linux-kernel - Re: WARNING in shmem_evict

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Date:	Wed, 16 Dec 2015 20:23:11 +0100
From:	Holger Hoffstätte 
	<holger.hoffstaette@...glemail.com>
To:	Hugh Dickins <hughd@...gle.com>, Dmitry Vyukov <dvyukov@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	syzkaller <syzkaller@...glegroups.com>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Greg Thelen <gthelen@...gle.com>
Subject: Re: WARNING in shmem_evict_inode

On 12/02/15 10:29, Hugh Dickins wrote:
> On Mon, 23 Nov 2015, Dmitry Vyukov wrote:
>> On Mon, Nov 9, 2015 at 9:55 AM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
[snip]
>>> triggers WARNING in shmem_evict_inode:
>>>
>>> ------------[ cut here ]------------
>>> WARNING: CPU: 0 PID: 10442 at mm/shmem.c:625 shmem_evict_inode+0x335/0x480()
>>> Modules linked in:
>>> CPU: 1 PID: 8944 Comm: executor Not tainted 4.3.0+ #39
>>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>>>  00000000ffffffff ffff88006c6afab8 ffffffff81aad406 0000000000000000
>>>  ffff88006e39ac80 ffffffff83091660 ffff88006c6afaf8 ffffffff81100829
>>>  ffffffff814192e5 ffffffff83091660 0000000000000271 ffff88003d075aa8
>>> Call Trace:
>>>  [<ffffffff81100a59>] warn_slowpath_null+0x29/0x30 kernel/panic.c:480
>>>  [<ffffffff814192e5>] shmem_evict_inode+0x335/0x480 mm/shmem.c:625
>>>  [<ffffffff8151560e>] evict+0x26e/0x580 fs/inode.c:542
>>>  [<     inline     >] iput_final fs/inode.c:1477
[snip]
> It was more interesting than I expected, thanks.
> I believe you will find that this fixes it.
> 
> [PATCH] tmpfs: fix shmem_evict_inode warnings on i_blocks

Since I just saw this in Linus' tree, here's another retrospective bug
report and Thank You for fixing it. :-)

The problem is quite real, even though I'm probably the only other person
to ever report it, see: http://www.spinics.net/lists/linux-fsdevel/msg83567.html

> Cc stable?  I don't think that's necessary, but might be proved wrong:
> along with the warning, the bug does allow one page beyond the limit
> to be allocated from a size-limited tmpfs mount.

It applies and works fine, so it probably wouldn't hurt. I'm using it in my
4.1++ tree as we speak, no problems.

-h

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