tracker) - runtime dependency tracker
+ *
+ * Started by Byungchul Park <max.byungchul.park@xxxxxxxxx>:
+ *
+ *  Copyright (c) 2020 LG Electronics, Inc., Byungchul Park
+ */
+
+#ifndef __LINUX_DEPT_H
+#define __LINUX_DEPT_H
+
+#ifdef CONFIG_DEPT
+
+#include <linux/types.h>
+
+struct task_struct;
+
+#define DEPT_MAX_STACK_ENTRY		16
+#define DEPT_MAX_WAIT_HIST		64
+#define DEPT_MAX_ECXT_HELD		48
+
+#define DEPT_MAX_SUBCLASSES		16
+#define DEPT_MAX_SUBCLASSES_EVT		2
+#define DEPT_MAX_SUBCLASSES_USR		(DEPT_MAX_SUBCLASSES / DEPT_MAX_SUBCLASSES_EVT)
+#define DEPT_MAX_SUBCLASSES_CACHE	2
+
+#define DEPT_SIRQ			0
+#define DEPT_HIRQ			1
+#define DEPT_IRQS_NR			2
+#define DEPT_SIRQF			(1UL << DEPT_SIRQ)
+#define DEPT_HIRQF			(1UL << DEPT_HIRQ)
+
+struct dept_ecxt;
+struct dept_iecxt {
+	struct dept_ecxt		*ecxt;
+	int				enirq;
+	/*
+	 * for preventing to add a new ecxt
+	 */
+	bool				staled;
+};
+
+struct dept_wait;
+struct dept_iwait {
+	struct dept_wait		*wait;
+	int				irq;
+	/*
+	 * for preventing to add a new wait
+	 */
+	bool				staled;
+	bool				touched;
+};
+
+struct dept_class {
+	union {
+		struct llist_node	pool_node;
+
+		/*
+		 * reference counter for object management
+		 */
+		atomic_t		ref;
+	};
+
+	/*
+	 * unique information about the class
+	 */
+	const char			*name;
+	unsigned long			key;
+	int				sub;
+
+	/*
+	 * for BFS
+	 */
+	unsigned int			bfs_gen;
+	int				bfs_dist;
+	struct dept_class		*bfs_parent;
+
+	/*
+	 * for hashing this object
+	 */
+	struct hlist_node		hash_node;
+
+	/*
+	 * for linking all classes
+	 */
+	struct list_head		all_node;
+
+	/*
+	 * for associating its dependencies
+	 */
+	struct list_head		dep_head;
+	struct list_head		dep_rev_head;
+
+	/*
+	 * for tracking IRQ dependencies
+	 */
+	struct dept_iecxt		iecxt[DEPT_IRQS_NR];
+	struct dept_iwait		iwait[DEPT_IRQS_NR];
+};
+
+struct dept_stack {
+	union {
+		struct llist_node	pool_node;
+
+		/*
+		 * reference counter for object management
+		 */
+		atomic_t		ref;
+	};
+
+	/*
+	 * backtrace entries
+	 */
+	unsigned long			raw[DEPT_MAX_STACK_ENTRY];
+	int nr;
+};
+
+struct dept_ecxt {
+	union {
+		struct llist_node	pool_node;
+
+		/*
+		 * reference counter for object management
+		 */
+		atomic_t		ref;
+	};
+
+	/*
+	 * function that entered to this ecxt
+	 */
+	const char			*ecxt_fn;
+
+	/*
+	 * event function
+	 */
+	const char			*event_fn;
+
+	/*
+	 * associated class
+	 */
+	struct dept_class		*class;
+
+	/*
+	 * flag indicating which IRQ has been
+	 * enabled within the event context
+	 */
+	unsigned long			enirqf;
+
+	/*
+	 * where the IRQ-enabled happened
+	 */
+	unsigned long			enirq_ip[DEPT_IRQS_NR];
+	struct dept_stack		*enirq_stack[DEPT_IRQS_NR];
+
+	/*
+	 * where the event context started
+	 */
+	unsigned long			ecxt_ip;
+	struct dept_stack		*ecxt_stack;
+
+	/*
+	 * where the event triggered
+	 */
+	unsigned long			event_ip;
+	struct dept_stack		*event_stack;
+};
+
+struct dept_wait {
+	union {
+		struct llist_node	pool_node;
+
+		/*
+		 * reference counter for object management
+		 */
+		atomic_t		ref;
+	};
+
+	/*
+	 * function causing this wait
+	 */
+	const char			*wait_fn;
+
+	/*
+	 * the associated class
+	 */
+	struct dept_class		*class;
+
+	/*
+	 * which IRQ the wait was placed in
+	 */
+	unsigned long			irqf;
+
+	/*
+	 * where the IRQ wait happened
+	 */
+	unsigned long			irq_ip[DEPT_IRQS_NR];
+	struct dept_stack		*irq_stack[DEPT_IRQS_NR];
+
+	/*
+	 * where the wait happened
+	 */
+	unsigned long			wait_ip;
+	struct dept_stack		*wait_stack;
+};
+
+struct dept_dep {
+	union {
+		struct llist_node	pool_node;
+
+		/*
+		 * reference counter for object management
+		 */
+		atomic_t		ref;
+	};
+
+	/*
+	 * key data of dependency
+	 */
+	struct dept_ecxt		*ecxt;
+	struct dept_wait		*wait;
+
+	/*
+	 * This object can be referred without dept_lock
+	 * held but with IRQ disabled, e.g. for hash
+	 * lookup. So deferred deletion is needed.
+	 */
+	struct rcu_head			rh;
+
+	/*
+	 * for BFS
+	 */
+	struct list_head		bfs_node;
+
+	/*
+	 * for hashing this object
+	 */
+	struct hlist_node		hash_node;
+
+	/*
+	 * for linking to a class object
+	 */
+	struct list_head		dep_node;
+	struct list_head		dep_rev_node;
+};
+
+struct dept_hash {
+	/*
+	 * hash table
+	 */
+	struct hlist_head		*table;
+
+	/*
+	 * size of the table e.i. 2^bits
+	 */
+	int				bits;
+};
+
+struct dept_pool {
+	const char			*name;
+
+	/*
+	 * object size
+	 */
+	size_t				obj_sz;
+
+	/*
+	 * the number of the static array
+	 */
+	atomic_t			obj_nr;
+
+	/*
+	 * offset of ->pool_node
+	 */
+	size_t				node_off;
+
+	/*
+	 * pointer to the pool
+	 */
+	void				*spool;
+	struct llist_head		boot_pool;
+	struct llist_head __percpu	*lpool;
+};
+
+struct dept_ecxt_held {
+	/*
+	 * associated event context
+	 */
+	struct dept_ecxt		*ecxt;
+
+	/*
+	 * unique key for this dept_ecxt_held
+	 */
+	unsigned long			key;
+
+	/*
+	 * the wgen when the event context started
+	 */
+	unsigned int			wgen;
+
+	/*
+	 * for allowing user aware nesting
+	 */
+	int				nest;
+};
+
+struct dept_wait_hist {
+	/*
+	 * associated wait
+	 */
+	struct dept_wait		*wait;
+
+	/*
+	 * unique id of all waits system-wise until wrapped
+	 */
+	unsigned int			wgen;
+
+	/*
+	 * local context id to identify IRQ context
+	 */
+	unsigned int			ctxt_id;
+};
+
+struct dept_key {
+	union {
+		/*
+		 * Each byte-wise address will be used as its key.
+		 */
+		char			subkeys[DEPT_MAX_SUBCLASSES];
+
+		/*
+		 * for caching the main class pointer
+		 */
+		struct dept_class	*classes[DEPT_MAX_SUBCLASSES_CACHE];
+	};
+};
+
+struct dept_map {
+	const char			*name;
+	struct dept_key			*keys;
+	int				sub_usr;
+
+	/*
+	 * It's local copy for fast acces to the associated classes. And
+	 * Also used for dept_key instance for statically defined map.
+	 */
+	struct dept_key			keys_local;
+
+	/*
+	 * wait timestamp associated to this map
+	 */
+	unsigned int			wgen;
+
+	/*
+	 * whether this map should be going to be checked or not
+	 */
+	bool				nocheck;
+};
+
+#define DEPT_MAP_INITIALIZER(n)						\
+{									\
+	.name = #n,							\
+	.keys = NULL,							\
+	.sub_usr = 0,							\
+	.keys_local = { .classes = { 0 } },				\
+	.wgen = 0U,							\
+	.nocheck = false,						\
+}
+
+struct dept_task {
+	/*
+	 * all event contexts that have entered and before exiting
+	 */
+	struct dept_ecxt_held		ecxt_held[DEPT_MAX_ECXT_HELD];
+	int				ecxt_held_pos;
+
+	/*
+	 * ring buffer holding all waits that have happened
+	 */
+	struct dept_wait_hist		wait_hist[DEPT_MAX_WAIT_HIST];
+	int				wait_hist_pos;
+
+	/*
+	 * sequential id to identify each IRQ context
+	 */
+	unsigned int			irq_id[DEPT_IRQS_NR];
+
+	/*
+	 * for tracking IRQ-enabled points with cross-event
+	 */
+	unsigned int			wgen_enirq[DEPT_IRQS_NR];
+
+	/*
+	 * for keeping up-to-date IRQ-enabled points
+	 */
+	unsigned long			enirq_ip[DEPT_IRQS_NR];
+
+	/*
+	 * current effective IRQ-enabled flag
+	 */
+	unsigned long			eff_enirqf;
+
+	/*
+	 * for reserving a current stack instance at each operation
+	 */
+	struct dept_stack		*stack;
+
+	/*
+	 * for preventing recursive call into DEPT engine
+	 */
+	int				recursive;
+
+	/*
+	 * for staging data to commit a wait
+	 */
+	struct dept_map			*stage_m;
+	unsigned long			stage_w_f;
+	const char			*stage_w_fn;
+	int				stage_ne;
+
+	/*
+	 * the number of missing ecxts
+	 */
+	int				missing_ecxt;
+
+	/*
+	 * for tracking IRQ-enable state
+	 */
+	bool				hardirqs_enabled;
+	bool				softirqs_enabled;
+};
+
+#define DEPT_TASK_INITIALIZER(t)				\
+{								\
+	.wait_hist = { { .wait = NULL, } },			\
+	.ecxt_held_pos = 0,					\
+	.wait_hist_pos = 0,					\
+	.irq_id = { 0U },					\
+	.wgen_enirq = { 0U },					\
+	.enirq_ip = { 0UL },					\
+	.eff_enirqf = 0UL,					\
+	.stack = NULL,						\
+	.recursive = 0,						\
+	.stage_m = NULL,					\
+	.stage_w_f = 0UL,					\
+	.stage_w_fn = NULL,					\
+	.stage_ne = 0,						\
+	.missing_ecxt = 0,					\
+	.hardirqs_enabled = false,				\
+	.softirqs_enabled = false,				\
+}
+
+extern void dept_on(void);
+extern void dept_off(void);
+extern void dept_init(void);
+extern void dept_task_init(struct task_struct *t);
+extern void dept_task_exit(struct task_struct *t);
+extern void dept_free_range(void *start, unsigned int sz);
+extern void dept_map_init(struct dept_map *m, struct dept_key *k, int sub, const char *n);
+extern void dept_map_reinit(struct dept_map *m);
+extern void dept_map_nocheck(struct dept_map *m);
+
+extern void dept_wait(struct dept_map *m, unsigned long w_f, unsigned long ip, const char *w_fn, int ne);
+extern void dept_stage_wait(struct dept_map *m, unsigned long w_f, const char *w_fn, int ne);
+extern void dept_ask_event_wait_commit(unsigned long ip);
+extern void dept_clean_stage(void);
+extern void dept_ecxt_enter(struct dept_map *m, unsigned long e_f, unsigned long ip, const char *c_fn, const char *e_fn, int ne);
+extern void dept_ask_event(struct dept_map *m);
+extern void dept_event(struct dept_map *m, unsigned long e_f, unsigned long ip, const char *e_fn);
+extern void dept_ecxt_exit(struct dept_map *m, unsigned long e_f, unsigned long ip);
+
+static inline void dept_ecxt_enter_nokeep(struct dept_map *m)
+{
+	dept_ecxt_enter(m, 0UL, 0UL, NULL, NULL, 0);
+}
+
+/*
+ * for users who want to manage external keys
+ */
+extern void dept_key_init(struct dept_key *k);
+extern void dept_key_destroy(struct dept_key *k);
+
+extern void dept_softirq_enter(void);
+extern void dept_hardirq_enter(void);
+extern void dept_aware_softirqs_enable(void);
+extern void dept_aware_hardirqs_enable(void);
+extern void dept_aware_softirqs_disable(void);
+extern void dept_aware_hardirqs_disable(void);
+extern void dept_enirq_transition(unsigned long ip);
+#else /* !CONFIG_DEPT */
+struct dept_key  { };
+struct dept_map  { };
+struct dept_task { };
+
+#define DEPT_MAP_INITIALIZER(n) { }
+#define DEPT_TASK_INITIALIZER(t) { }
+
+#define dept_on()				do { } while (0)
+#define dept_off()				do { } while (0)
+#define dept_init()				do { } while (0)
+#define dept_task_init(t)			do { } while (0)
+#define dept_task_exit(t)			do { } while (0)
+#define dept_free_range(s, sz)			do { } while (0)
+#define dept_map_init(m, k, s, n)		do { (void)(n); (void)(k); } while (0)
+#define dept_map_reinit(m)			do { } while (0)
+#define dept_map_nocheck(m)			do { } while (0)
+
+#define dept_wait(m, w_f, ip, w_fn, ne)		do { (void)(w_fn); } while (0)
+#define dept_stage_wait(m, w_f, w_fn, ne)	do { (void)(w_fn); } while (0)
+#define dept_ask_event_wait_commit(ip)		do { } while (0)
+#define dept_clean_stage()			do { } while (0)
+#define dept_ecxt_enter(m, e_f, ip, c_fn, e_fn, ne) do { (void)(c_fn); (void)(e_fn); } while (0)
+#define dept_ask_event(m)			do { } while (0)
+#define dept_event(m, e_f, ip, e_fn)		do { (void)(e_fn); } while (0)
+#define dept_ecxt_exit(m, e_f, ip)		do { } while (0)
+#define dept_ecxt_enter_nokeep(m)		do { } while (0)
+#define dept_key_init(k)			do { (void)(k); } while (0)
+#define dept_key_destroy(k)			do { (void)(k); } while (0)
+
+#define dept_softirq_enter()				do { } while (0)
+#define dept_hardirq_enter()				do { } while (0)
+#define dept_aware_softirqs_enable()			do { } while (0)
+#define dept_aware_hardirqs_enable()			do { } while (0)
+#define dept_aware_softirqs_disable()			do { } while (0)
+#define dept_aware_hardirqs_disable()			do { } while (0)
+#define dept_enirq_transition(ip)			do { } while (0)
+#endif
+#endif /* __LINUX_DEPT_H */
diff --git a/include/linux/dept_sdt.h b/include/linux/dept_sdt.h
new file mode 100644
index 00000000..49763cd
--- /dev/null
+++ b/include/linux/dept_sdt.h
@@ -0,0 +1,60 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Dept Single-event Dependency Tracker
+ *
+ * Started by Byungchul Park <max.byungchul.park@xxxxxxxxx>:
+ *
+ *  Copyright (c) 2020 LG Electronics, Inc., Byungchul Park
+ */
+
+#ifndef __LINUX_DEPT_SDT_H
+#define __LINUX_DEPT_SDT_H
+
+#include <linux/dept.h>
+
+#ifdef CONFIG_DEPT
+/*
+ * SDT(Single-event Dependency Tracker) APIs
+ *
+ * In case that one dept_map instance maps to a single event, SDT APIs
+ * can be used.
+ */
+#define sdt_map_init(m)							\
+	do {								\
+		static struct dept_key __key;				\
+		dept_map_init(m, &__key, 0, #m);			\
+	} while (0)
+#define sdt_map_init_key(m, k)		dept_map_init(m, k, 0, #m)
+
+#define sdt_wait(m)							\
+	do {								\
+		dept_ask_event(m);					\
+		dept_wait(m, 1UL, _THIS_IP_, "wait", 0);		\
+	} while (0)
+/*
+ * This will be committed in __schedule() when it actually gets to
+ * __schedule(). Both dept_ask_event() and dept_wait() will be performed
+ * on the commit in __schedule().
+ */
+#define sdt_wait_prepare(m)		dept_stage_wait(m, 1UL, "wait", 0)
+#define sdt_wait_finish()		dept_clean_stage()
+#define sdt_ecxt_enter(m)		dept_ecxt_enter(m, 1UL, _THIS_IP_, "start", "event", 0)
+#define sdt_event(m)			dept_event(m, 1UL, _THIS_IP_, "event")
+#define sdt_ecxt_exit(m)		dept_ecxt_exit(m, 1UL, _THIS_IP_)
+#else /* !CONFIG_DEPT */
+#define DEPT_SDT_MAP_INIT(dname)	{ }
+
+#define sdt_map_init(m)			do { } while (0)
+#define sdt_map_init_key(m, k)		do { (void)(k); } while (0)
+#define sdt_wait(m)			do { } while (0)
+#define sdt_wait_prepare(m)		do { } while (0)
+#define sdt_wait_finish()		do { } while (0)
+#define sdt_ecxt_enter(m)		do { } while (0)
+#define sdt_event(m)			do { } while (0)
+#define sdt_ecxt_exit(m)		do { } while (0)
+#endif
+
+#define DEFINE_DEPT_SDT(x)		\
+	struct dept_map x = DEPT_MAP_INITIALIZER(x)
+
+#endif /* __LINUX_DEPT_SDT_H */
diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
index 76878b3..07005f2 100644
--- a/include/linux/hardirq.h
+++ b/include/linux/hardirq.h
@@ -5,6 +5,7 @@
 #include <linux/context_tracking_state.h>
 #include <linux/preempt.h>
 #include <linux/lockdep.h>
+#include <linux/dept.h>
 #include <linux/ftrace_irq.h>
 #include <linux/sched.h>
 #include <linux/vtime.h>
@@ -114,6 +115,7 @@ static inline void rcu_nmi_exit(void) { }
  */
 #define __nmi_enter()						\
 	do {							\
+		dept_off();					\
 		lockdep_off();					\
 		arch_nmi_enter();				\
 		BUG_ON(in_nmi() == NMI_MASK);			\
@@ -136,6 +138,7 @@ static inline void rcu_nmi_exit(void) { }
 		__preempt_count_sub(NMI_OFFSET + HARDIRQ_OFFSET);	\
 		arch_nmi_exit();				\
 		lockdep_on();					\
+		dept_on();					\
 	} while (0)
 
