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

[Roman Gushchin]

On Tue, Feb 01, 2022 at 12:48:41PM -1000, Tejun Heo wrote:
> 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@xxxxxx>
> > Reported-by: Alexander Egorenkov <egorenar@xxxxxxxxxxxxx>
> > Tested-by: Alexander Egorenkov <egorenar@xxxxxxxxxxxxx>
> > Reviewed-by: Waiman Long <longman@xxxxxxxxxx>
> > Cc: Tejun Heo <tj@xxxxxxxxxx>
> > Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> > Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
> > Cc: Jeremy Linton <jeremy.linton@xxxxxxx>
> > Cc: cgroups@xxxxxxxxxxxxxxx
> 
> Acked-by: Tejun Heo <tj@xxxxxxxxxx>

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

I think so, usually this stuff goes through @mm.

Thanks!