linux-kernel - Re: next-20090107: WARNING: at kernel/sched.c:4435 sub_preempt

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Message-ID: <f19298770901181024u63996912oa75fb76169b7e594@mail.gmail.com>
Date:	Sun, 18 Jan 2009 21:24:55 +0300
From:	Alexey Zaytsev <alexey.zaytsev@...il.com>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Laurent Riffard <laurent.riffard@...e.fr>,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: next-20090107: WARNING: at kernel/sched.c:4435 sub_preempt_count

On Sun, Jan 18, 2009 at 21:22, Alexey Zaytsev <alexey.zaytsev@...il.com> wrote:
> Hi.
>
> On Wed, Jan 14, 2009 at 05:00, Nick Piggin <npiggin@...e.de> wrote:
>> On Sun, Jan 11, 2009 at 03:49:45AM +0100, Ingo Molnar wrote:
>>>
>>> * Alexey Zaytsev <alexey.zaytsev@...il.com> wrote:
>>>
>>> > One more instance of http://marc.info/?l=linux-kernel&m=123134586202636&w=2
>>> > Added Ingo Molnar to CC.
>>>
>>> added Nick on Cc:. Nick, it's about:
>>>
>>> > commit 7317d7b87edb41a9135e30be1ec3f7ef817c53dd
>>> > Author: Nick Piggin <nickpiggin@...oo.com.au>
>>> > Date:   Tue Sep 30 20:50:27 2008 +1000
>>> >
>>> >    sched: improve preempt debugging
>>>
>>> causing a seemingly spurious warning.
>>
>> I don't know how it is spurious... Presumably the sequence _would_ have
>> caused preempt count to go negative if the bkl were not held...
>>
>> __do_softirq does a __local_bh_disable on entry, and it seems like the
>> _local_bh_enable on exit is what causes this warning. So something is
>> unbalanced somehow. Or is it some weird thing we do in early boot that
>> I am missing?
>>
>> Can you put in some printks around these functions in early boot to
>> get an idea of what preempt_count is doing?
>
> Sorry for the delay. I was busy and forgot about this issue.
> The warning does not show in -rc2 any more. Was it fixed, or
> just shadowed by something?
>

Uhg, right Ingo pushed his revert to Linus. Should have looked into
the changelog before posting, not after.
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