 #define nmi_exit()						\
diff --git a/include/linux/irqflags.h b/include/linux/irqflags.h
index 4b14093..d168fa3 100644
--- a/include/linux/irqflags.h
+++ b/include/linux/irqflags.h
@@ -13,23 +13,52 @@
 #define _LINUX_TRACE_IRQFLAGS_H
 
 #include <linux/typecheck.h>
+#include <linux/dept.h>
 #include <asm/irqflags.h>
 #include <asm/percpu.h>
 
 /* Currently lockdep_softirqs_on/off is used only by lockdep */
 #ifdef CONFIG_PROVE_LOCKING
-  extern void lockdep_softirqs_on(unsigned long ip);
-  extern void lockdep_softirqs_off(unsigned long ip);
-  extern void lockdep_hardirqs_on_prepare(unsigned long ip);
-  extern void lockdep_hardirqs_on(unsigned long ip);
-  extern void lockdep_hardirqs_off(unsigned long ip);
+  extern void __lockdep_softirqs_on(unsigned long ip);
+  extern void __lockdep_softirqs_off(unsigned long ip);
+  extern void __lockdep_hardirqs_on_prepare(unsigned long ip);
+  extern void __lockdep_hardirqs_on(unsigned long ip);
+  extern void __lockdep_hardirqs_off(unsigned long ip);
 #else
-  static inline void lockdep_softirqs_on(unsigned long ip) { }
-  static inline void lockdep_softirqs_off(unsigned long ip) { }
-  static inline void lockdep_hardirqs_on_prepare(unsigned long ip) { }
-  static inline void lockdep_hardirqs_on(unsigned long ip) { }
-  static inline void lockdep_hardirqs_off(unsigned long ip) { }
+  static inline void __lockdep_softirqs_on(unsigned long ip) { }
+  static inline void __lockdep_softirqs_off(unsigned long ip) { }
+  static inline void __lockdep_hardirqs_on_prepare(unsigned long ip) { }
+  static inline void __lockdep_hardirqs_on(unsigned long ip) { }
+  static inline void __lockdep_hardirqs_off(unsigned long ip) { }
 #endif
+static inline void lockdep_softirqs_on(unsigned long ip)
+{
+	__lockdep_softirqs_on(ip);
+	dept_aware_softirqs_enable();
+	dept_enirq_transition(ip);
+}
+static inline void lockdep_softirqs_off(unsigned long ip)
+{
+	__lockdep_softirqs_off(ip);
+	dept_aware_softirqs_disable();
+	dept_enirq_transition(ip);
+}
+static inline void lockdep_hardirqs_on_prepare(unsigned long ip)
+{
+	__lockdep_hardirqs_on_prepare(ip);
+	dept_aware_hardirqs_enable();
+	dept_enirq_transition(ip);
+}
+static inline void lockdep_hardirqs_on(unsigned long ip)
+{
+	__lockdep_hardirqs_on(ip);
+}
+static inline void lockdep_hardirqs_off(unsigned long ip)
+{
+	__lockdep_hardirqs_off(ip);
+	dept_aware_hardirqs_disable();
+	dept_enirq_transition(ip);
+}
 
 #ifdef CONFIG_TRACE_IRQFLAGS
 
@@ -60,8 +89,10 @@ struct irqtrace_events {
 # define lockdep_softirqs_enabled(p)	((p)->softirqs_enabled)
 # define lockdep_hardirq_enter()			\
 do {							\
-	if (__this_cpu_inc_return(hardirq_context) == 1)\
+	if (__this_cpu_inc_return(hardirq_context) == 1) {\
 		current->hardirq_threaded = 0;		\
+		dept_hardirq_enter();			\
+	}						\
 } while (0)
 # define lockdep_hardirq_threaded()		\
 do {						\
@@ -135,7 +166,8 @@ struct irqtrace_events {
 #if defined(CONFIG_TRACE_IRQFLAGS) && !defined(CONFIG_PREEMPT_RT)
 # define lockdep_softirq_enter()		\
 do {						\
-	current->softirq_context++;		\
+	if (!current->softirq_context++)	\
+		dept_softirq_enter();		\
 } while (0)
 # define lockdep_softirq_exit()			\
 do {						\
@@ -170,17 +202,28 @@ struct irqtrace_events {
 /*
  * Wrap the arch provided IRQ routines to provide appropriate checks.
  */
-#define raw_local_irq_disable()		arch_local_irq_disable()
-#define raw_local_irq_enable()		arch_local_irq_enable()
+#define raw_local_irq_disable()				\
+	do {						\
+		arch_local_irq_disable();		\
+		dept_aware_hardirqs_disable();		\
+	} while (0)
+#define raw_local_irq_enable()				\
+	do {						\
+		dept_aware_hardirqs_enable();		\
+		arch_local_irq_enable();		\
+	} while (0)
 #define raw_local_irq_save(flags)			\
 	do {						\
 		typecheck(unsigned long, flags);	\
 		flags = arch_local_irq_save();		\
+		dept_aware_hardirqs_disable();		\
 	} while (0)
 #define raw_local_irq_restore(flags)			\
 	do {						\
 		typecheck(unsigned long, flags);	\
 		raw_check_bogus_irq_restore();		\
+		if (!arch_irqs_disabled_flags(flags))	\
+			dept_aware_hardirqs_enable();	\
 		arch_local_irq_restore(flags);		\
 	} while (0)
 #define raw_local_save_flags(flags)			\
diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 467b942..aee4660 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -20,6 +20,33 @@
 extern int prove_locking;
 extern int lock_stat;
 
+#ifdef CONFIG_DEPT
+static inline void dept_after_copy_map(struct dept_map *to,
+				       struct dept_map *from)
+{
+	int i;
+
+	if (from->keys == &from->keys_local)
+		to->keys = &to->keys_local;
+
+	if (!to->keys)
+		return;
+
+	/*
+	 * Since the class cache can be modified concurrently we could observe
+	 * half pointers (64bit arch using 32bit copy insns). Therefore clear
+	 * the caches and take the performance hit.
+	 *
+	 * XXX it doesn't work well with lockdep_set_class_and_subclass(), since
+	 *     that relies on cache abuse.
+	 */
+	for (i = 0; i < DEPT_MAX_SUBCLASSES_CACHE; i++)
+		to->keys->classes[i] = NULL;
+}
+#else
+#define dept_after_copy_map(t, f)	do { } while (0)
+#endif
+
 #ifdef CONFIG_LOCKDEP
 
 #include <linux/linkage.h>
@@ -43,6 +70,8 @@ static inline void lockdep_copy_map(struct lockdep_map *to,
 	 */
 	for (i = 0; i < NR_LOCKDEP_CACHING_CLASSES; i++)
 		to->class_cache[i] = NULL;
+
+	dept_after_copy_map(&to->dmap, &from->dmap);
 }
 
 /*
@@ -176,8 +205,19 @@ struct held_lock {
 	current->lockdep_recursion -= LOCKDEP_OFF;	\
 } while (0)
 
-extern void lockdep_register_key(struct lock_class_key *key);
-extern void lockdep_unregister_key(struct lock_class_key *key);
+extern void __lockdep_register_key(struct lock_class_key *key);
+extern void __lockdep_unregister_key(struct lock_class_key *key);
+
+#define lockdep_register_key(k)				\
+do {							\
+	__lockdep_register_key(k);			\
+	dept_key_init(&(k)->dkey);			\
+} while (0)
+#define lockdep_unregister_key(k)			\
+do {							\
+	__lockdep_unregister_key(k);			\
+	dept_key_destroy(&(k)->dkey);			\
+} while (0)
 
 /*
  * These methods are used by specific locking variants (spinlocks,
@@ -185,9 +225,18 @@ struct held_lock {
  * to lockdep:
  */
 
-extern void lockdep_init_map_type(struct lockdep_map *lock, const char *name,
+extern void __lockdep_init_map_type(struct lockdep_map *lock, const char *name,
 	struct lock_class_key *key, int subclass, u8 inner, u8 outer, u8 lock_type);
 
+#define lockdep_init_map_type(l, n, k, s, i, o, t)		\
+do {								\
+	__lockdep_init_map_type(l, n, k, s, i, o, t);		\
+	if ((k) == &__lockdep_no_validate__)			\
+		dept_map_nocheck(&(l)->dmap);			\
+	else							\
+		dept_map_init(&(l)->dmap, &(k)->dkey, s, n);	\
+} while (0)
+
 static inline void
 lockdep_init_map_waits(struct lockdep_map *lock, const char *name,
 		       struct lock_class_key *key, int subclass, u8 inner, u8 outer)
@@ -435,9 +484,13 @@ enum xhlock_context_t {
 /*
  * To initialize a lockdep_map statically use this macro.
  * Note that _name must not be NULL.
+ *
+ * TODO: I found the case to use an address of other than a real key as
+ * _key, for instance, in workqueue. We cannot use it as key in Dept.
  */
 #define STATIC_LOCKDEP_MAP_INIT(_name, _key) \
-	{ .name = (_name), .key = (void *)(_key), }
+	{ .name = (_name), .key = (void *)(_key), \
+	  .dmap = DEPT_MAP_INITIALIZER(_name) }
 
 static inline void lockdep_invariant_state(bool force) {}
 static inline void lockdep_free_task(struct task_struct *task) {}
diff --git a/include/linux/lockdep_types.h b/include/linux/lockdep_types.h
index d224308..50c8879 100644
--- a/include/linux/lockdep_types.h
+++ b/include/linux/lockdep_types.h
@@ -11,6 +11,7 @@
 #define __LINUX_LOCKDEP_TYPES_H
 
 #include <linux/types.h>
+#include <linux/dept.h>
 
 #define MAX_LOCKDEP_SUBCLASSES		8UL
 
@@ -76,6 +77,7 @@ struct lock_class_key {
 		struct hlist_node		hash_entry;
 		struct lockdep_subclass_key	subkeys[MAX_LOCKDEP_SUBCLASSES];
 	};
+	struct dept_key				dkey;
 };
 
 extern struct lock_class_key __lockdep_no_validate__;
@@ -185,6 +187,7 @@ struct lockdep_map {
 	int				cpu;
 	unsigned long			ip;
 #endif
+	struct dept_map			dmap;
 };
 
 struct pin_cookie { unsigned int val; };
diff --git a/include/linux/sched.h b/include/linux/sched.h
index d5e3c00..3716e41 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -35,6 +35,7 @@
 #include <linux/seqlock.h>
 #include <linux/kcsan.h>
 #include <asm/kmap_size.h>
+#include <linux/dept.h>
 
 /* task_struct member predeclarations (sorted alphabetically): */
 struct audit_context;
@@ -201,12 +202,16 @@
  */
 #define __set_current_state(state_value)				\
 	do {								\
+		if (state_value == TASK_RUNNING)			\
+			dept_clean_stage();				\
 		debug_normal_state_change((state_value));		\
 		WRITE_ONCE(current->__state, (state_value));		\
 	} while (0)
 
 #define set_current_state(state_value)					\
 	do {								\
+		if (state_value == TASK_RUNNING)			\
+			dept_clean_stage();				\
 		debug_normal_state_change((state_value));		\
 		smp_store_mb(current->__state, (state_value));		\
 	} while (0)
@@ -1156,6 +1161,8 @@ struct task_struct {
 	struct held_lock		held_locks[MAX_LOCK_DEPTH];
 #endif
 
