linux-kernel - Re: [tip:sched/core] sched: Pull up the might_sleep() check into cond

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Message-ID: <c62985530907221017i427b1ae1s8cbb593106c658a1@mail.gmail.com>
Date:	Wed, 22 Jul 2009 19:17:25 +0200
From:	Frédéric Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Li Zefan <lizf@...fujitsu.com>, hpa@...or.com,
	linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...e.hu,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:sched/core] sched: Pull up the might_sleep() check into 
	cond_resched()

2009/7/20 Peter Zijlstra <a.p.zijlstra@...llo.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.
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