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

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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
This commit is contained in:
Linus Torvalds 2012-06-20 22:11:04 -07:00
commit 2ce5682947
1 changed files with 10 additions and 3 deletions
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13
kernel/cgroup.c
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@ -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);