+	struct dept_task		dept_task;
+
 #if defined(CONFIG_UBSAN) && !defined(CONFIG_UBSAN_TRAP)
 	unsigned int			in_ubsan;
 #endif
diff --git a/init/init_task.c b/init/init_task.c
index 73cc8f0..ceea035 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -12,6 +12,7 @@
 #include <linux/audit.h>
 #include <linux/numa.h>
 #include <linux/scs.h>
+#include <linux/dept.h>
 
 #include <linux/uaccess.h>
 
@@ -193,6 +194,7 @@ struct task_struct init_task
 	.curr_chain_key = INITIAL_CHAIN_KEY,
 	.lockdep_recursion = 0,
 #endif
+	.dept_task = DEPT_TASK_INITIALIZER(init_task),
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 	.ret_stack		= NULL,
 	.tracing_graph_pause	= ATOMIC_INIT(0),
diff --git a/init/main.c b/init/main.c
index 98182c3..deabdd5 100644
--- a/init/main.c
+++ b/init/main.c
@@ -65,6 +65,7 @@
 #include <linux/debug_locks.h>
 #include <linux/debugobjects.h>
 #include <linux/lockdep.h>
+#include <linux/dept.h>
 #include <linux/kmemleak.h>
 #include <linux/padata.h>
 #include <linux/pid_namespace.h>
@@ -1071,6 +1072,7 @@ asmlinkage __visible void __init __no_sanitize_address start_kernel(void)
 		      panic_param);
 
 	lockdep_init();
+	dept_init();
 
 	/*
 	 * Need to run this when irqs are enabled, because it wants
diff --git a/kernel/Makefile b/kernel/Makefile
index 847a82b..5de01e2 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -53,6 +53,7 @@ obj-y += rcu/
 obj-y += livepatch/
 obj-y += dma/
 obj-y += entry/
+obj-y += dependency/
 
