diff options
| author | Salman Qazi <sqazi@google.com> | 2012-06-14 23:55:30 +0200 |
|---|---|---|
| committer | Tejun Heo <tj@kernel.org> | 2012-06-19 00:38:02 +0200 |
| commit | 8e3bbf42c6d73881956863cc3305456afe2bc4ea (patch) | |
| tree | bb3369e7444a2efe8e890ddd341e576e3cba18c1 | |
| parent | cgroup: make sure that decisions in __css_put are atomic (diff) | |
| download | linux-8e3bbf42c6d73881956863cc3305456afe2bc4ea.tar.xz linux-8e3bbf42c6d73881956863cc3305456afe2bc4ea.zip | |
cgroups: Account for CSS_DEACT_BIAS in __css_put
When we fixed the race between atomic_dec and css_refcnt, we missed
the fact that css_refcnt internally subtracts CSS_DEACT_BIAS to get
the actual reference count. This can potentially cause a refcount leak
if __css_put races with cgroup_clear_css_refs.
Signed-off-by: Salman Qazi <sqazi@google.com>
Acked-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
| -rw-r--r-- | kernel/cgroup.c | 12 |
1 files changed, 10 insertions, 2 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c index ceeafe874b3f..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 */ @@ -4982,9 +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(); - switch (atomic_dec_return(&css->refcnt)) { + v = css_unbias_refcnt(atomic_dec_return(&css->refcnt)); + + switch (v) { case 1: if (notify_on_release(cgrp)) { set_bit(CGRP_RELEASABLE, &cgrp->flags); |