>From 6ab428604f724cf217a47b7d3f3353aab815b40e Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@xxxxxxxxxx>
Date: Fri, 28 Oct 2022 10:45:44 -1000
Subject: [PATCH] cgroup: Implement DEBUG_CGROUP_REF
It's really difficult to debug when cgroup or css refs leak. Let's add a
debug option to force the refcnt function to not be inlined so that they can
be kprobed for debugging.
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
Oops, forgot the cgroups ML. Resending. Patch is applied to
cgroup/for-6.1-fixes.
Thanks.
include/linux/cgroup.h | 97 +++++------------------------------
include/linux/cgroup_refcnt.h | 90 ++++++++++++++++++++++++++++++++
kernel/cgroup/cgroup.c | 5 ++
lib/Kconfig.debug | 10 ++++
4 files changed, 117 insertions(+), 85 deletions(-)
create mode 100644 include/linux/cgroup_refcnt.h
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index a88de5bdeaa9..5c9c07a44706 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -309,71 +309,23 @@ void css_task_iter_end(struct css_task_iter *it);
* Inline functions.
*/
+#ifdef CONFIG_DEBUG_CGROUP_REF
+void css_get(struct cgroup_subsys_state *css);
+void css_get_many(struct cgroup_subsys_state *css, unsigned int n);
+bool css_tryget(struct cgroup_subsys_state *css);
+bool css_tryget_online(struct cgroup_subsys_state *css);
+void css_put(struct cgroup_subsys_state *css);
+void css_put_many(struct cgroup_subsys_state *css, unsigned int n);
+#else
+#define CGROUP_REF_FN_ATTRS static inline
+#include <linux/cgroup_refcnt.h>
+#endif
+
static inline u64 cgroup_id(const struct cgroup *cgrp)
{
return cgrp->kn->id;
}
-/**
- * css_get - obtain a reference on the specified css
- * @css: target css
- *
- * The caller must already have a reference.
- */
-static inline void css_get(struct cgroup_subsys_state *css)
-{
- if (!(css->flags & CSS_NO_REF))
- percpu_ref_get(&css->refcnt);
-}
-
-/**
- * css_get_many - obtain references on the specified css
- * @css: target css
- * @n: number of references to get
- *
- * The caller must already have a reference.
- */
-static inline void css_get_many(struct cgroup_subsys_state *css, unsigned int n)
-{
- if (!(css->flags & CSS_NO_REF))
- percpu_ref_get_many(&css->refcnt, n);
-}
-
-/**
- * css_tryget - try to obtain a reference on the specified css
- * @css: target css
- *
- * Obtain a reference on @css unless it already has reached zero and is
- * being released. This function doesn't care whether @css is on or
- * offline. The caller naturally needs to ensure that @css is accessible
- * but doesn't have to be holding a reference on it - IOW, RCU protected
- * access is good enough for this function. Returns %true if a reference
- * count was successfully obtained; %false otherwise.
- */
-static inline bool css_tryget(struct cgroup_subsys_state *css)
-{
- if (!(css->flags & CSS_NO_REF))
- return percpu_ref_tryget(&css->refcnt);
- return true;
-}
-
-/**
- * css_tryget_online - try to obtain a reference on the specified css if online
- * @css: target css
- *
- * Obtain a reference on @css if it's online. The caller naturally needs
- * to ensure that @css is accessible but doesn't have to be holding a
- * reference on it - IOW, RCU protected access is good enough for this
- * function. Returns %true if a reference count was successfully obtained;
- * %false otherwise.
- */
-static inline bool css_tryget_online(struct cgroup_subsys_state *css)
-{
- if (!(css->flags & CSS_NO_REF))
- return percpu_ref_tryget_live(&css->refcnt);
- return true;
-}
-
/**
* css_is_dying - test whether the specified css is dying
* @css: target css
@@ -394,31 +346,6 @@ static inline bool css_is_dying(struct cgroup_subsys_state *css)
return !(css->flags & CSS_NO_REF) && percpu_ref_is_dying(&css->refcnt);
}
-/**
- * css_put - put a css reference
- * @css: target css
- *
- * Put a reference obtained via css_get() and css_tryget_online().
- */
-static inline void css_put(struct cgroup_subsys_state *css)
-{
- if (!(css->flags & CSS_NO_REF))
- percpu_ref_put(&css->refcnt);
-}
-
-/**
- * css_put_many - put css references
- * @css: target css
- * @n: number of references to put
- *
- * Put references obtained via css_get() and css_tryget_online().