 obj-$(CONFIG_KCMP) += kcmp.o
 obj-$(CONFIG_FREEZER) += freezer.o
diff --git a/kernel/dependency/Makefile b/kernel/dependency/Makefile
new file mode 100644
index 00000000..b5cfb8a
--- /dev/null
+++ b/kernel/dependency/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0
+
+obj-$(CONFIG_DEPT) += dept.o
diff --git a/kernel/dependency/dept.c b/kernel/dependency/dept.c
new file mode 100644
index 00000000..1e90284
--- /dev/null
+++ b/kernel/dependency/dept.c
@@ -0,0 +1,2633 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * DEPT(DEPendency Tracker) - Runtime dependency tracker
+ *
+ * Started by Byungchul Park <max.byungchul.park@xxxxxxxxx>:
+ *
+ *  Copyright (c) 2020 LG Electronics, Inc., Byungchul Park
+ *
+ * DEPT provides a general way to detect deadlock possibility in runtime
+ * and the interest is not limited to typical lock but to every
+ * syncronization primitives.
+ *
+ * The following ideas were borrowed from LOCKDEP:
+ *
+ *    1) Use a graph to track relationship between classes.
+ *    2) Prevent performance regression using hash.
+ *
+ * The following items were enhanced from LOCKDEP:
+ *
+ *    1) Cover more deadlock cases.
+ *    2) Allow muliple reports.
+ *
+ * TODO: Both LOCKDEP and DEPT should co-exist until DEPT is considered
+ * stable. Then the dependency check routine should be replaced with
+ * DEPT after. It should finally look like:
+ *
+ *
+ *
+ * As is:
+ *
+ *    LOCKDEP
+ *    +-----------------------------------------+
+ *    | Lock usage correctness check            | <-> locks
+ *    |                                         |
+ *    |                                         |
+ *    | +-------------------------------------+ |
+ *    | | Dependency check                    | |
+ *    | | (by tracking lock acquisition order)| |
+ *    | +-------------------------------------+ |
+ *    |                                         |
+ *    +-----------------------------------------+
+ *
+ *    DEPT
+ *    +-----------------------------------------+
+ *    | Dependency check                        | <-> waits/events
+ *    | (by tracking wait and event context)    |
+ *    +-----------------------------------------+
+ *
+ *
+ *
+ * To be:
+ *
+ *    LOCKDEP
+ *    +-----------------------------------------+
+ *    | Lock usage correctness check            | <-> locks
+ *    |                                         |
+ *    |                                         |
+ *    |       (Request dependency check)        |
+ *    |                    T                    |
+ *    +--------------------|--------------------+
+ *                         |
+ *    DEPT                 V
+ *    +-----------------------------------------+
+ *    | Dependency check                        | <-> waits/events
+ *    | (by tracking wait and event context)    |
+ *    +-----------------------------------------+
+ */
+
+#include <linux/sched.h>
+#include <linux/stacktrace.h>
+#include <linux/spinlock.h>
+#include <linux/kallsyms.h>
+#include <linux/hash.h>
+#include <linux/dept.h>
+#include <linux/utsname.h>
+
+static int dept_stop;
+static int dept_per_cpu_ready;
+
+#define DEPT_READY_WARN (!oops_in_progress)
+
+/*
+ * Make all operations using DEPT_WARN_ON() fail on oops_in_progress and
+ * prevent warning message.
+ */
+#define DEPT_WARN_ON_ONCE(c)						\
+	({								\
+		int __ret = 0;						\
+									\
+		if (likely(DEPT_READY_WARN))				\
+			__ret = WARN_ONCE(c, "DEPT_WARN_ON_ONCE: " #c);	\
+		__ret;							\
+	})
+
+#define DEPT_WARN_ONCE(s...)						\
+	({								\
+		if (likely(DEPT_READY_WARN))				\
+			WARN_ONCE(1, "DEPT_WARN_ONCE: " s);		\
+	})
+
+#define DEPT_WARN_ON(c)							\
+	({								\
+		int __ret = 0;						\
+									\
+		if (likely(DEPT_READY_WARN))				\
+			__ret = WARN(c, "DEPT_WARN_ON: " #c);		\
+		__ret;							\
+	})
+
+#define DEPT_WARN(s...)							\
+	({								\
+		if (likely(DEPT_READY_WARN))				\
+			WARN(1, "DEPT_WARN: " s);			\
+	})
+
+#define DEPT_STOP(s...)							\
+	({								\
+		WRITE_ONCE(dept_stop, 1);				\
+		if (likely(DEPT_READY_WARN))				\
+			WARN(1, "DEPT_STOP: " s);			\
+	})
+
+#define DEPT_INFO_ONCE(s...) pr_warn_once("DEPT_INFO_ONCE: " s)
+
+static arch_spinlock_t dept_spin = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
+
+/*
+ * DEPT internal engine should be careful in using outside functions
+ * e.g. printk at reporting since that kind of usage might cause
+ * untrackable deadlock.
+ */
+static atomic_t dept_outworld = ATOMIC_INIT(0);
+
+static inline void dept_outworld_enter(void)
+{
+	atomic_inc(&dept_outworld);
+}
+
+static inline void dept_outworld_exit(void)
+{
+	atomic_dec(&dept_outworld);
+}
+
+static inline bool dept_outworld_entered(void)
+{
+	return atomic_read(&dept_outworld);
+}
+
+static inline bool dept_lock(void)
+{
+	while (!arch_spin_trylock(&dept_spin))
+		if (unlikely(dept_outworld_entered()))
+			return false;
+	return true;
+}
+
+static inline void dept_unlock(void)
+{
+	arch_spin_unlock(&dept_spin);
+}
+
+/*
+ * whether to stack-trace on every wait or every ecxt
+ */
+static bool rich_stack = true;
+
+enum bfs_ret {
+	BFS_CONTINUE,
+	BFS_CONTINUE_REV,
+	BFS_DONE,
+	BFS_SKIP,
+};
+
+static inline bool before(unsigned int a, unsigned int b)
+{
+	return (int)(a - b) < 0;
+}
+
+static inline bool valid_stack(struct dept_stack *s)
+{
+	return s && s->nr > 0;
+}
+
+static inline bool valid_class(struct dept_class *c)
+{
+	return c->key;
+}
+
+static inline void inval_class(struct dept_class *c)
+{
+	c->key = 0UL;
+}
+
+static inline struct dept_ecxt *dep_e(struct dept_dep *d)
+{
+	return d->ecxt;
+}
+
+static inline struct dept_wait *dep_w(struct dept_dep *d)
+{
+	return d->wait;
+}
+
+static inline struct dept_class *dep_fc(struct dept_dep *d)
+{
+	return dep_e(d)->class;
+}
+
+static inline struct dept_class *dep_tc(struct dept_dep *d)
+{
+	return dep_w(d)->class;
+}
+
+static inline const char *irq_str(int irq)
+{
+	if (irq == DEPT_SIRQ)
+		return "softirq";
+	if (irq == DEPT_HIRQ)
+		return "hardirq";
+	return "(unknown)";
+}
+
+static inline struct dept_task *dept_task(void)
+{
+	return &current->dept_task;
+}
+
+/*
+ * Pool
+ * =====================================================================
+ * DEPT maintains pools to provide objects in a safe way.
+ *
+ *    1) Static pool is used at the beginning of booting time.
+ *    2) Local pool is tried first before the static pool. Objects that
+ *       have been freed will be placed.
+ */
+
+enum object_t {
+#define OBJECT(id, nr) OBJECT_##id,
+	#include "dept_object.h"
+#undef  OBJECT
+	OBJECT_NR,
+};
+
+#define OBJECT(id, nr)							\
+static struct dept_##id spool_##id[nr];					\
+static DEFINE_PER_CPU(struct llist_head, lpool_##id);
+	#include "dept_object.h"
+#undef  OBJECT
+
+static struct dept_pool pool[OBJECT_NR] = {
+#define OBJECT(id, nr) {						\
+	.name = #id,							\
+	.obj_sz = sizeof(struct dept_##id),				\
+	.obj_nr = ATOMIC_INIT(nr),					\
+	.node_off = offsetof(struct dept_##id, pool_node),		\
+	.spool = spool_##id,						\
+	.lpool = &lpool_##id, },
+	#include "dept_object.h"
+#undef  OBJECT
+};
+
+/*
+ * Can use llist no matter whether CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG is
+ * enabled or not because NMI and other contexts in the same CPU never
+ * run inside of DEPT concurrently by preventing reentrance.
+ */
+static void *from_pool(enum object_t t)
+{
+	struct dept_pool *p;
+	struct llist_head *h;
+	struct llist_node *n;
+
+	/*
+	 * llist_del_first() doesn't allow concurrent access e.g.
+	 * between process and IRQ context.
+	 */
+	if (DEPT_WARN_ON(!irqs_disabled()))
+		return NULL;
+
+	p = &pool[t];
+
+	/*
+	 * Try local pool first.
+	 */
+	if (likely(dept_per_cpu_ready))
+		h = this_cpu_ptr(p->lpool);
+	else
+		h = &p->boot_pool;
+
+	n = llist_del_first(h);
+	if (n)
+		return (void *)n - p->node_off;
+
+	/*
+	 * Try static pool.
+	 */
+	if (atomic_read(&p->obj_nr) > 0) {
+		int idx = atomic_dec_return(&p->obj_nr);
+
+		if (idx >= 0)
+			return p->spool + (idx * p->obj_sz);
+	}
+
+	DEPT_INFO_ONCE("Pool(%s) is empty.\n", p->name);
+	return NULL;
+}
+
+static void to_pool(void *o, enum object_t t)
+{
+	struct dept_pool *p = &pool[t];
+	struct llist_head *h;
+
+	preempt_disable();
+	if (likely(dept_per_cpu_ready))
+		h = this_cpu_ptr(p->lpool);
+	else
+		h = &p->boot_pool;
+
+	llist_add(o + p->node_off, h);
+	preempt_enable();
+}
+
+#define OBJECT(id, nr)							\
+static void (*ctor_##id)(struct dept_##id *a);				\
+static void (*dtor_##id)(struct dept_##id *a);				\
+static inline struct dept_##id *new_##id(void)				\
+{									\
+	struct dept_##id *a;						\
+									\
+	a = (struct dept_##id *)from_pool(OBJECT_##id);			\
+	if (unlikely(!a))						\
+		return NULL;						\
+									\
+	atomic_set(&a->ref, 1);						\
+									\
+	if (ctor_##id)							\
+		ctor_##id(a);						\
+									\
+	return a;							\
+}									\
+									\
+static inline struct dept_##id *get_##id(struct dept_##id *a)		\
+{									\
+	atomic_inc(&a->ref);						\
+	return a;							\
+}									\
+									\
+static inline void put_##id(struct dept_##id *a)			\
+{									\
+	if (!atomic_dec_return(&a->ref)) {				\
+		if (dtor_##id)						\
+			dtor_##id(a);					\
+		to_pool(a, OBJECT_##id);				\
+	}								\
+}									\
+									\
+static inline void del_##id(struct dept_##id *a)			\
+{									\
+	put_##id(a);							\
+}									\
+									\
+static inline bool id##_consumed(struct dept_##id *a)			\
+{									\
+	return a && atomic_read(&a->ref) > 1;				\
+}
+#include "dept_object.h"
+#undef  OBJECT
+
+#define SET_CONSTRUCTOR(id, f) \
+static void (*ctor_##id)(struct dept_##id *a) = f
+
+static void initialize_dep(struct dept_dep *d)
+{
+	INIT_LIST_HEAD(&d->bfs_node);
+	INIT_LIST_HEAD(&d->dep_node);
+	INIT_LIST_HEAD(&d->dep_rev_node);
+}
+SET_CONSTRUCTOR(dep, initialize_dep);
+
+static void initialize_class(struct dept_class *c)
+{
+	int i;
+
+	for (i = 0; i < DEPT_IRQS_NR; i++) {
+		struct dept_iecxt *ie = &c->iecxt[i];
+		struct dept_iwait *iw = &c->iwait[i];
+
+		ie->ecxt = NULL;
+		ie->enirq = i;
+		ie->staled = false;
+
+		iw->wait = NULL;
+		iw->irq = i;
+		iw->staled = false;
+		iw->touched = false;
+	}
+	c->bfs_gen = 0U;
+
+	INIT_LIST_HEAD(&c->all_node);
+	INIT_LIST_HEAD(&c->dep_head);
+	INIT_LIST_HEAD(&c->dep_rev_head);
+}
+SET_CONSTRUCTOR(class, initialize_class);
+
+static void initialize_ecxt(struct dept_ecxt *e)
+{
+	int i;
+
+	for (i = 0; i < DEPT_IRQS_NR; i++) {
+		e->enirq_stack[i] = NULL;
+		e->enirq_ip[i] = 0UL;
+	}
+	e->ecxt_ip = 0UL;
+	e->ecxt_stack = NULL;
+	e->enirqf = 0UL;
+	e->event_ip = 0UL;
+	e->event_stack = NULL;
+}
+SET_CONSTRUCTOR(ecxt, initialize_ecxt);
+
+static void initialize_wait(struct dept_wait *w)
+{
+	int i;
+
+	for (i = 0; i < DEPT_IRQS_NR; i++) {
+		w->irq_stack[i] = NULL;
+		w->irq_ip[i] = 0UL;
+	}
+	w->wait_ip = 0UL;
+	w->wait_stack = NULL;
+	w->irqf = 0UL;
+}
+SET_CONSTRUCTOR(wait, initialize_wait);
+
+static void initialize_stack(struct dept_stack *s)
+{
+	s->nr = 0;
+}
+SET_CONSTRUCTOR(stack, initialize_stack);
+
+#define OBJECT(id, nr) \
+static void (*ctor_##id)(struct dept_##id *a);
+	#include "dept_object.h"
+#undef  OBJECT
+
+#undef  SET_CONSTRUCTOR
+
+#define SET_DESTRUCTOR(id, f) \
+static void (*dtor_##id)(struct dept_##id *a) = f
+
+static void destroy_dep(struct dept_dep *d)
+{
+	if (dep_e(d))
+		put_ecxt(dep_e(d));
+	if (dep_w(d))
+		put_wait(dep_w(d));
+}
+SET_DESTRUCTOR(dep, destroy_dep);
+
+static void destroy_ecxt(struct dept_ecxt *e)
+{
+	int i;
+
+	for (i = 0; i < DEPT_IRQS_NR; i++)
+		if (e->enirq_stack[i])
+			put_stack(e->enirq_stack[i]);
+	if (e->class)
+		put_class(e->class);
+	if (e->ecxt_stack)
+		put_stack(e->ecxt_stack);
+	if (e->event_stack)
+		put_stack(e->event_stack);
+}
+SET_DESTRUCTOR(ecxt, destroy_ecxt);
+
+static void destroy_wait(struct dept_wait *w)
+{
+	int i;
+
+	for (i = 0; i < DEPT_IRQS_NR; i++)
+		if (w->irq_stack[i])
+			put_stack(w->irq_stack[i]);
+	if (w->class)
+		put_class(w->class);
+	if (w->wait_stack)
+		put_stack(w->wait_stack);
+}
+SET_DESTRUCTOR(wait, destroy_wait);
+
+#define OBJECT(id, nr) \
+static void (*dtor_##id)(struct dept_##id *a);
+	#include "dept_object.h"
+#undef  OBJECT
+
+#undef  SET_DESTRUCTOR
+
+/*
+ * Caching and hashing
+ * =====================================================================
+ * DEPT makes use of caching and hashing to improve performance. Each
+ * object can be obtained in O(1) with its key.
+ *
+ * NOTE: Currently we assume all the objects in the hashs will never be
+ * removed. Implement it when needed.
+ */
+
+/*
+ * Some information might be lost but it's only for hashing key.
+ */
+static inline unsigned long mix(unsigned long a, unsigned long b)
+{
+	int halfbits = sizeof(unsigned long) * 8 / 2;
+	unsigned long halfmask = (1UL << halfbits) - 1UL;
+
+	return (a << halfbits) | (b & halfmask);
+}
+
+static bool cmp_dep(struct dept_dep *d1, struct dept_dep *d2)
+{
+	return dep_fc(d1)->key == dep_fc(d2)->key &&
+	       dep_tc(d1)->key == dep_tc(d2)->key;
+}
+
+static unsigned long key_dep(struct dept_dep *d)
+{
+	return mix(dep_fc(d)->key, dep_tc(d)->key);
+}
+
+static bool cmp_class(struct dept_class *c1, struct dept_class *c2)
+{
+	return c1->key == c2->key;
+}
+
+static unsigned long key_class(struct dept_class *c)
+{
+	return c->key;
+}
+
+#define HASH(id, bits)							\
+static struct hlist_head table_##id[1UL << bits];			\
+									\
+static inline struct hlist_head *head_##id(struct dept_##id *a)		\
+{									\
+	return table_##id + hash_long(key_##id(a), bits);		\
+}									\
+									\
+static inline struct dept_##id *hash_lookup_##id(struct dept_##id *a)	\
+{									\
+	struct dept_##id *b;						\
+									\
+	hlist_for_each_entry_rcu(b, head_##id(a), hash_node)		\
+		if (cmp_##id(a, b))					\
+			return b;					\
+	return NULL;							\
+}									\
+									\
+static inline void hash_add_##id(struct dept_##id *a)			\
+{									\
+	hlist_add_head_rcu(&a->hash_node, head_##id(a));		\
+}									\
+									\
+static inline void hash_del_##id(struct dept_##id *a)			\
+{									\
+	hlist_del_rcu(&a->hash_node);					\
+}
+#include "dept_hash.h"
+#undef  HASH
+
+static inline struct dept_dep *lookup_dep(struct dept_class *fc,
+					  struct dept_class *tc)
+{
+	struct dept_ecxt onetime_e = { .class = fc };
+	struct dept_wait onetime_w = { .class = tc };
+	struct dept_dep  onetime_d = { .ecxt = &onetime_e,
+				       .wait = &onetime_w };
+	return hash_lookup_dep(&onetime_d);
+}
+
+static inline struct dept_class *lookup_class(unsigned long key)
+{
+	struct dept_class onetime_c = { .key = key };
+
+	return hash_lookup_class(&onetime_c);
+}
+
+/*
+ * Report
+ * =====================================================================
+ * DEPT prints useful information to help debuging on detection of
+ * problematic dependency.
+ */
+
+static inline void print_ip_stack(unsigned long ip, struct dept_stack *s)
+{
+	if (ip)
+		print_ip_sym(KERN_WARNING, ip);
+
+	if (valid_stack(s)) {
