Re: [PATCH] cgroup: missing rcu read lock around task_css_set

[Sasha Levin]

On 03/03/2014 06:00 PM, Sasha Levin wrote:
> 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.

Hi Tejun,

It bisects down to your patch: "cgroup: drop task_lock() protection around task->cgroups". I'll
look into it later unless it's obvious to you.


Thanks,
Sasha

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/