linux-kernel - Re: [PATCH] kernel/timer.c: using spin_lock_irqsave instead of spin_lock + local_irq_save, especially when CONFIG

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Message-ID: <51C182EE.5070500@asianux.com>
Date:	Wed, 19 Jun 2013 18:07:42 +0800
From:	Chen Gang <gang.chen@...anux.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kernel/timer.c: using spin_lock_irqsave instead of spin_lock
 + local_irq_save, especially when CONFIG_LOCKDEP not defined

On 06/19/2013 05:59 PM, Thomas Gleixner wrote:
> Lockdep tracks lock ordering and the context in which a lock is
> taken. The timer base lock can be taken in interrupt context, so it
> always needs to be taken with interrupts disabled. That's what lockdep
> cares about.
> 
> And 
> 	spin_lock_irqsave(&l1, flags);
> 	spin_unlock(&l1);
> 	spin_lock(&l2);
> 	spin_unlock_irqrestore(&l2, flags);
> 
> fulfils that for both l1 and l2.
> 
> It does not matter whether the code pathes are different, what matters
> is that they are semantically the same. And that's the case.

But I feel, they are not semantically the same.

if CONFIG_LOCKDEP is not defined, spin_lock_irqsave() should call
do_raw_spin_lock_flags(), not call LOCK_CONTENDED().



Thanks.
-- 
Chen Gang

Asianux Corporation
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