+		pr_warn("stacktrace:\n");
+		stack_trace_print(s->raw, s->nr, 5);
+	}
+
+	if (!ip && !valid_stack(s))
+		pr_warn("(N/A)\n");
+}
+
+#define print_spc(spc, fmt, ...)					\
+	pr_warn("%*c" fmt, (spc) * 4, ' ', ##__VA_ARGS__)
+
+static void print_diagram(struct dept_dep *d)
+{
+	struct dept_ecxt *e = dep_e(d);
+	struct dept_wait *w = dep_w(d);
+	struct dept_class *fc = dep_fc(d);
+	struct dept_class *tc = dep_tc(d);
+	unsigned long irqf;
+	int irq;
+	bool firstline = true;
+	int spc = 1;
+	const char *w_fn = w->wait_fn  ?: "(unknown)";
+	const char *e_fn = e->event_fn ?: "(unknown)";
+	const char *c_fn = e->ecxt_fn ?: "(unknown)";
+
+	irqf = e->enirqf & w->irqf;
+	for_each_set_bit(irq, &irqf, DEPT_IRQS_NR) {
+		if (!firstline)
+			pr_warn("\nor\n\n");
+		firstline = false;
+
+		print_spc(spc, "[S] %s(%s:%d)\n", c_fn, fc->name, fc->sub);
+		print_spc(spc, "    <%s interrupt>\n", irq_str(irq));
+		print_spc(spc + 1, "[W] %s(%s:%d)\n", w_fn, tc->name, tc->sub);
+		print_spc(spc, "[E] %s(%s:%d)\n", e_fn, fc->name, fc->sub);
+	}
+
+	if (!irqf) {
+		print_spc(spc, "[S] %s(%s:%d)\n", c_fn, fc->name, fc->sub);
+		print_spc(spc, "[W] %s(%s:%d)\n", w_fn, tc->name, tc->sub);
+		print_spc(spc, "[E] %s(%s:%d)\n", e_fn, fc->name, fc->sub);
+	}
+}
+
+static void print_dep(struct dept_dep *d)
+{
+	struct dept_ecxt *e = dep_e(d);
+	struct dept_wait *w = dep_w(d);
+	struct dept_class *fc = dep_fc(d);
+	struct dept_class *tc = dep_tc(d);
+	unsigned long irqf;
+	int irq;
+	const char *w_fn = w->wait_fn  ?: "(unknown)";
+	const char *e_fn = e->event_fn ?: "(unknown)";
+	const char *c_fn = e->ecxt_fn ?: "(unknown)";
+
+	irqf = e->enirqf & w->irqf;
+	for_each_set_bit(irq, &irqf, DEPT_IRQS_NR) {
+		pr_warn("%s has been enabled:\n", irq_str(irq));
+		print_ip_stack(e->enirq_ip[irq], e->enirq_stack[irq]);
+		pr_warn("\n");
+
+		pr_warn("[S] %s(%s:%d):\n", c_fn, fc->name, fc->sub);
+		print_ip_stack(e->ecxt_ip, e->ecxt_stack);
+		pr_warn("\n");
+
+		pr_warn("[W] %s(%s:%d) in %s context:\n",
+		       w_fn, tc->name, tc->sub, irq_str(irq));
+		print_ip_stack(w->irq_ip[irq], w->irq_stack[irq]);
+		pr_warn("\n");
+
+		pr_warn("[E] %s(%s:%d):\n", e_fn, fc->name, fc->sub);
+		print_ip_stack(e->event_ip, e->event_stack);
+	}
+
+	if (!irqf) {
+		pr_warn("[S] %s(%s:%d):\n", c_fn, fc->name, fc->sub);
+		print_ip_stack(e->ecxt_ip, e->ecxt_stack);
+		pr_warn("\n");
+
+		pr_warn("[W] %s(%s:%d):\n", w_fn, tc->name, tc->sub);
+		print_ip_stack(w->wait_ip, w->wait_stack);
+		pr_warn("\n");
+
+		pr_warn("[E] %s(%s:%d):\n", e_fn, fc->name, fc->sub);
+		print_ip_stack(e->event_ip, e->event_stack);
+	}
+}
+
+static void save_current_stack(int skip);
+
+/*
+ * Print all classes in a circle.
+ */
+static void print_circle(struct dept_class *c)
+{
+	struct dept_class *fc = c->bfs_parent;
+	struct dept_class *tc = c;
+	int i;
+
+	dept_outworld_enter();
+	save_current_stack(6);
+
+	pr_warn("===================================================\n");
+	pr_warn("DEPT: Circular dependency has been detected.\n");
+	pr_warn("%s %.*s %s\n", init_utsname()->release,
+		(int)strcspn(init_utsname()->version, " "),
+		init_utsname()->version,
+		print_tainted());
+	pr_warn("---------------------------------------------------\n");
+	pr_warn("summary\n");
+	pr_warn("---------------------------------------------------\n");
+
+	if (fc == tc)
+		pr_warn("*** AA DEADLOCK ***\n\n");
+	else
+		pr_warn("*** DEADLOCK ***\n\n");
+
+	i = 0;
+	do {
+		struct dept_dep *d = lookup_dep(fc, tc);
+
+		pr_warn("context %c\n", 'A' + (i++));
+		print_diagram(d);
+		if (fc != c)
+			pr_warn("\n");
+
+		tc = fc;
+		fc = fc->bfs_parent;
+	} while (tc != c);
+
+	pr_warn("\n");
+	pr_warn("[S]: start of the event context\n");
+	pr_warn("[W]: the wait blocked\n");
+	pr_warn("[E]: the event not reachable\n");
+
+	i = 0;
+	do {
+		struct dept_dep *d = lookup_dep(fc, tc);
+
+		pr_warn("---------------------------------------------------\n");
+		pr_warn("context %c's detail\n", 'A' + i);
+		pr_warn("---------------------------------------------------\n");
+		pr_warn("context %c\n", 'A' + (i++));
+		print_diagram(d);
+		pr_warn("\n");
+		print_dep(d);
+
+		tc = fc;
+		fc = fc->bfs_parent;
+	} while (tc != c);
+
+	pr_warn("---------------------------------------------------\n");
+	pr_warn("information that might be helpful\n");
+	pr_warn("---------------------------------------------------\n");
+	dump_stack();
+
+	dept_outworld_exit();
+}
+
+/*
+ * BFS(Breadth First Search)
+ * =====================================================================
+ * Whenever a new dependency is added into the graph, search the graph
+ * for a new circular dependency.
+ */
+
+static inline void enqueue(struct list_head *h, struct dept_dep *d)
+{
+	list_add_tail(&d->bfs_node, h);
+}
+
+static inline struct dept_dep *dequeue(struct list_head *h)
+{
+	struct dept_dep *d;
+
+	d = list_first_entry(h, struct dept_dep, bfs_node);
+	list_del(&d->bfs_node);
+	return d;
+}
+
+static inline bool empty(struct list_head *h)
+{
+	return list_empty(h);
+}
+
+static void extend_queue(struct list_head *h, struct dept_class *cur)
+{
+	struct dept_dep *d;
+
+	list_for_each_entry(d, &cur->dep_head, dep_node) {
+		struct dept_class *next = dep_tc(d);
+
+		if (cur->bfs_gen == next->bfs_gen)
+			continue;
+		next->bfs_gen = cur->bfs_gen;
+		next->bfs_dist = cur->bfs_dist + 1;
+		next->bfs_parent = cur;
+		enqueue(h, d);
+	}
+}
+
+static void extend_queue_rev(struct list_head *h, struct dept_class *cur)
+{
+	struct dept_dep *d;
+
+	list_for_each_entry(d, &cur->dep_rev_head, dep_rev_node) {
+		struct dept_class *next = dep_fc(d);
+
+		if (cur->bfs_gen == next->bfs_gen)
+			continue;
+		next->bfs_gen = cur->bfs_gen;
+		next->bfs_dist = cur->bfs_dist + 1;
+		next->bfs_parent = cur;
+		enqueue(h, d);
+	}
+}
+
+typedef enum bfs_ret bfs_f(struct dept_dep *d, void *in, void **out);
+static unsigned int bfs_gen;
+
+/*
+ * NOTE: Must be called with dept_lock held.
+ */
+static void bfs(struct dept_class *c, bfs_f *cb, void *in, void **out)
+{
+	LIST_HEAD(q);
+	enum bfs_ret ret;
+
+	if (DEPT_WARN_ON(!cb))
+		return;
+
+	/*
+	 * Avoid zero bfs_gen.
+	 */
+	bfs_gen = bfs_gen + 1 ?: 1;
+
+	c->bfs_gen = bfs_gen;
+	c->bfs_dist = 0;
+	c->bfs_parent = c;
+
+	ret = cb(NULL, in, out);
+	if (ret == BFS_DONE)
+		return;
+	if (ret == BFS_SKIP)
+		return;
+	if (ret == BFS_CONTINUE)
+		extend_queue(&q, c);
+	if (ret == BFS_CONTINUE_REV)
+		extend_queue_rev(&q, c);
+
+	while (!empty(&q)) {
+		struct dept_dep *d = dequeue(&q);
+
+		ret = cb(d, in, out);
+		if (ret == BFS_DONE)
+			break;
+		if (ret == BFS_SKIP)
+			continue;
+		if (ret == BFS_CONTINUE)
+			extend_queue(&q, dep_tc(d));
+		if (ret == BFS_CONTINUE_REV)
+			extend_queue_rev(&q, dep_fc(d));
+	}
+
+	while (!empty(&q))
+		dequeue(&q);
+}
+
+/*
+ * Main operations
+ * =====================================================================
+ * Add dependencies - Each new dependency is added into the graph and
+ * checked if it forms a circular dependency.
+ *
+ * Track waits - Waits are queued into the ring buffer for later use to
+ * generate appropriate dependencies with cross-event.
+ *
+ * Track event contexts(ecxt) - Event contexts are pushed into local
+ * stack for later use to generate appropriate dependencies with waits.
+ */
+
+static inline unsigned long cur_enirqf(void);
+static inline int cur_irq(void);
+static inline unsigned int cur_ctxt_id(void);
+
+static inline struct dept_iecxt *iecxt(struct dept_class *c, int irq)
+{
+	return &c->iecxt[irq];
+}
+
+static inline struct dept_iwait *iwait(struct dept_class *c, int irq)
+{
+	return &c->iwait[irq];
+}
+
+static inline void stale_iecxt(struct dept_iecxt *ie)
+{
+	if (ie->ecxt)
+		put_ecxt(ie->ecxt);
+
+	WRITE_ONCE(ie->ecxt, NULL);
+	WRITE_ONCE(ie->staled, true);
+}
+
+static inline void set_iecxt(struct dept_iecxt *ie, struct dept_ecxt *e)
+{
+	/*
+	 * ->ecxt will never be updated once getting set until the class
+	 * gets removed.
+	 */
+	if (ie->ecxt)
+		DEPT_WARN_ON(1);
+	else
+		WRITE_ONCE(ie->ecxt, get_ecxt(e));
+}
+
+static inline void stale_iwait(struct dept_iwait *iw)
+{
+	if (iw->wait)
+		put_wait(iw->wait);
+
+	WRITE_ONCE(iw->wait, NULL);
+	WRITE_ONCE(iw->staled, true);
+}
+
+static inline void set_iwait(struct dept_iwait *iw, struct dept_wait *w)
+{
+	/*
+	 * ->wait will never be updated once getting set until the class
+	 * gets removed.
+	 */
+	if (iw->wait)
+		DEPT_WARN_ON(1);
+	else
+		WRITE_ONCE(iw->wait, get_wait(w));
+
+	iw->touched = true;
+}
+
+static inline void touch_iwait(struct dept_iwait *iw)
+{
+	iw->touched = true;
+}
+
+static inline void untouch_iwait(struct dept_iwait *iw)
+{
+	iw->touched = false;
+}
+
+static inline struct dept_stack *get_current_stack(void)
+{
+	struct dept_stack *s = dept_task()->stack;
+
+	return s ? get_stack(s) : NULL;
+}
+
+static inline void prepare_current_stack(void)
+{
+	struct dept_stack *s = dept_task()->stack;
+
+	/*
+	 * The dept_stack is already ready.
+	 */
+	if (s && !stack_consumed(s)) {
+		s->nr = 0;
+		return;
+	}
+
+	if (s)
+		put_stack(s);
+
+	s = dept_task()->stack = new_stack();
+	if (!s)
+		return;
+
+	get_stack(s);
+	del_stack(s);
+}
+
+static void save_current_stack(int skip)
+{
+	struct dept_stack *s = dept_task()->stack;
+
+	if (!s)
+		return;
+	if (valid_stack(s))
+		return;
+
+	s->nr = stack_trace_save(s->raw, DEPT_MAX_STACK_ENTRY, skip);
+}
+
+static void finish_current_stack(void)
+{
+	struct dept_stack *s = dept_task()->stack;
+
+	if (stack_consumed(s))
+		save_current_stack(2);
+}
+
+/*
+ * FIXME: For now, disable LOCKDEP while DEPT is working.
+ *
+ * Both LOCKDEP and DEPT report it on a deadlock detection using
+ * printk taking the risk of another deadlock that might be caused by
+ * locks of console or printk between inside and outside of them.
+ *
+ * For DEPT, it's no problem since multiple reports are allowed. But it
+ * would be a bad idea for LOCKDEP since it will stop even on a singe
+ * report. So we need to prevent LOCKDEP from its reporting the risk
+ * DEPT would take when reporting something.
+ */
+#include <linux/lockdep.h>
+
+void dept_off(void)
+{
+	dept_task()->recursive++;
+	lockdep_off();
+}
+
+void dept_on(void)
+{
+	dept_task()->recursive--;
+	lockdep_on();
+}
+
+static inline unsigned long dept_enter(void)
+{
+	unsigned long flags;
+
+	flags = arch_local_irq_save();
+	dept_off();
+	prepare_current_stack();
+	return flags;
+}
+
+static inline void dept_exit(unsigned long flags)
+{
+	finish_current_stack();
+	dept_on();
+	arch_local_irq_restore(flags);
+}
+
+static inline unsigned long dept_enter_recursive(void)
+{
+	unsigned long flags;
+
+	flags = arch_local_irq_save();
+	return flags;
+}
+
+static inline void dept_exit_recursive(unsigned long flags)
+{
+	arch_local_irq_restore(flags);
+}
+
+/*
+ * NOTE: Must be called with dept_lock held.
+ */
+static struct dept_dep *__add_dep(struct dept_ecxt *e,
+				  struct dept_wait *w)
+{
+	struct dept_dep *d;
+
+	if (!valid_class(e->class) || !valid_class(w->class))
+		return NULL;
+
+	if (lookup_dep(e->class, w->class))
+		return NULL;
+
+	d = new_dep();
+	if (unlikely(!d))
+		return NULL;
+
+	d->ecxt = get_ecxt(e);
+	d->wait = get_wait(w);
+
+	/*
+	 * Add the dependency into hash and graph.
+	 */
+	hash_add_dep(d);
+	list_add(&d->dep_node, &dep_fc(d)->dep_head);
+	list_add(&d->dep_rev_node, &dep_tc(d)->dep_rev_head);
+	return d;
+}
+
+static enum bfs_ret cb_check_dl(struct dept_dep *d,
+				void *in, void **out)
+{
+	struct dept_dep *new = (struct dept_dep *)in;
+
+	/*
+	 * initial condition for this BFS search
+	 */
+	if (!d) {
+		dep_tc(new)->bfs_parent = dep_fc(new);
+
+		if (dep_tc(new) != dep_fc(new))
+			return BFS_CONTINUE;
+
+		/*
+		 * AA circle does not make additional deadlock. We don't
+		 * have to continue this BFS search.
+		 */
+		print_circle(dep_tc(new));
+		return BFS_DONE;
+	}
+
+	/*
+	 * Allow multiple reports.
+	 */
+	if (dep_tc(d) == dep_fc(new))
+		print_circle(dep_tc(new));
+
+	return BFS_CONTINUE;
+}
+
+/*
+ * This function is actually in charge of reporting.
+ */
+static inline void check_dl_bfs(struct dept_dep *d)
+{
+	bfs(dep_tc(d), cb_check_dl, (void *)d, NULL);
+}
+
+static enum bfs_ret cb_find_iw(struct dept_dep *d, void *in, void **out)
+{
+	int irq = *(int *)in;
+	struct dept_class *fc;
+	struct dept_iwait *iw;
+
+	if (DEPT_WARN_ON(!out))
+		return BFS_DONE;
+
+	/*
+	 * initial condition for this BFS search
+	 */
+	if (!d)
+		return BFS_CONTINUE_REV;
+
+	fc = dep_fc(d);
+	iw = iwait(fc, irq);
+
+	/*
+	 * If any parent's ->wait was set, then the children would've
+	 * been touched.
+	 */
+	if (!iw->touched)
+		return BFS_SKIP;
+
+	if (!iw->wait)
+		return BFS_CONTINUE_REV;
+
+	*out = iw;
+	return BFS_DONE;
+}
+
+static struct dept_iwait *find_iw_bfs(struct dept_class *c, int irq)
+{
+	struct dept_iwait *iw = iwait(c, irq);
+	struct dept_iwait *found = NULL;
+
+	if (iw->wait)
+		return iw;
+
+	/*
+	 * '->touched == false' guarantees there's no parent that has
+	 * been set ->wait.
+	 */
+	if (!iw->touched)
+		return NULL;
+
+	bfs(c, cb_find_iw, (void *)&irq, (void **)&found);
+
+	if (found)
+		return found;
+
+	untouch_iwait(iw);
+	return NULL;
+}
+
+static enum bfs_ret cb_touch_iw_find_ie(struct dept_dep *d, void *in,
+					void **out)
+{
+	int irq = *(int *)in;
+	struct dept_class *tc;
+	struct dept_iecxt *ie;
+	struct dept_iwait *iw;
+
+	if (DEPT_WARN_ON(!out))
+		return BFS_DONE;
+
+	/*
+	 * initial condition for this BFS search
+	 */
+	if (!d)
+		return BFS_CONTINUE;
+
+	tc = dep_tc(d);
+	ie = iecxt(tc, irq);
+	iw = iwait(tc, irq);
+
+	touch_iwait(iw);
+
+	if (!ie->ecxt)
+		return BFS_CONTINUE;
+
+	if (!*out)
+		*out = ie;
+
+	return BFS_CONTINUE;
+}
+
+static struct dept_iecxt *touch_iw_find_ie_bfs(struct dept_class *c,
+					       int irq)
+{
+	struct dept_iecxt *ie = iecxt(c, irq);
+	struct dept_iwait *iw = iwait(c, irq);
+	struct dept_iecxt *found = ie->ecxt ? ie : NULL;
+
+	touch_iwait(iw);
+	bfs(c, cb_touch_iw_find_ie, (void *)&irq, (void **)&found);
+	return found;
+}
+
+/*
+ * Should be called with dept_lock held.
+ */
+static void __add_idep(struct dept_iecxt *ie, struct dept_iwait *iw)
+{
+	struct dept_dep *new;
+
+	/*
+	 * There's nothing to do.
+	 */
+	if (!ie || !iw || !ie->ecxt || !iw->wait)
+		return;
+
+	new = __add_dep(ie->ecxt, iw->wait);
+
+	/*
+	 * Deadlock detected. Let check_dl_bfs() report it.
+	 */
+	if (new) {
+		check_dl_bfs(new);
+		stale_iecxt(ie);
+		stale_iwait(iw);
+	}
+
+	/*
+	 * If !new, it would be the case of lack of object resource.
+	 * Just let it go and get checked by other chances. Retrying is
+	 * meaningless in that case.
+	 */
+}
+
+static void set_check_iecxt(struct dept_class *c, int irq,
+			    struct dept_ecxt *e)
+{
+	struct dept_iecxt *ie = iecxt(c, irq);
+
+	set_iecxt(ie, e);
+	__add_idep(ie, find_iw_bfs(c, irq));
+}
+
+static void set_check_iwait(struct dept_class *c, int irq,
+			    struct dept_wait *w)
+{
+	struct dept_iwait *iw = iwait(c, irq);
+
+	set_iwait(iw, w);
