linux-kernel - Re: [PATCH] mm: memcg/slab: fix racy access to page->mem_cgroup in mem_cgroup_from

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Date:   Fri, 11 Sep 2020 15:40:20 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Roman Gushchin <guro@...com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Kernel Team <kernel-team@...com>,
        LKML <linux-kernel@...r.kernel.org>,
        Vlastimil Babka <vbabka@...e.cz>, stable@...r.kernel.org
Subject: Re: [PATCH] mm: memcg/slab: fix racy access to page->mem_cgroup in mem_cgroup_from_obj()

On Fri, Sep 11, 2020 at 2:34 PM Roman Gushchin <guro@...com> wrote:
>
[snip]
> >
> > Also have you taken a look at [1]? I am still trying to figure out how
> > that is possible.
> >
> > [1] https://lore.kernel.org/lkml/20200901075321.GL4299@shao2-debian/
>
> Hm, yeah, it's complicated. At the very first glance it looks like that the
> obj_cgroups vector is placed onto the very same page it describes, or at least
> it shares the kmem_cache with it, with some bad consequences. Could be something
> SLAB-specific, newer saw anything like that with SLUB.
> Or maybe it's completely unrelated and has been attributed to this commit
> by mistake.
>
> I've spent several hours running the provided test in a loop, but wasn't
> lucky enough to trigger it. Did you try?
>

Yeah same, no success in reproducing it.