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Commit 2ce56829 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge branch 'for-3.5-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup 

Pull two cgroup fixes from Tejun Heo:
 "This containes two patches fixing a refcnt race bug during css_put().
  Decrementing and checking the value weren't atomic and two tasks could
  think that they both pushed the counter to zero."

* 'for-3.5-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  cgroups: Account for CSS_DEACT_BIAS in __css_put
  cgroup: make sure that decisions in __css_put are atomic
parents c4c0e9e5 8e3bbf42

kernel/cgroup.c

+10 −3
Original line number Diff line number Diff line
@@ -255,12 +255,17 @@ int cgroup_lock_is_held(void) 


EXPORT_SYMBOL_GPL(cgroup_lock_is_held);



static int css_unbias_refcnt(int refcnt)

{

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

}



/* the current nr of refs, always >= 0 whether @css is deactivated or not */

static int css_refcnt(struct cgroup_subsys_state *css)

{

	int v = atomic_read(&css->refcnt);



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

	return css_unbias_refcnt(v);

}



/* convenient tests for these bits */
@@ -4982,10 +4987,12 @@ EXPORT_SYMBOL_GPL(__css_tryget); 
void __css_put(struct cgroup_subsys_state *css)

{

	struct cgroup *cgrp = css->cgroup;

	int v;



	rcu_read_lock();

	atomic_dec(&css->refcnt);

	switch (css_refcnt(css)) {

	v = css_unbias_refcnt(atomic_dec_return(&css->refcnt));



	switch (v) {

	case 1:

		if (notify_on_release(cgrp)) {

			set_bit(CGRP_RELEASABLE, &cgrp->flags);