linux-kernel - Re: [PATCH 1/13] BC: atomic_dec_and_lock

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Date:	Fri, 10 Nov 2006 19:46:30 +0300
From:	Kirill Korotaev <dev@...ru>
To:	Cedric Le Goater <cedric@...oater.org>
CC:	Andrew Morton <akpm@...l.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>, xemul@...nvz.org,
	devel@...nvz.org, oleg@...sign.ru, hch@...radead.org,
	matthltc@...ibm.com, ckrm-tech@...ts.sourceforge.net
Subject: Re: [PATCH 1/13] BC: atomic_dec_and_lock_irqsave() helper

> Hello Kirill, Hello Pavel,
> 
> Kirill Korotaev wrote:
> 
>>Oleg Nesterov noticed to me that the construction like
>>(used in beancounter patches and free_uid()):
>>
>>  local_irq_save(flags);
>>  if (atomic_dec_and_lock(&refcnt, &lock))
>>	  ...
>>
>>is not that good for preemtible kernels, since with preemption
>>spin_lock() can schedule() to reduce latency. However, it won't schedule
>>if interrupts are disabled.
>>
>>So this patch introduces atomic_dec_and_lock_irqsave() as a logical
>>counterpart to atomic_dec_and_lock().
> 
> 
> You should probably send that one independently from the BC 
> patchset. 
Maybe, but BCs are the only user of this so far...

Thanks,
Kirill


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