Convert the functions that temporarily suppress RCU CPU
stall reporting:
rcu_sysrq_start()
rcu_sysrq_end()
to more generic functions that may be called by functions
other than the SysRq handler:
rcu_suppress_start()
rcu_suppress_end()
Covert the underlying variable:
rcu_cpu_stall_suppress
to an atomic variable so multiple threads can manipulate it at the
same time, incrementing it in start() and decrementing in end().
Expose that in sysfs in a read-only
/sys/module/rcupdate/parameters/rcu_cpu_stall_suppress_dyn
Keep
/sys/module/rcupdate/parameters/rcu_cpu_stall_suppress
as writeable by userspace, but OR that into the equations rather than
directly manipulate the atomic value.
Signed-off-by: Robert Elliott <elliott@xxxxxxx>
---
.../RCU/Design/Requirements/Requirements.rst | 6 +++---
Documentation/RCU/stallwarn.rst | 19 +++++++++++++++----
arch/parisc/kernel/process.c | 2 +-
drivers/tty/sysrq.c | 4 ++--
include/linux/rcupdate.h | 8 ++++----
kernel/rcu/rcu.h | 11 ++++++-----
kernel/rcu/tree_stall.h | 18 ++++++++++--------
kernel/rcu/update.c | 11 ++++++++++-
8 files changed, 51 insertions(+), 28 deletions(-)
diff --git a/Documentation/RCU/Design/Requirements/Requirements.rst b/Documentation/RCU/Design/Requirements/Requirements.rst
index 49387d823619..5083490bb6fc 100644
--- a/Documentation/RCU/Design/Requirements/Requirements.rst
+++ b/Documentation/RCU/Design/Requirements/Requirements.rst
@@ -1639,9 +1639,9 @@ against mishaps and misuse:
``rcupdate.rcu_cpu_stall_suppress`` to suppress the splats. This
kernel parameter may also be set via ``sysfs``. Furthermore, RCU CPU
stall warnings are counter-productive during sysrq dumps and during
- panics. RCU therefore supplies the rcu_sysrq_start() and
- rcu_sysrq_end() API members to be called before and after long
- sysrq dumps. RCU also supplies the rcu_panic() notifier that is
+ panics. RCU therefore supplies the rcu_suppress_start() and
+ rcu_suppress_end() API members to be called before and after long
+ CPU usage. RCU also supplies the rcu_panic() notifier that is
automatically invoked at the beginning of a panic to suppress further
RCU CPU stall warnings.
diff --git a/Documentation/RCU/stallwarn.rst b/Documentation/RCU/stallwarn.rst
index e38c587067fc..9e6fba72f56d 100644
--- a/Documentation/RCU/stallwarn.rst
+++ b/Documentation/RCU/stallwarn.rst
@@ -135,13 +135,24 @@ see include/trace/events/rcu.h.
Fine-Tuning the RCU CPU Stall Detector
======================================
-The rcuupdate.rcu_cpu_stall_suppress module parameter disables RCU's
-CPU stall detector, which detects conditions that unduly delay RCU grace
-periods. This module parameter enables CPU stall detection by default,
-but may be overridden via boot-time parameter or at runtime via sysfs.
+RCU's CPU stall detector detects conditions that unduly delay RCU grace
+periods. CPU stall detection is enabled by default, but may be overridden
+via boot-time parameter or at runtime via sysfs (accessible via
+/sys/module/rcupdate/parameters).
+
+The rcupdate.rcu_cpu_stall_suppress module parameter disables RCU's
+CPU stall detector.
+
+/sys/module/rcu_cpu_stall_suppress_dyn reports an internal semaphore
+used by the RCU's CPU stall detector. Functions holding a CPU for a
+long time (e.g., sysrq printouts) increment this value before use
+and decrement it when done, so the value reports the number of
+functions currently disabling stalls.
+
The stall detector's idea of what constitutes "unduly delayed" is
controlled by a set of kernel configuration variables and cpp macros:
+
CONFIG_RCU_CPU_STALL_TIMEOUT
----------------------------
diff --git a/arch/parisc/kernel/process.c b/arch/parisc/kernel/process.c
index c4f8374c7018..038378fe7bfa 100644
--- a/arch/parisc/kernel/process.c
+++ b/arch/parisc/kernel/process.c
@@ -126,7 +126,7 @@ void machine_power_off(void)
"Please power this system off now.");
/* prevent soft lockup/stalled CPU messages for endless loop. */
- rcu_sysrq_start();
+ rcu_suppress_start();
lockup_detector_soft_poweroff();
for (;;);
}
diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index d2b2720db6ca..81ab63a473a7 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -579,7 +579,7 @@ void __handle_sysrq(int key, bool check_mask)
orig_suppress_printk = suppress_printk;
suppress_printk = 0;
- rcu_sysrq_start();
+ rcu_suppress_start();
rcu_read_lock();
/*
* Raise the apparent loglevel to maximum so that the sysrq header
@@ -623,7 +623,7 @@ void __handle_sysrq(int key, bool check_mask)
console_loglevel = orig_log_level;
}
rcu_read_unlock();
- rcu_sysrq_end();
+ rcu_suppress_end();
suppress_printk = orig_suppress_printk;
