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From: Shakeel Butt <shakeelb@google.com>
To: Roman Gushchin <guro@fb.com>
Cc: Ming Lei <ming.lei@redhat.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	"Theodore Y . Ts'o" <tytso@mit.edu>, Jens Axboe <axboe@kernel.dk>,
	Ext4 Developers List <linux-ext4@vger.kernel.org>,
	linux-block <linux-block@vger.kernel.org>,
	Vlastimil Babka <vbabka@suse.cz>, Linux MM <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: REGRESSION: 37f4a24c2469: blk-mq: centralise related handling into blk_mq_get_driver_tag
Date: Fri, 25 Sep 2020 14:18:48 -0700	[thread overview]
Message-ID: <CALvZod5ETbjn7Y0A619Sd+sFO_9QCnUDC-_pBXPgq9AkAK0LRQ@mail.gmail.com> (raw)
In-Reply-To: <20200925205604.GA2228989@carbon.dhcp.thefacebook.com>

On Fri, Sep 25, 2020 at 1:56 PM Roman Gushchin <guro@fb.com> wrote:
>
> On Fri, Sep 25, 2020 at 12:19:02PM -0700, Shakeel Butt wrote:
> > On Fri, Sep 25, 2020 at 10:58 AM Shakeel Butt <shakeelb@google.com>
> > wrote:
> > >
> > [snip]
> > >
> > > I don't think you can ignore the flushing. The __free_once() in
> > > ___cache_free() assumes there is a space available.
> > >
> > > BTW do_drain() also have the same issue.
> > >
> > > Why not move slabs_destroy() after we update ac->avail and memmove()?
> >
> > Ming, can you please try the following patch?
> >
> >
> > From: Shakeel Butt <shakeelb@google.com>
> >
> > [PATCH] mm: slab: fix potential infinite recursion in ___cache_free
> >
> > With the commit 10befea91b61 ("mm: memcg/slab: use a single set of
> > kmem_caches for all allocations"), it becomes possible to call kfree()
> > from the slabs_destroy(). However if slabs_destroy() is being called for
> > the array_cache of the local CPU then this opens the potential scenario
> > of infinite recursion because kfree() called from slabs_destroy() can
> > call slabs_destroy() with the same array_cache of the local CPU. Since
> > the array_cache of the local CPU is not updated before calling
> > slabs_destroy(), it will try to free the same pages.
> >
> > To fix the issue, simply update the cache before calling
> > slabs_destroy().
> >
> > Signed-off-by: Shakeel Butt <shakeelb@google.com>
>
> I like the patch and I think it should fix the problem.
>
> However the description above should be likely asjusted a bit.
> It seems that the problem is not necessary caused by an infinite recursion,
> it can be even simpler.
>
> In cache_flusharray() we rely on the state of ac, which is described
> by ac->avail. In particular we rely on batchcount < ac->avail,
> as we shift the batchcount number of pointers by memmove.
> But if slabs_destroy() is called before and leaded to a change of the
> ac state, it can lead to a memory corruption.
>
> Also, unconditionally resetting ac->avail to 0 in do_drain() after calling
> to slab_destroy() seems to be wrong.
> It explains double free BUGs we've seen in stacktraces.
>

Yes, you are right. Let's first get this patch tested and after
confirmation we can update the commit message.

  reply	other threads:[~2020-09-25 21:19 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-03 23:02 [PATCH] ext4: flag as supporting buffered async reads Jens Axboe
2020-08-11 14:31 ` Jens Axboe
2020-08-18 18:11 ` Theodore Y. Ts'o
2020-08-18 18:12   ` Jens Axboe
2020-08-21 21:26     ` Jens Axboe
2020-08-22 14:33       ` Theodore Y. Ts'o
2020-08-22 15:48         ` Jens Axboe
2020-08-24 10:56           ` Jens Axboe
2020-08-25 14:18             ` Jens Axboe
2020-08-27  1:54               ` Jens Axboe
2020-09-04  0:10                 ` Jens Axboe
2020-09-04  3:55                   ` Theodore Y. Ts'o
2020-09-04 14:51                     ` Jens Axboe
2020-09-04 15:25                       ` Darrick J. Wong
2020-09-15  4:45                     ` REGRESSION: 37f4a24c2469: blk-mq: centralise related handling into blk_mq_get_driver_tag Theodore Y. Ts'o
2020-09-15  7:33                       ` Ming Lei
2020-09-15 22:45                         ` Theodore Y. Ts'o
2020-09-15 23:09                           ` Ming Lei
2020-09-16 20:20                             ` Theodore Y. Ts'o
2020-09-17  2:20                               ` Ming Lei
2020-09-17 14:30                                 ` Theodore Y. Ts'o
2020-09-17 23:08                                   ` Ming Lei
2020-09-24  0:59                                   ` Ming Lei
2020-09-24 14:33                                     ` Theodore Y. Ts'o
2020-09-25  1:13                                       ` Theodore Y. Ts'o
2020-09-25  7:31                                         ` Ming Lei
2020-09-25 16:19                                           ` Ming Lei
2020-09-25 16:32                                             ` Shakeel Butt
2020-09-25 16:47                                               ` Shakeel Butt
2020-09-25 17:22                                                 ` Roman Gushchin
2020-09-25 17:17                                             ` Linus Torvalds
2020-09-25 17:22                                               ` Shakeel Butt
2020-09-25 17:35                                                 ` Shakeel Butt
2020-09-25 17:47                                                   ` Roman Gushchin
2020-09-25 17:58                                                     ` Shakeel Butt
2020-09-25 19:19                                                       ` Shakeel Butt
2020-09-25 20:56                                                         ` Roman Gushchin
2020-09-25 21:18                                                           ` Shakeel Butt [this message]
2020-09-27 17:38                                                             ` Theodore Y. Ts'o
2020-09-26  1:43                                                         ` Ming Lei
2020-09-26  6:42                                                           ` Roman Gushchin
2020-09-25  1:14                                       ` Ming Lei
2020-09-25  2:34                                         ` Ming Lei
2020-10-02 20:08 ` [PATCH] ext4: flag as supporting buffered async reads Theodore Y. Ts'o
2020-10-02 20:10   ` Jens Axboe

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