Message-ID: <474F63A5.2000907@serpentine.com>
Date: Thu, 29 Nov 2007 17:13:09 -0800
From: "Bryan O'Sullivan" <bos@serpentine.com>
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To: Larry Finger <Larry.Finger@lwfinger.net>
CC: LKML <linux-kernel@vger.kernel.org>
Subject: Re: Question regarding mutex locking
References: <474CF06C.8020208@lwfinger.net>
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Larry Finger wrote:
> If a particular routine needs to lock a mutex, but it may be entered with that mutex already locked,
> would the following code be SMP safe?
> 
> hold_lock = mutex_trylock()

The common way to deal with this is first to restructure your function 
into two.  One always acquires the lock, and the other (often written 
with a "__" prefix) never acquires it.  The never-acquire code does the 
actual work, and the always-acquire function calls it.

You then refactor the callers so that you don't have any code paths on 
which you can't predict whether or not the lock will be held.

	<b
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