Commit 8e3bbf42 authored by Salman Qazi's avatar Salman Qazi Committed by Tejun Heo

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: default avatarSalman Qazi <sqazi@google.com>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 967db0ea
......@@ -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);
......
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