+	__add_idep(touch_iw_find_ie_bfs(c, irq), iw);
+}
+
+static void add_iecxt(struct dept_class *c, int irq, struct dept_ecxt *e,
+		      bool stack)
+{
+	/*
+	 * This access is safe since we ensure e->class has set locally.
+	 */
+	struct dept_task *dt = dept_task();
+	struct dept_iecxt *ie = iecxt(c, irq);
+
+	if (unlikely(READ_ONCE(ie->staled)))
+		return;
+
+	/*
+	 * Skip add_iecxt() if ie->ecxt has ever been set at least once.
+	 * Which means it has a valid ->ecxt or been staled.
+	 */
+	if (READ_ONCE(ie->ecxt))
+		return;
+
+	if (unlikely(!dept_lock()))
+		return;
+
+	if (unlikely(ie->staled))
+		goto unlock;
+	if (ie->ecxt)
+		goto unlock;
+
+	e->enirqf |= (1UL << irq);
+
+	/*
+	 * Should be NULL since it's the first time that these
+	 * enirq_{ip,stack}[irq] have ever set.
+	 */
+	DEPT_WARN_ON(e->enirq_ip[irq]);
+	DEPT_WARN_ON(e->enirq_stack[irq]);
+
+	e->enirq_ip[irq] = dt->enirq_ip[irq];
+	e->enirq_stack[irq] = stack ? get_current_stack() : NULL;
+
+	set_check_iecxt(c, irq, e);
+unlock:
+	dept_unlock();
+}
+
+static void add_iwait(struct dept_class *c, int irq, struct dept_wait *w)
+{
+	struct dept_iwait *iw = iwait(c, irq);
+
+	if (unlikely(READ_ONCE(iw->staled)))
+		return;
+
+	/*
+	 * Skip add_iwait() if iw->wait has ever been set at least once.
+	 * Which means it has a valid ->wait or been staled.
+	 */
+	if (READ_ONCE(iw->wait))
+		return;
+
+	if (unlikely(!dept_lock()))
+		return;
+
+	if (unlikely(iw->staled))
+		goto unlock;
+	if (iw->wait)
+		goto unlock;
+
+	w->irqf |= (1UL << irq);
+
+	/*
+	 * Should be NULL since it's the first time that these
+	 * irq_{ip,stack}[irq] have ever set.
+	 */
+	DEPT_WARN_ON(w->irq_ip[irq]);
+	DEPT_WARN_ON(w->irq_stack[irq]);
+
+	w->irq_ip[irq] = w->wait_ip;
+	w->irq_stack[irq] = get_current_stack();
+
+	set_check_iwait(c, irq, w);
+unlock:
+	dept_unlock();
+}
+
+static inline struct dept_wait_hist *hist(int pos)
+{
+	struct dept_task *dt = dept_task();
+
+	return dt->wait_hist + (pos % DEPT_MAX_WAIT_HIST);
+}
+
+static inline int hist_pos_next(void)
+{
+	struct dept_task *dt = dept_task();
+
+	return dt->wait_hist_pos % DEPT_MAX_WAIT_HIST;
+}
+
+static inline void hist_advance(void)
+{
+	struct dept_task *dt = dept_task();
+
+	dt->wait_hist_pos++;
+	dt->wait_hist_pos %= DEPT_MAX_WAIT_HIST;
+}
+
+static inline struct dept_wait_hist *new_hist(void)
+{
+	struct dept_wait_hist *wh = hist(hist_pos_next());
+
+	hist_advance();
+	return wh;
+}
+
+static void add_hist(struct dept_wait *w, unsigned int wg, unsigned int ctxt_id)
+{
+	struct dept_wait_hist *wh = new_hist();
+
+	if (likely(wh->wait))
+		put_wait(wh->wait);
+
+	wh->wait = get_wait(w);
+	wh->wgen = wg;
+	wh->ctxt_id = ctxt_id;
+}
+
+/*
+ * Should be called after setting up e's iecxt and w's iwait.
+ */
+static void add_dep(struct dept_ecxt *e, struct dept_wait *w)
+{
+	struct dept_class *fc = e->class;
+	struct dept_class *tc = w->class;
+	struct dept_dep *d;
+	int i;
+
+	if (lookup_dep(fc, tc))
+		return;
+
+	if (unlikely(!dept_lock()))
+		return;
+
+	/*
+	 * __add_dep() will lookup_dep() again with lock held.
+	 */
+	d = __add_dep(e, w);
+	if (d) {
+		check_dl_bfs(d);
+
+		for (i = 0; i < DEPT_IRQS_NR; i++) {
+			struct dept_iwait *fiw = iwait(fc, i);
+			struct dept_iecxt *found_ie;
+			struct dept_iwait *found_iw;
+
+			/*
+			 * '->touched == false' guarantees there's no
+			 * parent that has been set ->wait.
+			 */
+			if (!fiw->touched)
+				continue;
+
+			/*
+			 * find_iw_bfs() will untouch the iwait if
+			 * not found.
+			 */
+			found_iw = find_iw_bfs(fc, i);
+
+			if (!found_iw)
+				continue;
+
+			found_ie = touch_iw_find_ie_bfs(tc, i);
+			__add_idep(found_ie, found_iw);
+		}
+	}
+	dept_unlock();
+}
+
+static atomic_t wgen = ATOMIC_INIT(1);
+
+static void add_wait(struct dept_class *c, unsigned long ip,
+		     const char *w_fn, int ne)
+{
+	struct dept_task *dt = dept_task();
+	struct dept_wait *w;
+	unsigned int wg = 0U;
+	int irq;
+	int i;
+
+	w = new_wait();
+	if (unlikely(!w))
+		return;
+
+	WRITE_ONCE(w->class, get_class(c));
+	w->wait_ip = ip;
+	w->wait_fn = w_fn;
+	w->wait_stack = get_current_stack();
+
+	irq = cur_irq();
+	if (irq < DEPT_IRQS_NR)
+		add_iwait(c, irq, w);
+
+	/*
+	 * Avoid adding dependency between user aware nested ecxt and
+	 * wait.
+	 */
+	for (i = dt->ecxt_held_pos - 1; i >= 0; i--) {
+		struct dept_ecxt_held *eh;
+
+		eh = dt->ecxt_held + i;
+		if (eh->ecxt->class != c || eh->nest == ne)
+			add_dep(eh->ecxt, w);
+	}
+
+	if (!wait_consumed(w) && !rich_stack) {
+		if (w->wait_stack)
+			put_stack(w->wait_stack);
+		w->wait_stack = NULL;
+	}
+
+	/*
+	 * Avoid zero wgen.
+	 */
+	wg = atomic_inc_return(&wgen) ?: atomic_inc_return(&wgen);
+	add_hist(w, wg, cur_ctxt_id());
+
+	del_wait(w);
+}
+
+static bool add_ecxt(void *obj, struct dept_class *c, unsigned long ip,
+		     const char *c_fn, const char *e_fn, int ne)
+{
+	struct dept_task *dt = dept_task();
+	struct dept_ecxt_held *eh;
+	struct dept_ecxt *e;
+	unsigned long irqf;
+	int irq;
+
+	if (DEPT_WARN_ON(dt->ecxt_held_pos == DEPT_MAX_ECXT_HELD))
+		return false;
+
+	e = new_ecxt();
+	if (unlikely(!e))
+		return false;
+
+	e->class = get_class(c);
+	e->ecxt_ip = ip;
+	e->ecxt_stack = ip && rich_stack ? get_current_stack() : NULL;
+	e->event_fn = e_fn;
+	e->ecxt_fn = c_fn;
+
+	eh = dt->ecxt_held + (dt->ecxt_held_pos++);
+	eh->ecxt = get_ecxt(e);
+	eh->key = (unsigned long)obj;
+	eh->wgen = atomic_read(&wgen);
+	eh->nest = ne;
+
+	irqf = cur_enirqf();
+	for_each_set_bit(irq, &irqf, DEPT_IRQS_NR)
+		add_iecxt(c, irq, e, false);
+
+	del_ecxt(e);
+	return true;
+}
+
+static int find_ecxt_pos(unsigned long key, struct dept_class *c,
+			 bool newfirst)
+{
+	struct dept_task *dt = dept_task();
+	int i;
+
+	if (newfirst) {
+		for (i = dt->ecxt_held_pos - 1; i >= 0; i--) {
+			struct dept_ecxt_held *eh;
+
+			eh = dt->ecxt_held + i;
+			if (eh->key == key && eh->ecxt->class == c)
+				return i;
+		}
+	} else {
+		for (i = 0; i < dt->ecxt_held_pos; i++) {
+			struct dept_ecxt_held *eh;
+
+			eh = dt->ecxt_held + i;
+			if (eh->key == key && eh->ecxt->class == c)
+				return i;
+		}
+	}
+	return -1;
+}
+
+static bool pop_ecxt(void *obj, struct dept_class *c)
+{
+	struct dept_task *dt = dept_task();
+	unsigned long key = (unsigned long)obj;
+	int pos;
+	int i;
+
+	pos = find_ecxt_pos(key, c, true);
+	if (pos == -1)
+		return false;
+
+	put_ecxt(dt->ecxt_held[pos].ecxt);
+	dt->ecxt_held_pos--;
+
+	for (i = pos; i < dt->ecxt_held_pos; i++)
+		dt->ecxt_held[i] = dt->ecxt_held[i + 1];
+	return true;
+}
+
+static inline bool good_hist(struct dept_wait_hist *wh, unsigned int wg)
+{
+	return wh->wait != NULL && before(wg, wh->wgen);
+}
+
+/*
+ * Binary-search the ring buffer for the earliest valid wait.
+ */
+static int find_hist_pos(unsigned int wg)
+{
+	int oldest;
+	int l;
+	int r;
+	int pos;
+
+	oldest = hist_pos_next();
+	if (unlikely(good_hist(hist(oldest), wg))) {
+		DEPT_INFO_ONCE("Need to expand the ring buffer.\n");
+		return oldest;
+	}
+
+	l = oldest + 1;
+	r = oldest + DEPT_MAX_WAIT_HIST - 1;
+	for (pos = (l + r) / 2; l <= r; pos = (l + r) / 2) {
+		struct dept_wait_hist *p = hist(pos - 1);
+		struct dept_wait_hist *wh = hist(pos);
+
+		if (!good_hist(p, wg) && good_hist(wh, wg))
+			return pos % DEPT_MAX_WAIT_HIST;
+		if (good_hist(wh, wg))
+			r = pos - 1;
+		else
+			l = pos + 1;
+	}
+	return -1;
+}
+
+static void do_event(void *obj, struct dept_class *c, unsigned int wg,
+		     unsigned long ip)
+{
+	struct dept_task *dt = dept_task();
+	struct dept_wait_hist *wh;
+	struct dept_ecxt_held *eh;
+	unsigned long key = (unsigned long)obj;
+	unsigned int ctxt_id;
+	int end;
+	int pos;
+	int i;
+
+	/*
+	 * The event was triggered before wait.
+	 */
+	if (!wg)
+		return;
+
+	pos = find_ecxt_pos(key, c, false);
+	if (pos == -1)
+		return;
+
+	eh = dt->ecxt_held + pos;
+	eh->ecxt->event_ip = ip;
+	eh->ecxt->event_stack = get_current_stack();
+
+	/*
+	 * The ecxt already has done what it needs.
+	 */
+	if (!before(wg, eh->wgen))
+		return;
+
+	pos = find_hist_pos(wg);
+	if (pos == -1)
+		return;
+
+	ctxt_id = cur_ctxt_id();
+	end = hist_pos_next();
+	end = end > pos ? end : end + DEPT_MAX_WAIT_HIST;
+	for (wh = hist(pos); pos < end; wh = hist(++pos)) {
+		if (wh->ctxt_id == ctxt_id)
+			add_dep(eh->ecxt, wh->wait);
+		if (!before(wh->wgen, eh->wgen))
+			break;
+	}
+
+	for (i = 0; i < DEPT_IRQS_NR; i++) {
+		struct dept_ecxt *e;
+
+		if (before(dt->wgen_enirq[i], wg))
+			continue;
+
+		e = eh->ecxt;
+		add_iecxt(e->class, i, e, false);
+	}
+}
+
+static void del_dep_rcu(struct rcu_head *rh)
+{
+	struct dept_dep *d = container_of(rh, struct dept_dep, rh);
+
+	preempt_disable();
+	del_dep(d);
+	preempt_enable();
+}
+
+/*
+ * NOTE: Must be called with dept_lock held.
+ */
+static void disconnect_class(struct dept_class *c)
+{
+	struct dept_dep *d, *n;
+	int i;
+
+	list_for_each_entry_safe(d, n, &c->dep_head, dep_node) {
+		list_del_rcu(&d->dep_node);
+		list_del_rcu(&d->dep_rev_node);
+		hash_del_dep(d);
+		call_rcu(&d->rh, del_dep_rcu);
+	}
+
+	list_for_each_entry_safe(d, n, &c->dep_rev_head, dep_rev_node) {
+		list_del_rcu(&d->dep_node);
+		list_del_rcu(&d->dep_rev_node);
+		hash_del_dep(d);
+		call_rcu(&d->rh, del_dep_rcu);
+	}
+
+	for (i = 0; i < DEPT_IRQS_NR; i++) {
+		stale_iecxt(iecxt(c, i));
+		stale_iwait(iwait(c, i));
+	}
+}
+
+/*
+ * IRQ context control
+ * =====================================================================
+ * Whether a wait is in {hard,soft}-IRQ context or whether
+ * {hard,soft}-IRQ has been enabled on the way to an event is very
+ * important to check dependency. All those things should be tracked.
+ */
+
+static inline unsigned long cur_enirqf(void)
+{
+	struct dept_task *dt = dept_task();
+	int he = dt->hardirqs_enabled;
+	int se = dt->softirqs_enabled;
+
+	if (he)
+		return DEPT_HIRQF | (se ? DEPT_SIRQF : 0UL);
+	return 0UL;
+}
+
+static inline int cur_irq(void)
+{
+	if (lockdep_softirq_context(current))
+		return DEPT_SIRQ;
+	if (lockdep_hardirq_context())
+		return DEPT_HIRQ;
+	return DEPT_IRQS_NR;
+}
+
+static inline unsigned int cur_ctxt_id(void)
+{
+	struct dept_task *dt = dept_task();
+	int irq = cur_irq();
+
+	/*
+	 * Normal process context
+	 */
+	if (irq == DEPT_IRQS_NR)
+		return 0U;
+
+	return dt->irq_id[irq] | (1UL << irq);
+}
+
+static void enirq_transition(int irq)
+{
+	struct dept_task *dt = dept_task();
+	int i;
+
+	/*
+	 * READ wgen >= wgen of an event with IRQ enabled has been
+	 * observed on the way to the event means, the IRQ can cut in
+	 * within the ecxt. Used for cross-event detection.
+	 *
+	 *    wait context	event context(ecxt)
+	 *    ------------	-------------------
+	 *    wait event
+	 *       WRITE wgen
+	 *			observe IRQ enabled
+	 *			   READ wgen
+	 *			   keep the wgen locally
+	 *
+	 *			on the event
+	 *			   check the local wgen
+	 */
+	dt->wgen_enirq[irq] = atomic_read(&wgen);
+
+	for (i = dt->ecxt_held_pos - 1; i >= 0; i--) {
+		struct dept_ecxt_held *eh;
+		struct dept_ecxt *e;
+
+		eh = dt->ecxt_held + i;
+		e = eh->ecxt;
+		add_iecxt(e->class, irq, e, true);
+	}
+}
+
+static void enirq_update(unsigned long ip)
+{
+	struct dept_task *dt = dept_task();
+	unsigned long irqf;
+	unsigned long prev;
+	int irq;
+
+	prev = dt->eff_enirqf;
+	irqf = cur_enirqf();
+	dt->eff_enirqf = irqf;
+
+	/*
+	 * Do enirq_transition() only on an OFF -> ON transition.
+	 */
+	for_each_set_bit(irq, &irqf, DEPT_IRQS_NR) {
+		if (prev & (1UL << irq))
+			continue;
+
+		dt->enirq_ip[irq] = ip;
+		enirq_transition(irq);
+	}
+}
+
+void dept_aware_softirqs_enable(void)
+{
+	dept_task()->softirqs_enabled = true;
+}
+
+void dept_aware_softirqs_disable(void)
+{
+	dept_task()->softirqs_enabled = false;
+}
+
+void dept_aware_hardirqs_enable(void)
+{
+	dept_task()->hardirqs_enabled = true;
+}
+EXPORT_SYMBOL_GPL(dept_aware_hardirqs_enable);
+
+void dept_aware_hardirqs_disable(void)
+{
+	dept_task()->hardirqs_enabled = false;
+}
+EXPORT_SYMBOL_GPL(dept_aware_hardirqs_disable);
+
+/*
+ * Ensure it has been called on ON/OFF transition.
+ */
+void dept_enirq_transition(unsigned long ip)
+{
+	struct dept_task *dt = dept_task();
+	unsigned long flags;
+
+	if (unlikely(READ_ONCE(dept_stop) || in_nmi()))
+		return;
+
+	/*
+	 * IRQ ON/OFF transition might happen while Dept is working.
+	 * We cannot handle recursive entrance. Just ingnore it.
+	 * Only transitions outside of Dept will be considered.
+	 */
+	if (dt->recursive)
+		return;
+
+	flags = dept_enter();
+
+	enirq_update(ip);
+
+	dept_exit(flags);
+}
+
+/*
+ * Ensure it's the outmost softirq context.
+ */
+void dept_softirq_enter(void)
+{
+	struct dept_task *dt = dept_task();
+
+	dt->irq_id[DEPT_SIRQ] += (1UL << DEPT_IRQS_NR);
+}
+
+/*
+ * Ensure it's the outmost hardirq context.
+ */
+void dept_hardirq_enter(void)
+{
+	struct dept_task *dt = dept_task();
+
+	dt->irq_id[DEPT_HIRQ] += (1UL << DEPT_IRQS_NR);
+}
+
+/*
+ * DEPT API
+ * =====================================================================
+ * Main DEPT APIs.
+ */
+
+static inline void clean_classes_cache(struct dept_key *k)
+{
+	int i;
+
+	for (i = 0; i < DEPT_MAX_SUBCLASSES_CACHE; i++)
+		k->classes[i] = NULL;
+}
+
+void dept_map_init(struct dept_map *m, struct dept_key *k, int sub,
+		   const char *n)
+{
+	unsigned long flags;
+
+	if (unlikely(READ_ONCE(dept_stop) || in_nmi()))
+		return;
+
+	if (sub < 0 || sub >= DEPT_MAX_SUBCLASSES_USR) {
+		m->nocheck = true;
+		return;
+	}
+
+	/*
+	 * Allow recursive entrance.
+	 */
+	flags = dept_enter_recursive();
+
+	clean_classes_cache(&m->keys_local);
+
+	m->sub_usr = sub;
+	m->keys = k;
+	m->name = n;
+	m->wgen = 0U;
+	m->nocheck = false;
+
+	dept_exit_recursive(flags);
+}
+EXPORT_SYMBOL_GPL(dept_map_init);
+
+void dept_map_reinit(struct dept_map *m)
+{
+	unsigned long flags;
+
+	if (unlikely(READ_ONCE(dept_stop) || in_nmi()))
+		return;
+
+	if (m->nocheck)
+		return;
+
+	/*
+	 * Allow recursive entrance.
+	 */
+	flags = dept_enter_recursive();
+
+	clean_classes_cache(&m->keys_local);
+	m->wgen = 0U;
+
+	dept_exit_recursive(flags);
+}
+EXPORT_SYMBOL_GPL(dept_map_reinit);
+
+void dept_map_nocheck(struct dept_map *m)
+{
+	unsigned long flags;
+
+	if (unlikely(READ_ONCE(dept_stop) || in_nmi()))
+		return;
+
+	/*
+	 * Allow recursive entrance.
+	 */
+	flags = dept_enter_recursive();
+
+	m->nocheck = true;
+
+	dept_exit_recursive(flags);
+}
+EXPORT_SYMBOL_GPL(dept_map_nocheck);
+
+static LIST_HEAD(classes);
+
+static inline bool within(const void *addr, void *start, unsigned long size)
+{
+	return addr >= start && addr < start + size;
+}
+
+void dept_free_range(void *start, unsigned int sz)
+{
+	struct dept_task *dt = dept_task();
+	struct dept_class *c, *n;
+	unsigned long flags;
+
+	if (unlikely(READ_ONCE(dept_stop) || in_nmi()))
+		return;
+
+	if (dt->recursive) {
+		DEPT_STOP("Should successfully free the objects.\n");
+		return;
+	}
+
+	flags = dept_enter();
+
+	/*
+	 * dept_free_range() should not fail.
+	 *
+	 * FIXME: Should be fixed if dept_free_range() causes deadlock
