Date:	Thu, 4 Feb 2010 01:43:53 +0300
From:	Alexander Beregalov <a.beregalov@...il.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: reiserfs deadlock

On 3 February 2010 23:29, Frederic Weisbecker <fweisbec@...il.com> wrote:
> On Wed, Feb 03, 2010 at 10:08:57PM +0300, Alexander Beregalov wrote:
>> On 3 February 2010 22:03, Alexander Beregalov <a.beregalov@...il.com> wrote:
>> > Hi Frederic
>> >
>> > I do not have previous messages and do not know how to reproduce it.
>> > Kernel was 2.6.33-rc5-00237-g9a3cbe3
>> >
>>
>> Hm, I have the same after reboot.
>>
>> Do you need me to do anything before I try to fsck ?
>
>
> Yeah. Rebooting again makes your kernel soft lockup?
Yes, reboot does not help. I even can't login, agetty and sshd are frozen.

INFO: task sshd:1863 blocked for more than 120 seconds.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
sshd          D 6f60ec44  6576  1863   1810 0x00000000
 f633dd78 00000046 ffffffff 6f60ec44 0000000f f7306b30 f73068b0 00000000
 f7306d84 7fffffff 00000000 f633de70 f633dde8 c134da45 00000000 f633dd8c
 c104ca3b 00000000 7fffffff 0000000f 6f618f50 f73068b0 00000000 00000000
Call Trace:
 [<c134da45>] schedule_timeout+0x125/0x1b0
 [<c104ca3b>] ? trace_hardirqs_off+0xb/0x10
 [<c1350152>] ? _raw_spin_unlock_irq+0x22/0x30
 [<c104e4c4>] ? trace_hardirqs_on_caller+0x124/0x170
 [<c104e51b>] ? trace_hardirqs_on+0xb/0x10
 [<c134d7d0>] wait_for_common+0xd0/0x130
 [<c1024850>] ? default_wake_function+0x0/0x10
 [<c134d8c2>] wait_for_completion+0x12/0x20
 [<c1039709>] call_usermodehelper_exec+0x89/0xb0
 [<c1039471>] ? call_usermodehelper_setup+0x71/0xb0
 [<c134d730>] ? wait_for_common+0x30/0x130
 [<c10398e2>] __request_module+0xa2/0xf0
 [<c10a6136>] ? new_inode+0x76/0x80
 [<c13501cd>] ? _raw_spin_unlock+0x1d/0x20
 [<c12cc89f>] __sock_create+0x18f/0x1f0
 [<c107b22a>] ? might_fault+0x4a/0xa0
 [<c12cc967>] sock_create+0x37/0x40
 [<c12ccb1e>] sys_socket+0x3e/0x70
 [<c12ccbb0>] sys_socketcall+0x60/0x270
 [<c1002b43>] ? sysenter_exit+0xf/0x18
 [<c11d5eb4>] ? trace_hardirqs_on_thunk+0xc/0x10
 [<c1002b10>] sysenter_do_call+0x12/0x36
no locks held by sshd/1863.

No locks - what does it mean?

>
> Usually such softlockup happens because we have a lock
> inversion, in which case you should have a lockdep report
> before the softlockup.

No, I do not have it. 120 seconds after boot I see these messages on
the console,
no lockdep reports (lockdep is enabled).

>
> Otherwise this can also happen when we wait for an event
> that needs the lock to complete but
> that can not happen because we already have the lock.
>
> Task A hold reiserfs lock and wait for event 1
> Task B wants to complete event 1 but it need the reisers lock
> for that => deadlock.
>
> This can usually be found in a softlockup report: lots of
> tasks are blocked on reiserfs_write_lock/mutex_lock
> except one, and this one is important as it is probably
> the waiter: the task that holds the lock and that is waiting
> for another event (that in turn needs the lock to complete).
>
> Having more reports could probably help us:
>
> echo 100 > /proc/sys/kernel/hung_task_warnings

Ok, I will modify rc scripts to do it, as I can't login.

>
> Hopefully you can still reproduce it :-s
>
> Thanks a lot!
>
>
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