Message-ID: <CAF1ivSa3i=4=sdD_ajdQ-fS-ifErFVDrOA1suLZTDG0BZ3TpZg@mail.gmail.com>
Date:	Wed, 14 Sep 2011 21:48:09 +0800
From:	Lin Ming <mlin@...pku.edu.cn>
To:	Simon Kirby <sim@...tway.ca>
Cc:	linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Fabio Coatti <fabio.coatti@...il.com>
Subject: Re: [3.1-rc4] vfs_rmdir() -> mutex_unlock() Oops

On Wed, Sep 14, 2011 at 12:43 AM, Simon Kirby <sim@...tway.ca> wrote:
> On Mon, Sep 12, 2011 at 03:17:00PM -0700, Simon Kirby wrote:
>
>> On Thu, Sep 08, 2011 at 03:24:20PM -0700, Simon Kirby wrote:
>>
>> > This box primarily does most of its VFS stuff over lots of NFS mounts,
>> > but has some local EXT3 filesystems. This has happened a couple of times:
>> >
>> > BUG: unable to handle kernel NULL pointer dereference at 00000000000000b8
>>...
>> Got a few more identical Oopses on another box running slightly past
>> 3.1-rc5 (79016f648872549392d232cd648bd02298c2d2bb). It seems to be
>> do_rmdir()'s mutex_unlock() call.
>>
>> I'm building -rc6 with CONFIG_DEBUG_MUTEXES now.
>
> ...and not much more help with CONFIG_DEBUG_MUTEXES, from 3.1-rc6:
>
> BUG: unable to handle kernel NULL pointer dereference at 00000000000000a4
> IP: [<ffffffff816adc93>] __mutex_unlock_slowpath+0x53/0x140
> PGD 13c6c4067 PUD 2256fc067 PMD 0
> Oops: 0002 [#1] SMP
> CPU 2
> Modules linked in: ipmi_devintf ipmi_si ipmi_msghandler xt_recent nf_conntrack_ftp xt_state xt_owner nf_conntrack_ipv4 nf_conntrack nf_defrag_ipv4 bnx2
>
> Pid: 27658, comm: php Not tainted 3.1.0-rc6-hw-mudbg+ #32 Dell Inc. PowerEdge 1950/0TT740
> RIP: 0010:[<ffffffff816adc93>]  [<ffffffff816adc93>] __mutex_unlock_slowpath+0x53/0x140
> RSP: 0018:ffff8800b65e1e28  EFLAGS: 00010046
> RAX: 0000000000000100 RBX: ffff88001bcece48 RCX: ffff88001bd05348
> RDX: 0000000040000200 RSI: ffff8800916cf6c0 RDI: 00000000000000a0
> RBP: ffff8800b65e1e48 R08: 00000000043205bc R09: ffffea00011340c0
> R10: 0000000000000000 R11: 0000000000000002 R12: 00000000000000a0
> R13: 00000000000000a4 R14: 0000000000000246 R15: 00007f7fe2d15680
> FS:  00007f7fe2e1f720(0000) GS:ffff88022fc80000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000000000a4 CR3: 0000000215c16000 CR4: 00000000000006e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> Process php (pid: 27658, threadinfo ffff8800b65e0000, task ffff8800175d4320)
> Stack:
>  ffff88001bcece48 00000000fffffffe ffff8800916cf6c0 00007f7fe2d146a8
>  ffff8800b65e1e58 ffffffff816add89 ffff8800b65e1e88 ffffffff8110ec70
>  ffff8800b65e1e98 ffff8800916cf6c0 ffff8800b65e1e98 0000000000000000
> Call Trace:
>  [<ffffffff816add89>] mutex_unlock+0x9/0x10
>  [<ffffffff8110ec70>] vfs_rmdir+0xb0/0x100
>  [<ffffffff8110ed96>] do_rmdir+0xd6/0x130
>  [<ffffffff81102063>] ? fput+0x1c3/0x260
>  [<ffffffff810fe648>] ? filp_close+0x68/0xa0
>  [<ffffffff8110ee41>] sys_rmdir+0x11/0x20
>  [<ffffffff816b6f3b>] system_call_fastpath+0x16/0x1b
> Code: 75 1b 65 48 8b 04 25 c8 b5 00 00 48 63 80 44 e0 ff ff a9 00 ff ff 07 0f 85 bb 00 00 00 9c 41 5e fa b8 00 01 00 00 4d 8d 6c 24 04 <f0> 66 41 0f c1 45 00 38 e0 74 08 f3 90 41 8a 45 00 eb f4 44 8b
> RIP  [<ffffffff816adc93>] __mutex_unlock_slowpath+0x53/0x140
>  RSP <ffff8800b65e1e28>
> CR2: 00000000000000a4
> ---[ end trace f515ec8376bdb799 ]---
>
> How can I further debug this? At this point, it seems to be happening several times daily.

Fabio reported a similar bug,
3.0.3 [BUG] unable to handle kernel NULL pointer dereference
http://marc.info/?t=131416920900001&r=1&w=2

Do you have a test case to trigger this bug reliably?

Lin Ming
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