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

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
...@@ -255,12 +255,17 @@ int cgroup_lock_is_held(void) ...@@ -255,12 +255,17 @@ int cgroup_lock_is_held(void)
EXPORT_SYMBOL_GPL(cgroup_lock_is_held); 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 */ /* the current nr of refs, always >= 0 whether @css is deactivated or not */
static int css_refcnt(struct cgroup_subsys_state *css) static int css_refcnt(struct cgroup_subsys_state *css)
{ {
int v = atomic_read(&css->refcnt); int v = atomic_read(&css->refcnt);
return v >= 0 ? v : v - CSS_DEACT_BIAS; return css_unbias_refcnt(v);
} }
/* convenient tests for these bits */ /* convenient tests for these bits */
...@@ -4982,10 +4987,12 @@ EXPORT_SYMBOL_GPL(__css_tryget); ...@@ -4982,10 +4987,12 @@ EXPORT_SYMBOL_GPL(__css_tryget);
void __css_put(struct cgroup_subsys_state *css) void __css_put(struct cgroup_subsys_state *css)
{ {
struct cgroup *cgrp = css->cgroup; struct cgroup *cgrp = css->cgroup;
int v;
rcu_read_lock(); rcu_read_lock();
atomic_dec(&css->refcnt); v = css_unbias_refcnt(atomic_dec_return(&css->refcnt));
switch (css_refcnt(css)) {
switch (v) {
case 1: case 1:
if (notify_on_release(cgrp)) { if (notify_on_release(cgrp)) {
set_bit(CGRP_RELEASABLE, &cgrp->flags); set_bit(CGRP_RELEASABLE, &cgrp->flags);
......
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