Commit 6ab42860 authored by Tejun Heo's avatar Tejun Heo
Browse files

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: default avatarTejun Heo <tj@kernel.org>
parent 79a818b5

include/linux/cgroup.h

+12 −85
Original line number Diff line number Diff line
@@ -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);

include/linux/cgroup_refcnt.h

0 → 100644
+90 −0
Original line number Diff line number Diff line 
/**

 * 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);

}

kernel/cgroup/cgroup.c

+5 −0
Original line number Diff line number Diff line
@@ -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

lib/Kconfig.debug

+10 −0
Original line number Diff line number Diff line
@@ -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