commit: 967db0ea65b0bf8507a7643ac8f296c4f2c0a834 From: Salman Qazi <[email protected]> Date: Wed, 6 Jun 2012 18:51:35 -0700 Subject: cgroup: make sure that decisions in __css_put are atomic
__css_put is using atomic_dec on the ref count, and then looking at the ref count to make decisions. This is prone to races, as someone else may decrement ref count between our decrement and our decision. Instead, we should base our decisions on the value that we decremented the ref count to. (This results in an actual race on Google's kernel which I haven't been able to reproduce on the upstream kernel. Having said that, it's still incorrect by inspection). Signed-off-by: Salman Qazi <[email protected]> Acked-by: Li Zefan <[email protected]> Signed-off-by: Tejun Heo <[email protected]> Cc: [email protected] --- kernel/cgroup.c | 3 +-- 1 files changed, 1 insertions(+), 2 deletions(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 72fcd30..ceeafe8 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -4984,8 +4984,7 @@ void __css_put(struct cgroup_subsys_state *css) struct cgroup *cgrp = css->cgroup; rcu_read_lock(); - atomic_dec(&css->refcnt); - switch (css_refcnt(css)) { + switch (atomic_dec_return(&css->refcnt)) { case 1: if (notify_on_release(cgrp)) { set_bit(CGRP_RELEASABLE, &cgrp->flags); -- 1.7.3.4 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
