[PATCH] cgroup: missing rcu read lock around task_css_set
Sasha Levin
sasha.levin at oracle.com
Mon Mar 3 23:00:25 UTC 2014
On 03/03/2014 05:45 PM, Tejun Heo wrote:
> On Mon, Mar 03, 2014 at 05:43:11PM -0500, Sasha Levin wrote:
>> On 03/03/2014 05:33 PM, Tejun Heo wrote:
>>> On Sat, Mar 01, 2014 at 10:00:11PM -0500, Sasha Levin wrote:
>>>> rcu read lock should be held when calling and working with task_css_set.
>>>>
>>>> This patch also fixes a related lockdep warning.
>>>
>>> Hmmm... PF_EXITING should be visible at that point and cset can't
>>> change anymore. We prolly need to update lockdep annotation rather
>>> than adding spurious rcu locking around it. Against which branch is
>>> it? Can you please post the lockdep warning?
>>
>> I see it on -next.
>
> I think the right thing to do is using task_css_set_check() with
> PF_EXITING check and add comment explaining that cset can no longer
> change. Can you please write up a patch?
Hrm... there is a PF_EXITING check there already:
#define task_css_set_check(task, __c) \
rcu_dereference_check((task)->cgroups, \
lockdep_is_held(&cgroup_mutex) || \
lockdep_is_held(&css_set_rwsem) || \
((task)->flags & PF_EXITING) || (__c))
I see it's not happening on Linus's master so I'll run a bisection to figure out what broke it.
Thanks,
Sasha
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