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Date: Sat, 21 Jul 2007 12:02:35 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>, Ingo Molnar <mingo@elte.hu>,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH] fix theoretical ccids_{read,write}_lock() race
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On Sat, 21 Jul 2007 19:02:06 +0400 Oleg Nesterov <oleg@tv-sign.ru> wrote:

> Make sure that spin_unlock_wait() is properly ordered wrt atomic_inc().
> 
> Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
> 
> --- t/net/dccp/ccid.c~ccid	2006-12-18 18:17:31.000000000 +0300
> +++ t/net/dccp/ccid.c	2007-07-21 18:29:21.000000000 +0400
> @@ -40,6 +40,7 @@ static inline void ccids_write_unlock(vo
>  static inline void ccids_read_lock(void)
>  {
>  	atomic_inc(&ccids_lockct);
> +	smp_mb__after_atomic_inc();
>  	spin_unlock_wait(&ccids_lock);
>  }
>  

Why not just use standard rwlocks in there?

(This is probably an FAQ, but it should be).