Re: [PATCH for-5.2-fixes] memcg: Don't loop on css_tryget_online() failure

[Tejun Heo <tj@kernel.org>]

On Wed, Jun 05, 2019 at 02:55:20PM +0200, Michal Hocko wrote:
> On Wed 29-05-19 14:06:17, Tejun Heo wrote:
> > A PF_EXITING task may stay associated with an offline css.
> > get_mem_cgroup_from_mm() may deadlock if mm->owner is in such state.
> > All similar logics in memcg are falling back to root memcg on
> > tryget_online failure and get_mem_cgroup_from_mm() can do the same.
> >
> > A similar failure existed for task_get_css() and could be triggered
> > through BSD process accounting racing against memcg offlining.  See
> > 18fa84a2db0e ("cgroup: Use css_tryget() instead of css_tryget_online()
> > in task_get_css()") for details.
> > 
> > Signed-off-by: Tejun Heo <tj@kernel.org>
> 
> Do we need to mark this patch for stable or this is too unlikely to
> happen?

This one's a lot less likely than the one in task_get_css() which
already is pretty low frequency.  I don't think it warrants -stable
tagging.

Thanks.

-- 
tejun