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Commit 2219449a authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: remove cgroup_lock_is_held() 



We don't want controllers to assume that the information is officially
available and do funky things with it.

The only user is task_subsys_state_check() which uses it to verify RCU
access context.  We can move cgroup_lock_is_held() inside
CONFIG_PROVE_RCU but that doesn't add meaningful protection compared
to conditionally exposing cgroup_mutex.

Remove cgroup_lock_is_held(), export cgroup_mutex iff CONFIG_PROVE_RCU
and use lockdep_is_held() directly on the mutex in
task_subsys_state_check().

While at it, add parentheses around macro arguments in
task_subsys_state_check().

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent 47cfcd09

include/linux/cgroup.h

+9 −4
Original line number Diff line number Diff line
@@ -30,7 +30,6 @@ struct css_id; 


extern int cgroup_init_early(void);

extern int cgroup_init(void);

extern int cgroup_lock_is_held(void);

extern void cgroup_fork(struct task_struct *p);

extern void cgroup_post_fork(struct task_struct *p);

extern void cgroup_exit(struct task_struct *p, int run_callbacks);
@@ -552,10 +551,16 @@ static inline struct cgroup_subsys_state *cgroup_subsys_state( 
 * rcu_dereference_check() conditions, such as locks used during the

 * cgroup_subsys::attach() methods.

 */

#ifdef CONFIG_PROVE_RCU

extern struct mutex cgroup_mutex;

#define task_subsys_state_check(task, subsys_id, __c)			\

	rcu_dereference_check(task->cgroups->subsys[subsys_id],		\

			      lockdep_is_held(&task->alloc_lock) ||	\

			      cgroup_lock_is_held() || (__c))

	rcu_dereference_check((task)->cgroups->subsys[(subsys_id)],	\

			      lockdep_is_held(&(task)->alloc_lock) ||	\

			      lockdep_is_held(&cgroup_mutex) || (__c))

#else

#define task_subsys_state_check(task, subsys_id, __c)			\

	rcu_dereference((task)->cgroups->subsys[(subsys_id)])

#endif



static inline struct cgroup_subsys_state *

task_subsys_state(struct task_struct *task, int subsys_id)

kernel/cgroup.c

+6 −14
Original line number Diff line number Diff line
@@ -83,7 +83,13 @@ 
 * B happens only through cgroup_show_options() and using cgroup_root_mutex

 * breaks it.

 */

#ifdef CONFIG_PROVE_RCU

DEFINE_MUTEX(cgroup_mutex);

EXPORT_SYMBOL_GPL(cgroup_mutex);	/* only for task_subsys_state_check() */

#else

static DEFINE_MUTEX(cgroup_mutex);

#endif



static DEFINE_MUTEX(cgroup_root_mutex);



/*
@@ -251,20 +257,6 @@ static int cgroup_destroy_locked(struct cgroup *cgrp); 
static int cgroup_addrm_files(struct cgroup *cgrp, struct cgroup_subsys *subsys,

			      struct cftype cfts[], bool is_add);



#ifdef CONFIG_PROVE_LOCKING

int cgroup_lock_is_held(void)

{

	return lockdep_is_held(&cgroup_mutex);

}

#else /* #ifdef CONFIG_PROVE_LOCKING */

int cgroup_lock_is_held(void)

{

	return mutex_is_locked(&cgroup_mutex);

}

#endif /* #else #ifdef CONFIG_PROVE_LOCKING */



EXPORT_SYMBOL_GPL(cgroup_lock_is_held);



static int css_unbias_refcnt(int refcnt)

{

	return refcnt >= 0 ? refcnt : refcnt - CSS_DEACT_BIAS;