+	 * with dept_lock().
+	 */
+	while (unlikely(!dept_lock()))
+		cpu_relax();
+
+	list_for_each_entry_safe(c, n, &classes, all_node) {
+		if (!within((void *)c->key, start, sz) &&
+		    !within(c->name, start, sz))
+			continue;
+
+		hash_del_class(c);
+		disconnect_class(c);
+		list_del(&c->all_node);
+		inval_class(c);
+
+		/*
+		 * Actual deletion will happen on the rcu callback
+		 * that has been added in disconnect_class().
+		 */
+		del_class(c);
+	}
+	dept_unlock();
+	dept_exit(flags);
+
+	/*
+	 * Wait until even lockless hash_lookup_class() for the class
+	 * returns NULL.
+	 */
+	might_sleep();
+	synchronize_rcu();
+}
+
+static inline int map_sub(struct dept_map *m, int e)
+{
+	return m->sub_usr + e * DEPT_MAX_SUBCLASSES_USR;
+}
+
+static struct dept_class *check_new_class(struct dept_key *local,
+					  struct dept_key *k, int sub,
+					  const char *n)
+{
+	struct dept_class *c = NULL;
+
+	if (DEPT_WARN_ON(sub >= DEPT_MAX_SUBCLASSES))
+		return NULL;
+
+	if (DEPT_WARN_ON(!k))
+		return NULL;
+
+	if (sub < DEPT_MAX_SUBCLASSES_CACHE)
+		c = READ_ONCE(local->classes[sub]);
+
+	if (c)
+		return c;
+
+	c = lookup_class((unsigned long)k->subkeys + sub);
+	if (c)
+		goto caching;
+
+	if (unlikely(!dept_lock()))
+		return NULL;
+
+	c = lookup_class((unsigned long)k->subkeys + sub);
+	if (unlikely(c))
+		goto unlock;
+
+	c = new_class();
+	if (unlikely(!c))
+		goto unlock;
+
+	c->name = n;
+	c->sub = sub;
+	c->key = (unsigned long)(k->subkeys + sub);
+	hash_add_class(c);
+	list_add(&c->all_node, &classes);
+unlock:
+	dept_unlock();
+caching:
+	/*
+	 * Should be cached even if c == NULL, to reflect the case that
+	 * the class has been deleted.
+	 */
+	if (sub < DEPT_MAX_SUBCLASSES_CACHE)
+		WRITE_ONCE(local->classes[sub], c);
+
+	return c;
+}
+
+static void __dept_wait(struct dept_map *m, unsigned long w_f,
+			unsigned long ip, const char *w_fn, int ne)
+{
+	int e;
+
+	/*
+	 * Be as conservative as possible. In case of mulitple waits for
+	 * a single dept_map, we are going to keep only the last wait's
+	 * wgen for simplicity - keeping all wgens seems overengineering.
+	 *
+	 * Of course, it might cause missing some dependencies that
+	 * would rarely, probabily never, happen but it helps avoid
+	 * false positive report.
+	 */
+	for_each_set_bit(e, &w_f, DEPT_MAX_SUBCLASSES_EVT) {
+		struct dept_class *c;
+		struct dept_key *k;
+
+		k = m->keys ?: &m->keys_local;
+		c = check_new_class(&m->keys_local, k,
+				    map_sub(m, e), m->name);
+		if (!c)
+			continue;
+
+		add_wait(c, ip, w_fn, ne);
+	}
+}
+
+void dept_wait(struct dept_map *m, unsigned long w_f, unsigned long ip,
+	       const char *w_fn, int ne)
+{
+	struct dept_task *dt = dept_task();
+	unsigned long flags;
+
+	if (unlikely(READ_ONCE(dept_stop) || in_nmi()))
+		return;
+
+	if (dt->recursive)
+		return;
+
+	if (m->nocheck)
+		return;
+
+	flags = dept_enter();
+
+	__dept_wait(m, w_f, ip, w_fn, ne);
+
+	dept_exit(flags);
+}
+EXPORT_SYMBOL_GPL(dept_wait);
+
+static inline void stage_map(struct dept_task *dt, struct dept_map *m)
+{
+	dt->stage_m = m;
+}
+
+static inline void unstage_map(struct dept_task *dt)
+{
+	dt->stage_m = NULL;
+}
+
+static inline struct dept_map *staged_map(struct dept_task *dt)
+{
+	return dt->stage_m;
+}
+
+void dept_stage_wait(struct dept_map *m, unsigned long w_f,
+		     const char *w_fn, int ne)
+{
+	struct dept_task *dt = dept_task();
+	unsigned long flags;
+
+	if (unlikely(READ_ONCE(dept_stop) || in_nmi()))
+		return;
+
+	if (m->nocheck)
+		return;
+
+	/*
+	 * Allow recursive entrance.
+	 */
+	flags = dept_enter_recursive();
+
+	stage_map(dt, m);
+
+	dt->stage_w_f = w_f;
+	dt->stage_w_fn = w_fn;
+	dt->stage_ne = ne;
+
+	/*
+	 * Disable the map just in case real sleep won't happen. This
+	 * will be enabled at dept_ask_event_wait_commit().
+	 */
+	WRITE_ONCE(m->wgen, 0U);
+
+	dept_exit_recursive(flags);
+}
+EXPORT_SYMBOL_GPL(dept_stage_wait);
+
+void dept_clean_stage(void)
+{
+	struct dept_task *dt = dept_task();
+	unsigned long flags;
+
+	if (unlikely(READ_ONCE(dept_stop) || in_nmi()))
+		return;
+
+	/*
+	 * Allow recursive entrance.
+	 */
+	flags = dept_enter_recursive();
+
+	unstage_map(dt);
+
+	dt->stage_w_f = 0UL;
+	dt->stage_w_fn = NULL;
+	dt->stage_ne = 0;
+
+	dept_exit_recursive(flags);
+}
+EXPORT_SYMBOL_GPL(dept_clean_stage);
+
+/*
+ * Always called from __schedule().
+ */
+void dept_ask_event_wait_commit(unsigned long ip)
+{
+	struct dept_task *dt = dept_task();
+	unsigned long flags;
+	unsigned int wg;
+	struct dept_map *m;
+	unsigned long w_f;
+	const char *w_fn;
+	int ne;
+
+	if (unlikely(READ_ONCE(dept_stop) || in_nmi()))
+		return;
+
+	if (dt->recursive) {
+		flags = dept_enter_recursive();
+
+		/*
+		 * Dept won't work with this map even though anyway an
+		 * event context has been just asked. Don't make it
+		 * confused at that time handling the event. Disable it
+		 * until the next real case.
+		 */
+		m = staged_map(dt);
+		if (m)
+			WRITE_ONCE(m->wgen, 0U);
+
+		dept_exit_recursive(flags);
+		return;
+	}
+
+	flags = dept_enter();
+
+	m = staged_map(dt);
+
+	/*
+	 * Checks if current has staged a wait before __schedule().
+	 */
+	if (!m)
+		goto exit;
+
+	if (m->nocheck)
+		goto exit;
+
+	w_f = dt->stage_w_f;
+	w_fn = dt->stage_w_fn;
+	ne = dt->stage_ne;
+
+	/*
+	 * Avoid zero wgen.
+	 */
+	wg = atomic_inc_return(&wgen) ?: atomic_inc_return(&wgen);
+	WRITE_ONCE(m->wgen, wg);
+
+	__dept_wait(m, w_f, ip, w_fn, ne);
+exit:
+	dept_exit(flags);
+}
+
+void dept_ecxt_enter(struct dept_map *m, unsigned long e_f, unsigned long ip,
+		     const char *c_fn, const char *e_fn, int ne)
+{
+	struct dept_task *dt = dept_task();
+	unsigned long flags;
+	struct dept_class *c;
+	struct dept_key *k;
+	int e;
+
+	if (unlikely(READ_ONCE(dept_stop) || in_nmi()))
+		return;
+
+	if (dt->recursive) {
+		dt->missing_ecxt++;
+		return;
+	}
+
+	if (m->nocheck)
+		return;
+
+	flags = dept_enter();
+
+        e = find_first_bit(&e_f, DEPT_MAX_SUBCLASSES_EVT);
+
+	if (e >= DEPT_MAX_SUBCLASSES_EVT)
+		goto missing_ecxt;
+
+	/*
+	 * The caller passed more than single event? Warn it so that the
+	 * caller code can be fixed, and handle the event corresponding
+	 * to the first bit anyway.
+	 */
+	DEPT_WARN_ON(1UL << e != e_f);
+
+	k = m->keys ?: &m->keys_local;
+	c = check_new_class(&m->keys_local, k, map_sub(m, e), m->name);
+
+	if (c && add_ecxt((void *)m, c, ip, c_fn, e_fn, ne))
+		goto exit;
+missing_ecxt:
+	dt->missing_ecxt++;
+exit:
+	dept_exit(flags);
+}
+EXPORT_SYMBOL_GPL(dept_ecxt_enter);
+
+void dept_ask_event(struct dept_map *m)
+{
+	unsigned long flags;
+	unsigned int wg;
+
+	if (unlikely(READ_ONCE(dept_stop) || in_nmi()))
+		return;
+
+	if (m->nocheck)
+		return;
+
+	/*
+	 * Allow recursive entrance.
+	 */
+	flags = dept_enter_recursive();
+
+	/*
+	 * Avoid zero wgen.
+	 */
+	wg = atomic_inc_return(&wgen) ?: atomic_inc_return(&wgen);
+	WRITE_ONCE(m->wgen, wg);
+
+	dept_exit_recursive(flags);
+}
+EXPORT_SYMBOL_GPL(dept_ask_event);
+
+void dept_event(struct dept_map *m, unsigned long e_f, unsigned long ip,
+		const char *e_fn)
+{
+	struct dept_task *dt = dept_task();
+	unsigned long flags;
+	struct dept_class *c;
+	struct dept_key *k;
+	int e;
+
+	if (unlikely(READ_ONCE(dept_stop) || in_nmi()))
+		return;
+
+	if (dt->recursive) {
+		/*
+		 * Dept won't work with this map even though anyway an
+		 * event has been just triggered. Don't make it confused
+		 * at that time handling the next event. Disable it
+		 * until the next real case.
+		 */
+		WRITE_ONCE(m->wgen, 0U);
+		return;
+	}
+
+	if (m->nocheck)
+		return;
+
+	flags = dept_enter();
+
+        e = find_first_bit(&e_f, DEPT_MAX_SUBCLASSES_EVT);
+
+	if (DEPT_WARN_ON(e >= DEPT_MAX_SUBCLASSES_EVT))
+		goto exit;
+
+	/*
+	 * The caller passed more than single event? Warn it so that the
+	 * caller can be fixed, and handle the event corresponding to
+	 * the first bit anyway.
+	 */
+	DEPT_WARN_ON(1UL << e != e_f);
+
+	k = m->keys ?: &m->keys_local;
+	c = check_new_class(&m->keys_local, k, map_sub(m, e), m->name);
+
+	if (c && add_ecxt((void *)m, c, 0UL, NULL, e_fn, 0)) {
+		do_event((void *)m, c, READ_ONCE(m->wgen), ip);
+		pop_ecxt((void *)m, c);
+	}
+exit:
+	/*
+	 * Keep the map diabled until the next sleep.
+	 */
+	WRITE_ONCE(m->wgen, 0U);
+
+	dept_exit(flags);
+}
+EXPORT_SYMBOL_GPL(dept_event);
+
+void dept_ecxt_exit(struct dept_map *m, unsigned long e_f,
+		    unsigned long ip)
+{
+	struct dept_task *dt = dept_task();
+	unsigned long flags;
+	struct dept_class *c;
+	struct dept_key *k;
+	int e;
+
+	if (unlikely(READ_ONCE(dept_stop) || in_nmi()))
+		return;
+
+	if (dt->recursive) {
+		dt->missing_ecxt--;
+		return;
+	}
+
+	if (m->nocheck)
+		return;
+
+	flags = dept_enter();
+
+	e = find_first_bit(&e_f, DEPT_MAX_SUBCLASSES_EVT);
+
+	if (e >= DEPT_MAX_SUBCLASSES_EVT)
+		goto missing_ecxt;
+
+	/*
+	 * The caller passed more than single event? Warn it so that the
+	 * caller can be fixed, and handle the event corresponding to
+	 * the first bit anyway.
+	 */
+	DEPT_WARN_ON(1UL << e != e_f);
+
+	k = m->keys ?: &m->keys_local;
+	c = check_new_class(&m->keys_local, k, map_sub(m, e), m->name);
+
+	if (c && pop_ecxt((void *)m, c))
+		goto exit;
+missing_ecxt:
+	dt->missing_ecxt--;
+exit:
+	dept_exit(flags);
+}
+EXPORT_SYMBOL_GPL(dept_ecxt_exit);
+
+void dept_task_exit(struct task_struct *t)
+{
+	struct dept_task *dt = &t->dept_task;
+	int i;
+
+	raw_local_irq_disable();
+
+	if (dt->stack)
+		put_stack(dt->stack);
+
+	for (i = 0; i < dt->ecxt_held_pos; i++)
+		put_ecxt(dt->ecxt_held[i].ecxt);
+
+	for (i = 0; i < DEPT_MAX_WAIT_HIST; i++)
+		if (dt->wait_hist[i].wait)
+			put_wait(dt->wait_hist[i].wait);
+
+	dept_off();
+
+	raw_local_irq_enable();
+}
+
+void dept_task_init(struct task_struct *t)
+{
+	memset(&t->dept_task, 0x0, sizeof(struct dept_task));
+}
+
+void dept_key_init(struct dept_key *k)
+{
+	struct dept_task *dt = dept_task();
+	unsigned long flags;
+	int sub;
+
+	if (unlikely(READ_ONCE(dept_stop) || in_nmi()))
+		return;
+
+	if (dt->recursive) {
+		DEPT_STOP("Key initialization fails.\n");
+		return;
+	}
+
+	flags = dept_enter();
+
+	/*
+	 * dept_key_init() should not fail.
+	 *
+	 * FIXME: Should be fixed if dept_key_init() causes deadlock
+	 * with dept_lock().
+	 */
+	while (unlikely(!dept_lock()))
+		cpu_relax();
+
+	for (sub = 0; sub < DEPT_MAX_SUBCLASSES; sub++) {
+		struct dept_class *c;
+
+		c = lookup_class((unsigned long)k->subkeys + sub);
+		if (!c)
+			continue;
+
+		DEPT_STOP("The class(%s/%d) has not been removed.\n",
+			  c->name, sub);
+		break;
+	}
+
+	dept_unlock();
+	dept_exit(flags);
+}
+EXPORT_SYMBOL_GPL(dept_key_init);
+
+void dept_key_destroy(struct dept_key *k)
+{
+	struct dept_task *dt = dept_task();
+	unsigned long flags;
+	int sub;
+
+	if (unlikely(READ_ONCE(dept_stop) || in_nmi()))
+		return;
+
+	if (dt->recursive) {
+		DEPT_STOP("Key destroying fails.\n");
+		return;
+	}
+
+	flags = dept_enter();
+
+	/*
+	 * dept_key_destroy() should not fail.
+	 *
+	 * FIXME: Should be fixed if dept_key_destroy() causes deadlock
+	 * with dept_lock().
+	 */
+	while (unlikely(!dept_lock()))
+		cpu_relax();
+
+	for (sub = 0; sub < DEPT_MAX_SUBCLASSES; sub++) {
+		struct dept_class *c;
+
+		c = lookup_class((unsigned long)k->subkeys + sub);
+		if (!c)
+			continue;
+
+		hash_del_class(c);
+		disconnect_class(c);
+		list_del(&c->all_node);
+		inval_class(c);
+
+		/*
+		 * Actual deletion will happen on the rcu callback
+		 * that has been added in disconnect_class().
+		 */
+		del_class(c);
+	}
+
+	dept_unlock();
+	dept_exit(flags);
+
+	/*
+	 * Wait until even lockless hash_lookup_class() for the class
+	 * returns NULL.
+	 */
+	might_sleep();
+	synchronize_rcu();
+}
+EXPORT_SYMBOL_GPL(dept_key_destroy);
+
+static void move_llist(struct llist_head *to, struct llist_head *from)
+{
+	struct llist_node *first = llist_del_all(from);
+	struct llist_node *last;
+
+	if (!first)
+		return;
+
+	for (last = first; last->next; last = last->next);
+	llist_add_batch(first, last, to);
+}
+
+static void migrate_per_cpu_pool(void)
+{
+	const int boot_cpu = 0;
+	int i;
+
+	/*
+	 * The boot CPU has been using the temperal local pool so far.
+	 * From now on that per_cpu areas have been ready, use the
+	 * per_cpu local pool instead.
+	 */
+	DEPT_WARN_ON(smp_processor_id() != boot_cpu);
+	for (i = 0; i < OBJECT_NR; i++) {
+		struct llist_head *from;
+		struct llist_head *to;
+
+		from = &pool[i].boot_pool;
+		to = per_cpu_ptr(pool[i].lpool, boot_cpu);
+		move_llist(to, from);
+	}
+}
+
+#define B2KB(B) ((B) / 1024)
+
+/*
+ * Should be called after setup_per_cpu_areas() and before no non-boot
+ * CPUs have been on.
+ */
+void __init dept_init(void)
+{
+	size_t mem_total = 0;
+
+	local_irq_disable();
+	dept_per_cpu_ready = 1;
+	migrate_per_cpu_pool();
+	local_irq_enable();
+
+#define OBJECT(id, nr) mem_total += sizeof(struct dept_##id) * nr;
+	#include "dept_object.h"
+#undef  OBJECT
+#define HASH(id, bits) mem_total += sizeof(struct hlist_head) * (1UL << bits);
+	#include "dept_hash.h"
+#undef  HASH
+
+	pr_info("DEPendency Tracker: Copyright (c) 2020 LG Electronics, Inc., Byungchul Park\n");
+	pr_info("... DEPT_MAX_STACK_ENTRY: %d\n", DEPT_MAX_STACK_ENTRY);
+	pr_info("... DEPT_MAX_WAIT_HIST  : %d\n", DEPT_MAX_WAIT_HIST);
+	pr_info("... DEPT_MAX_ECXT_HELD  : %d\n", DEPT_MAX_ECXT_HELD);
+	pr_info("... DEPT_MAX_SUBCLASSES : %d\n", DEPT_MAX_SUBCLASSES);
+#define OBJECT(id, nr)							\
+	pr_info("... memory used by %s: %zu KB\n",			\
+	       #id, B2KB(sizeof(struct dept_##id) * nr));
+	#include "dept_object.h"
+#undef  OBJECT
+#define HASH(id, bits)							\
+	pr_info("... hash list head used by %s: %zu KB\n",		\
+	       #id, B2KB(sizeof(struct hlist_head) * (1UL << bits)));
+	#include "dept_hash.h"
+#undef  HASH
+	pr_info("... total memory used by objects and hashs: %zu KB\n", B2KB(mem_total));
+	pr_info("... per task memory footprint: %zu bytes\n", sizeof(struct dept_task));
+}
diff --git a/kernel/dependency/dept_hash.h b/kernel/dependency/dept_hash.h
new file mode 100644
index 00000000..fd85aab
--- /dev/null
+++ b/kernel/dependency/dept_hash.h
@@ -0,0 +1,10 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * HASH(id, bits)
+ *
+ * id  : Id for the object of struct dept_##id.
+ * bits: 1UL << bits is the hash table size.
+ */
+
+HASH(dep, 12)
+HASH(class, 12)
diff --git a/kernel/dependency/dept_object.h b/kernel/dependency/dept_object.h
new file mode 100644
index 00000000..0b7eb16
--- /dev/null
+++ b/kernel/dependency/dept_object.h
@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * OBJECT(id, nr)
+ *
+ * id: Id for the object of struct dept_##id.
+ * nr: # of the object that should be kept in the pool.
+ */
+
+OBJECT(dep, 1024 * 8)
+OBJECT(class, 1024 * 8)
+OBJECT(stack, 1024 * 32)
+OBJECT(ecxt, 1024 * 16)
+OBJECT(wait, 1024 * 32)
diff --git a/kernel/exit.c b/kernel/exit.c
index f072959..bac41ee 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -844,6 +844,7 @@ void __noreturn do_exit(long code)
 	exit_tasks_rcu_finish();
 
