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authorLinus Torvalds <torvalds@linux-foundation.org>2012-06-20 22:11:04 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-06-20 22:11:04 -0700
commit2ce5682947872061148b0e5ed2212e03d0d8bc8b (patch)
tree0038a1806eac265460c13c4b1f0cfa91822978e2 /kernel
parentc4c0e9e544a0eb640798cc66e68f394fa4a561bf (diff)
parent8e3bbf42c6d73881956863cc3305456afe2bc4ea (diff)
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
Diffstat (limited to 'kernel')
-rw-r--r--kernel/cgroup.c13
1 files changed, 10 insertions, 3 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 72fcd3069a90..2097684cf194 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -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);