Re: [PATCH RESEND] mm: memcg: synchronize objcg lists with a dedicated spinlock

[Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

On Tue, Feb 01, 2022 at 02:33:04PM -0800, Roman Gushchin wrote:
...
> In this example a slab allocation from __send_signal() caused a
> refilling and draining of a percpu objcg stock, resulted in a
> releasing of another non-related objcg. Objcg release path requires
> taking the css_set_lock, which is used to synchronize objcg lists.
> 
> This can create a circular dependency with the sighandler lock,
> which is taken with the locked css_set_lock by the freezer code
> (to freeze a task).
> 
> In general it seems that using css_set_lock to synchronize objcg lists
> makes any slab allocations and deallocation with the locked
> css_set_lock and any intervened locks risky.
> 
> To fix the problem and make the code more robust let's stop using
> css_set_lock to synchronize objcg lists and use a new dedicated
> spinlock instead.
> 
> Fixes: bf4f059954dc ("mm: memcg/slab: obj_cgroup API")
> Signed-off-by: Roman Gushchin <guro-b10kYP2dOMg@public.gmane.org>
> Reported-by: Alexander Egorenkov <egorenar-tEXmvtCZX7AybS5Ee8rs3A@public.gmane.org>
> Tested-by: Alexander Egorenkov <egorenar-tEXmvtCZX7AybS5Ee8rs3A@public.gmane.org>
> Reviewed-by: Waiman Long <longman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> Cc: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
> Cc: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
> Cc: Shakeel Butt <shakeelb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
> Cc: Jeremy Linton <jeremy.linton-5wv7dgnIgG8@public.gmane.org>
> Cc: cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org

Acked-by: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>

I suppose this will go through -mm? If you want me to route it through the
cgroup tree, please let me know.

Thanks.

-- 
tejun