linux-kernel - Re: linux-next: WARNING: at kernel/lockdep.c:2680 check

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Date:	Tue, 03 Jun 2008 18:28:09 +0200
From:	Johannes Weiner <hannes@...urebad.de>
To:	"Kevin Winchester" <kjwinchester@...il.com>
Cc:	"Peter Zijlstra" <a.p.zijlstra@...llo.nl>,
	"Ingo Molnar" <mingo@...hat.com>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: linux-next: WARNING: at kernel/lockdep.c:2680 check_flags+0x98/0x151()

Hi,

"Kevin Winchester" <kjwinchester@...il.com> writes:

> On Tue, Jun 3, 2008 at 5:53 AM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
>> On Mon, 2008-06-02 at 20:47 -0300, Kevin Winchester wrote:
>>> In next-20080530 and next-20080602 (and possibly earlier - I can't
>>> remember the linux-next tree before that I tried) I get the following:
>>>
>>> [   12.885153] ------------[ cut here ]------------
>>> [   12.885203] WARNING: at kernel/lockdep.c:2680 check_flags+0x98/0x151()
>>> [   12.885248] Pid: 4, comm: watchdog/0 Not tainted
>>> 2.6.26-rc4-next-20080602 #13
>>> [   12.885292]
>>> [   12.885293] Call Trace:
>>> [   12.885364]  [<ffffffff8022bbd5>] warn_on_slowpath+0x58/0x8a
>>> [   12.885410]  [<ffffffff804c9cfe>] ? _spin_unlock_irqrestore+0x51/0x6d
>>> [   12.885455]  [<ffffffff8032ff41>] ? debug_locks_off+0x9/0x3c
>>> [   12.885498]  [<ffffffff802582dd>] ? ftrace_record_ip+0x1fa/0x272
>>> [   12.885542]  [<ffffffff8025278a>] ? watchdog+0xc5/0x1ff
>>> [   12.885584]  [<ffffffff8020b2c0>] ? mcount_call+0x5/0x35
>>> [   12.885627]  [<ffffffff8025278a>] ? watchdog+0xc5/0x1ff
>>> [   12.885668]  [<ffffffff80247c80>] check_flags+0x98/0x151
>>> [   12.885710]  [<ffffffff8024ae72>] lock_acquire+0x4a/0xa9
>>> [   12.885753]  [<ffffffff8025278a>] ? watchdog+0xc5/0x1ff
>>> [   12.885795]  [<ffffffff802526c5>] ? watchdog+0x0/0x1ff
>>> [   12.885837]  [<ffffffff804c98da>] _read_lock+0x37/0x43
>>> [   12.885879]  [<ffffffff8025278a>] watchdog+0xc5/0x1ff
>>> [   12.885921]  [<ffffffff802526c5>] ? watchdog+0x0/0x1ff
>>> [   12.885963]  [<ffffffff8023e48b>] kthread+0x4e/0x7b
>>> [   12.886005]  [<ffffffff8020bf18>] child_rip+0xa/0x12
>>> [   12.886046]  [<ffffffff80227d8f>] ? finish_task_switch+0x57/0x92
>>> [   12.886090]  [<ffffffff804c9d55>] ? _spin_unlock_irq+0x3b/0x57
>>> [   12.886133]  [<ffffffff8020bad3>] ? restore_args+0x0/0x30
>>> [   12.886137]  [<ffffffff8023e43d>] ? kthread+0x0/0x7b
>>> [   12.886137]  [<ffffffff8020bf0e>] ? child_rip+0x0/0x12
>>> [   12.886137]
>>> [   12.886137] ---[ end trace 60e7f098a6913839 ]---
>>> [   12.886137] possible reason: unannotated irqs-on.
>>> [   12.886137] irq event stamp: 20
>>> [   12.886137] hardirqs last  enabled at (19): [<ffffffff80249cc3>]
>>> trace_hardirqs_on+0xd/0xf
>>> [   12.886137] hardirqs last disabled at (20): [<ffffffff80248565>]
>>> trace_hardirqs_off+0xd/0xf
>>> [   12.886137] softirqs last  enabled at (0): [<ffffffff80229fef>]
>>> copy_process+0x2da/0x109e
>>> [   12.886137] softirqs last disabled at (0): [<0000000000000000>] 0x0
>>>
>>> Do I understand this correctly that something enabled irqs in a way that
>>> got around lockdep?  I assume the problem is not in watchdog, just that
>>> the watchdog was the next thing to run that interacted with irqs and
>>> thus lockdep picked up the situation then?
>>>
>>> Is there additional debugging I can do, given some instructions?  If the
>>> cause is readily apparent to anyone, could they let me know (for my own
>>> interest) why it is apparent so that I can investigate things like this
>>> further next time?
>>
>>
>> You are correct - someone did sti but failed to call
>> trace_hardirqs_on(). Frequently its possible to isolate the code from
>> knowing the last recorded event:
>>
>> [   12.886137] irq event stamp: 20
>> [   12.886137] hardirqs last disabled at (20): [<ffffffff80248565>] trace_hardirqs_off+0xd/0xf
>>
>> However your compilation seems to have lost the caller IP:
>>
>> void trace_hardirqs_off(void)
>> {
>>        trace_hardirqs_off_caller(CALLER_ADDR0);
>> }
>> EXPORT_SYMBOL(trace_hardirqs_off);
>>
>> So that is of little help here. (Not sure how that happened, nor how you
>> could fix that - perhaps turn on some debugging knobs like build with
>> debug info etc..)
>>
>
> Could this be related to CONFIG_CC_OPTIMIZE_INLINING (or whatever it
> is called now)?  I am pretty sure I have that enabled.  I will check
> the rest of my config this evening to see if there is anything else I
> can turn on/off to help.
>
>>
>>> This is completely reproducible on every boot - should I try to bisect it?
>>
>> That is a possibility yes - if you can find the offending patch it
>> should be relatively straight forward to find the offending sti.
>>
>
> Sure - I can try it this evening.  Also, is calling sti the only way
> this could have happened?  And is linux-next broken out into a single
> patch?  I wouldn't expect there to be too many calls to sti, so a grep
> in the patch file might be quicker than bisection.

git-log -p origin/master..next/master showed nothing interesting.
Grepping for sti() would also not find indirect calls.

	Hannes
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