From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [PATCH 3/5] writeback: fix dirtied pages accounting on sub-page
 writes
Date: Tue, 22 Nov 2011 13:57:42 +0100
Message-ID: <1321966662.5148.35.camel@twins>
References: <20111121130342.211953629@intel.com>
	 <20111121131215.905222115@intel.com> <20111122001127.GG4017@quack.suse.cz>
	 <20111122092110.GB12864@localhost> <20111122122157.GB8058@quack.suse.cz>
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Cc: Wu Fengguang <fengguang.wu@intel.com>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	Christoph Hellwig <hch@lst.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	LKML <linux-kernel@vger.kernel.org>
To: Jan Kara <jack@suse.cz>
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <20111122122157.GB8058@quack.suse.cz>
Sender: linux-kernel-owner@vger.kernel.org
List-Id: linux-fsdevel.vger.kernel.org

On Tue, 2011-11-22 at 13:21 +0100, Jan Kara wrote:
> > +             __get_cpu_var(bdp_ratelimits)++;
>   I think you need preempt_disable() and preempt_enable() pair around
> __get_cpu_var(). Otherwise a process could get rescheduled in the middle of
> read-modify-write cycle... 

there's of course the this_cpu_inc(bdp_ratelimits); thing.

On x86 that'll turn into a single insn, on others it will add the
required preempt_disable/enable bits.