 	lockdep_free_task(tsk);
+	dept_task_exit(tsk);
 	do_task_dead();
 }
 
diff --git a/kernel/fork.c b/kernel/fork.c
index 9796897..68f7154 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -98,6 +98,7 @@
 #include <linux/io_uring.h>
 #include <linux/bpf.h>
 #include <linux/sched/mm.h>
+#include <linux/dept.h>
 
 #include <asm/pgalloc.h>
 #include <linux/uaccess.h>
@@ -2187,6 +2188,7 @@ static __latent_entropy struct task_struct *copy_process(
 #ifdef CONFIG_LOCKDEP
 	lockdep_init_task(p);
 #endif
+	dept_task_init(p);
 
 #ifdef CONFIG_DEBUG_MUTEXES
 	p->blocked_on = NULL; /* not blocked yet */
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index c06cab6..2175f9c 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1182,7 +1182,7 @@ static inline struct hlist_head *keyhashentry(const struct lock_class_key *key)
 }
 
 /* Register a dynamically allocated key. */
-void lockdep_register_key(struct lock_class_key *key)
+void __lockdep_register_key(struct lock_class_key *key)
 {
 	struct hlist_head *hash_head;
 	struct lock_class_key *k;
@@ -1205,7 +1205,7 @@ void lockdep_register_key(struct lock_class_key *key)
 restore_irqs:
 	raw_local_irq_restore(flags);
 }
-EXPORT_SYMBOL_GPL(lockdep_register_key);
+EXPORT_SYMBOL_GPL(__lockdep_register_key);
 
 /* Check whether a key has been registered as a dynamic key. */
 static bool is_dynamic_key(const struct lock_class_key *key)
@@ -4243,7 +4243,7 @@ static void __trace_hardirqs_on_caller(void)
  * stops watching. After the RCU transition lockdep_hardirqs_on() has to be
  * invoked to set the final state.
  */
-void lockdep_hardirqs_on_prepare(unsigned long ip)
+void __lockdep_hardirqs_on_prepare(unsigned long ip)
 {
 	if (unlikely(!debug_locks))
 		return;
@@ -4294,9 +4294,9 @@ void lockdep_hardirqs_on_prepare(unsigned long ip)
 	__trace_hardirqs_on_caller();
 	lockdep_recursion_finish();
 }
-EXPORT_SYMBOL_GPL(lockdep_hardirqs_on_prepare);
+EXPORT_SYMBOL_GPL(__lockdep_hardirqs_on_prepare);
 
-void noinstr lockdep_hardirqs_on(unsigned long ip)
+void noinstr __lockdep_hardirqs_on(unsigned long ip)
 {
 	struct irqtrace_events *trace = &current->irqtrace;
 
@@ -4358,12 +4358,12 @@ void noinstr lockdep_hardirqs_on(unsigned long ip)
 	trace->hardirq_enable_event = ++trace->irq_events;
 	debug_atomic_inc(hardirqs_on_events);
 }
-EXPORT_SYMBOL_GPL(lockdep_hardirqs_on);
+EXPORT_SYMBOL_GPL(__lockdep_hardirqs_on);
 
 /*
  * Hardirqs were disabled:
  */
-void noinstr lockdep_hardirqs_off(unsigned long ip)
+void noinstr __lockdep_hardirqs_off(unsigned long ip)
 {
 	if (unlikely(!debug_locks))
 		return;
@@ -4400,12 +4400,12 @@ void noinstr lockdep_hardirqs_off(unsigned long ip)
 		debug_atomic_inc(redundant_hardirqs_off);
 	}
 }
-EXPORT_SYMBOL_GPL(lockdep_hardirqs_off);
+EXPORT_SYMBOL_GPL(__lockdep_hardirqs_off);
 
 /*
  * Softirqs will be enabled:
  */
-void lockdep_softirqs_on(unsigned long ip)
+void __lockdep_softirqs_on(unsigned long ip)
 {
 	struct irqtrace_events *trace = &current->irqtrace;
 
@@ -4445,7 +4445,7 @@ void lockdep_softirqs_on(unsigned long ip)
 /*
  * Softirqs were disabled:
  */
-void lockdep_softirqs_off(unsigned long ip)
+void __lockdep_softirqs_off(unsigned long ip)
 {
 	if (unlikely(!lockdep_enabled()))
 		return;
@@ -4773,7 +4773,7 @@ static inline int check_wait_context(struct task_struct *curr,
 /*
  * Initialize a lock instance's lock-class mapping info:
  */
-void lockdep_init_map_type(struct lockdep_map *lock, const char *name,
+void __lockdep_init_map_type(struct lockdep_map *lock, const char *name,
 			    struct lock_class_key *key, int subclass,
 			    u8 inner, u8 outer, u8 lock_type)
 {
@@ -4833,7 +4833,7 @@ void lockdep_init_map_type(struct lockdep_map *lock, const char *name,
 		raw_local_irq_restore(flags);
 	}
 }
-EXPORT_SYMBOL_GPL(lockdep_init_map_type);
+EXPORT_SYMBOL_GPL(__lockdep_init_map_type);
 
 struct lock_class_key __lockdep_no_validate__;
 EXPORT_SYMBOL_GPL(__lockdep_no_validate__);
@@ -6298,7 +6298,7 @@ void lockdep_reset_lock(struct lockdep_map *lock)
  * key irrespective of debug_locks to avoid potential invalid access to freed
  * memory in lock_class entry.
  */
-void lockdep_unregister_key(struct lock_class_key *key)
+void __lockdep_unregister_key(struct lock_class_key *key)
 {
 	struct hlist_head *hash_head = keyhashentry(key);
 	struct lock_class_key *k;
@@ -6333,7 +6333,7 @@ void lockdep_unregister_key(struct lock_class_key *key)
 	/* Wait until is_dynamic_key() has finished accessing k->hash_entry. */
 	synchronize_rcu();
 }
-EXPORT_SYMBOL_GPL(lockdep_unregister_key);
+EXPORT_SYMBOL_GPL(__lockdep_unregister_key);
 
 void __init lockdep_init(void)
 {
diff --git a/kernel/module.c b/kernel/module.c
index 6cea788..0953f99 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2205,6 +2205,7 @@ static void free_module(struct module *mod)
 
 	/* Free lock-classes; relies on the preceding sync_rcu(). */
 	lockdep_free_key_range(mod->core_layout.base, mod->core_layout.size);
+	dept_free_range(mod->core_layout.base, mod->core_layout.size);
 
 	/* Finally, free the core (containing the module structure) */
 	module_memfree(mod->core_layout.base);
@@ -4159,6 +4160,7 @@ static int load_module(struct load_info *info, const char __user *uargs,
  free_module:
 	/* Free lock-classes; relies on the preceding sync_rcu() */
 	lockdep_free_key_range(mod->core_layout.base, mod->core_layout.size);
+	dept_free_range(mod->core_layout.base, mod->core_layout.size);
 
 	module_deallocate(mod, info);
  free_copy:
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 51efaab..5784b07 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6285,6 +6285,14 @@ static void __sched notrace __schedule(unsigned int sched_mode)
 	rcu_note_context_switch(!!sched_mode);
 
 	/*
+	 * Skip the commit if the current task does not actually go to
+	 * sleep.
+	 */
+	if (READ_ONCE(prev->__state) & TASK_NORMAL &&
+	    sched_mode == SM_NONE)
+		dept_ask_event_wait_commit(_RET_IP_);
+
+	/*
 	 * Make sure that signal_pending_state()->signal_pending() below
 	 * can't be reordered with __set_current_state(TASK_INTERRUPTIBLE)
 	 * done by the caller to avoid the race with signal_wake_up():
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 075cd25..3c17507 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1261,6 +1261,33 @@ config DEBUG_PREEMPT
 
 menu "Lock Debugging (spinlocks, mutexes, etc...)"
 
+config DEPT
+	bool "Dependency tracking"
+	depends on DEBUG_KERNEL && LOCK_DEBUGGING_SUPPORT
+	select DEBUG_SPINLOCK
+	select DEBUG_MUTEXES
+	select DEBUG_RT_MUTEXES if RT_MUTEXES
+	select DEBUG_RWSEMS
+	select DEBUG_WW_MUTEX_SLOWPATH
+	select DEBUG_LOCK_ALLOC
+	select TRACE_IRQFLAGS
+	select STACKTRACE
+	select FRAME_POINTER if !MIPS && !PPC && !ARM && !S390 && !MICROBLAZE && !ARC && !X86
+	select KALLSYMS
+	select KALLSYMS_ALL
+	select PROVE_LOCKING
+	default n
+	help
+	  Check dependencies between wait and event and report it if
+	  deadlock possibility has been detected. Multiple reports are
+	  allowed if there are more than a single problem.
+
+	  This feature is considered EXPERIMENTAL that might produce
+	  false positive reports because new dependencies start to be
+	  tracked, that have never been tracked before. It's worth
+	  noting, to mitigate the impact by the false positives, multi
+	  reporting has been supported.
+
 config LOCK_DEBUGGING_SUPPORT
 	bool
 	depends on TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT
-- 
1.9.1