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Sender: Tejun Heo <htejun@gmail.com>
Date:   Tue, 1 Feb 2022 12:48:41 -1000
From:   Tejun Heo <tj@kernel.org>
To:     Roman Gushchin <guro@fb.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Alexander Egorenkov <egorenar@linux.ibm.com>,
        Waiman Long <longman@redhat.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Shakeel Butt <shakeelb@google.com>,
        Jeremy Linton <jeremy.linton@arm.com>, cgroups@vger.kernel.org
Subject: Re: [PATCH RESEND] mm: memcg: synchronize objcg lists with a
 dedicated spinlock
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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@fb.com>
> Reported-by: Alexander Egorenkov <egorenar@linux.ibm.com>
> Tested-by: Alexander Egorenkov <egorenar@linux.ibm.com>
> Reviewed-by: Waiman Long <longman@redhat.com>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Shakeel Butt <shakeelb@google.com>
> Cc: Jeremy Linton <jeremy.linton@arm.com>
> Cc: cgroups@vger.kernel.org

Acked-by: Tejun Heo <tj@kernel.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