}
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 03abf883a281..c0d8a4aae7ff 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -131,11 +131,11 @@ static inline void rcu_init_tasks_generic(void) { }
#endif
#ifdef CONFIG_RCU_STALL_COMMON
-void rcu_sysrq_start(void);
-void rcu_sysrq_end(void);
+void rcu_suppress_start(void);
+void rcu_suppress_end(void);
#else /* #ifdef CONFIG_RCU_STALL_COMMON */
-static inline void rcu_sysrq_start(void) { }
-static inline void rcu_sysrq_end(void) { }
+static inline void rcu_suppress_start(void) { }
+static inline void rcu_suppress_end(void) { }
#endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */
#if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_KVM_XFER_TO_GUEST_WORK))
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index c5aa934de59b..a658955a1174 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -224,24 +224,25 @@ extern int rcu_cpu_stall_ftrace_dump;
extern int rcu_cpu_stall_suppress;
extern int rcu_cpu_stall_timeout;
extern int rcu_exp_cpu_stall_timeout;
+extern atomic_t rcu_cpu_stall_suppress_dyn;
int rcu_jiffies_till_stall_check(void);
int rcu_exp_jiffies_till_stall_check(void);
static inline bool rcu_stall_is_suppressed(void)
{
- return rcu_stall_is_suppressed_at_boot() || rcu_cpu_stall_suppress;
+ return rcu_stall_is_suppressed_at_boot() ||
+ rcu_cpu_stall_suppress ||
+ atomic_read(&rcu_cpu_stall_suppress_dyn);
}
#define rcu_ftrace_dump_stall_suppress() \
do { \
- if (!rcu_cpu_stall_suppress) \
- rcu_cpu_stall_suppress = 3; \
+ atomic_inc(&rcu_cpu_stall_suppress_dyn); \
} while (0)
#define rcu_ftrace_dump_stall_unsuppress() \
do { \
- if (rcu_cpu_stall_suppress == 3) \
- rcu_cpu_stall_suppress = 0; \
+ atomic_dec(&rcu_cpu_stall_suppress_dyn); \
} while (0)
#else /* #endif #ifdef CONFIG_RCU_STALL_COMMON */
diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index 5653560573e2..260748bc5bc8 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -103,23 +103,25 @@ bool rcu_gp_might_be_stalled(void)
return !time_before(j, READ_ONCE(rcu_state.gp_start) + d);
}
-/* Don't do RCU CPU stall warnings during long sysrq printouts. */
-void rcu_sysrq_start(void)
+/* Don't do RCU CPU stall warnings during functions holding the CPU
+ * for a long period of time such as long sysrq printouts.
+ */
+void rcu_suppress_start(void)
{
- if (!rcu_cpu_stall_suppress)
- rcu_cpu_stall_suppress = 2;
+ atomic_inc(&rcu_cpu_stall_suppress_dyn);
}
+EXPORT_SYMBOL_GPL(rcu_suppress_start);
-void rcu_sysrq_end(void)
+void rcu_suppress_end(void)
{
- if (rcu_cpu_stall_suppress == 2)
- rcu_cpu_stall_suppress = 0;
+ atomic_dec(&rcu_cpu_stall_suppress_dyn);
}
+EXPORT_SYMBOL_GPL(rcu_suppress_end);
/* Don't print RCU CPU stall warnings during a kernel panic. */
static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
{
- rcu_cpu_stall_suppress = 1;
+ atomic_inc(&rcu_cpu_stall_suppress_dyn);
return NOTIFY_DONE;
}
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index f5e6a2f95a2a..ceee9d777384 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -501,11 +501,18 @@ EXPORT_SYMBOL_GPL(rcutorture_sched_setaffinity);
#ifdef CONFIG_RCU_STALL_COMMON
int rcu_cpu_stall_ftrace_dump __read_mostly;
module_param(rcu_cpu_stall_ftrace_dump, int, 0644);
-int rcu_cpu_stall_suppress __read_mostly; // !0 = suppress stall warnings.
+
+int rcu_cpu_stall_suppress __read_mostly; // !0 = suppress stall warnings from sysfs
EXPORT_SYMBOL_GPL(rcu_cpu_stall_suppress);
module_param(rcu_cpu_stall_suppress, int, 0644);
+
+atomic_t rcu_cpu_stall_suppress_dyn __read_mostly; // !0 = suppress stall warnings from functions
+EXPORT_SYMBOL_GPL(rcu_cpu_stall_suppress_dyn);
+module_param_named(rcu_cpu_stall_suppress_dyn, rcu_cpu_stall_suppress_dyn.counter, int, 0444);
+
int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;
module_param(rcu_cpu_stall_timeout, int, 0644);
+
int rcu_exp_cpu_stall_timeout __read_mostly = CONFIG_RCU_EXP_CPU_STALL_TIMEOUT;
module_param(rcu_exp_cpu_stall_timeout, int, 0644);
#endif /* #ifdef CONFIG_RCU_STALL_COMMON */
@@ -616,6 +623,8 @@ void __init rcupdate_announce_bootup_oddness(void)
pr_info("\tAll grace periods are expedited (rcu_expedited).\n");
if (rcu_cpu_stall_suppress)
pr_info("\tRCU CPU stall warnings suppressed (rcu_cpu_stall_suppress).\n");
+ if (atomic_read(&rcu_cpu_stall_suppress_dyn))
+ pr_info("\tDynamic RCU CPU stall warnings suppressed (rcu_cpu_stall_suppress_dyn).\n");
if (rcu_cpu_stall_timeout != CONFIG_RCU_CPU_STALL_TIMEOUT)
pr_info("\tRCU CPU stall warnings timeout set to %d (rcu_cpu_stall_timeout).\n", rcu_cpu_stall_timeout);
rcu_tasks_bootup_oddness();
--
2.38.1
