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References: <1247725694-6082-6-git-send-email-fweisbec@gmail.com>
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Date: Wed, 22 Jul 2009 19:17:25 +0200
Message-ID: <c62985530907221017i427b1ae1s8cbb593106c658a1@mail.gmail.com>
Subject: Re: [tip:sched/core] sched: Pull up the might_sleep() check into 
	cond_resched()
From: =?ISO-8859-1?Q?Fr=E9d=E9ric_Weisbecker?= <fweisbec@gmail.com>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Li Zefan <lizf@cn.fujitsu.com>, hpa@zytor.com,
       linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@elte.hu,
       linux-tip-commits@vger.kernel.org
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2009/7/20 Peter Zijlstra <a.p.zijlstra@chello.nl>
>
> On Mon, 2009-07-20 at 04:12 -0400, Frederic Weisbecker wrote:
>
> > Hm, I can read that in fs/dcache.c:512
> >
> > /* dentry->d_lock was dropped in prune_one_dentry() */
> > cond_resched_lock(&dcache_lock);
>
> dentry->d_lock != dcache_lock
>
> > Isn't it a mususe of cond_resched_lock() ?
> > In this case, dcache.c should be fixed.
>
> Both sites look good wrt locking. So there's something else fishy.
>

(Resend in text/plain, sorry.)


Ah, I think I've got it. In case of !CONFIG_PREEMPT, the spinlocks of
course don't play
with preemption, making no change reflected in the preempt_count().
The assumption of preempt_count() = 1
is then false.

I prepare a patch.
Thanks.