- */
-static inline void css_put_many(struct cgroup_subsys_state *css, unsigned int n)
-{
- if (!(css->flags & CSS_NO_REF))
- percpu_ref_put_many(&css->refcnt, n);
-}
-
static inline void cgroup_get(struct cgroup *cgrp)
{
css_get(&cgrp->self);
diff --git a/include/linux/cgroup_refcnt.h b/include/linux/cgroup_refcnt.h
new file mode 100644
index 000000000000..1aa89295dac0
--- /dev/null
+++ b/include/linux/cgroup_refcnt.h
@@ -0,0 +1,90 @@
+/**
+ * css_get - obtain a reference on the specified css
+ * @css: target css
+ *
+ * The caller must already have a reference.
+ */
+CGROUP_REF_FN_ATTRS
+void css_get(struct cgroup_subsys_state *css)
+{
+ if (!(css->flags & CSS_NO_REF))
+ percpu_ref_get(&css->refcnt);
+}
+
+/**
+ * css_get_many - obtain references on the specified css
+ * @css: target css
+ * @n: number of references to get
+ *
+ * The caller must already have a reference.
+ */
+CGROUP_REF_FN_ATTRS
+void css_get_many(struct cgroup_subsys_state *css, unsigned int n)
+{
+ if (!(css->flags & CSS_NO_REF))
+ percpu_ref_get_many(&css->refcnt, n);
+}
+
+/**
+ * css_tryget - try to obtain a reference on the specified css
+ * @css: target css
+ *
+ * Obtain a reference on @css unless it already has reached zero and is
+ * being released. This function doesn't care whether @css is on or
+ * offline. The caller naturally needs to ensure that @css is accessible
+ * but doesn't have to be holding a reference on it - IOW, RCU protected
+ * access is good enough for this function. Returns %true if a reference
+ * count was successfully obtained; %false otherwise.
+ */
+CGROUP_REF_FN_ATTRS
+bool css_tryget(struct cgroup_subsys_state *css)
+{
+ if (!(css->flags & CSS_NO_REF))
+ return percpu_ref_tryget(&css->refcnt);
+ return true;
+}
+
+/**
+ * css_tryget_online - try to obtain a reference on the specified css if online
+ * @css: target css
+ *
+ * Obtain a reference on @css if it's online. The caller naturally needs
+ * to ensure that @css is accessible but doesn't have to be holding a
+ * reference on it - IOW, RCU protected access is good enough for this
+ * function. Returns %true if a reference count was successfully obtained;
+ * %false otherwise.
+ */
+CGROUP_REF_FN_ATTRS
+bool css_tryget_online(struct cgroup_subsys_state *css)
+{
+ if (!(css->flags & CSS_NO_REF))
+ return percpu_ref_tryget_live(&css->refcnt);
+ return true;
+}
+
+/**
+ * css_put - put a css reference
+ * @css: target css
+ *
+ * Put a reference obtained via css_get() and css_tryget_online().
+ */
+CGROUP_REF_FN_ATTRS
+void css_put(struct cgroup_subsys_state *css)
+{
+ if (!(css->flags & CSS_NO_REF))
+ percpu_ref_put(&css->refcnt);
+}
+
+/**
+ * css_put_many - put css references
+ * @css: target css
+ * @n: number of references to put
+ *
+ * Put references obtained via css_get() and css_tryget_online().
+ */
+CGROUP_REF_FN_ATTRS
+void css_put_many(struct cgroup_subsys_state *css, unsigned int n)
+{
+ if (!(css->flags & CSS_NO_REF))
+ percpu_ref_put_many(&css->refcnt, n);
+}
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index d922773fa90b..f786c4c973a0 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -248,6 +248,11 @@ static int cgroup_addrm_files(struct cgroup_subsys_state *css,
struct cgroup *cgrp, struct cftype cfts[],
bool is_add);
+#ifdef CONFIG_DEBUG_CGROUP_REF
+#define CGROUP_REF_FN_ATTRS noinline
+#include <linux/cgroup_refcnt.h>
+#endif
+
/**
* cgroup_ssid_enabled - cgroup subsys enabled test by subsys ID
* @ssid: subsys ID of interest
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 3761118d1879..b620a340d7df 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1701,6 +1701,16 @@ config LATENCYTOP
Enable this option if you want to use the LatencyTOP tool
to find out which userspace is blocking on what kernel operations.
+config DEBUG_CGROUP_REF
+ bool "Disable inlining of cgroup css reference count functions"
+ depends on DEBUG_KERNEL
+ depends on CGROUPS
+ depends on KPROBES
+ default n
+ help
+ Force cgroup css reference count functions to not be inlined so
+ that they can be kprobed for debugging.
+
source "kernel/trace/Kconfig"
config PROVIDE_OHCI1394_DMA_INIT
--
2.38.0
