Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756423AbXK1Exh (ORCPT ); Tue, 27 Nov 2007 23:53:37 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753999AbXK1Ex1 (ORCPT ); Tue, 27 Nov 2007 23:53:27 -0500 Received: from idcmail-mo1so.shaw.ca ([24.71.223.10]:62109 "EHLO pd3mo3so.prod.shaw.ca" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753972AbXK1Ex0 (ORCPT ); Tue, 27 Nov 2007 23:53:26 -0500 Date: Tue, 27 Nov 2007 22:53:20 -0600 From: Robert Hancock Subject: Re: Question regarding mutex locking In-reply-to: To: Larry Finger Cc: LKML Message-id: <474CF440.2000001@shaw.ca> MIME-version: 1.0 Content-type: text/plain; charset=ISO-8859-1; format=flowed Content-transfer-encoding: 7bit References: User-Agent: Thunderbird 2.0.0.9 (Windows/20071031) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 885 Lines: 26 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() > > .. > > if (hold_lock) > mutex_unlock() Not if another task could be acquiring that lock at the same time, which is probably the case, otherwise you wouldn't need the mutex. In other words, if you're going to do this, you might as well toss the mutex entirely as it's about the same effect.. -- Robert Hancock Saskatoon, SK, Canada To email, remove "nospam" from hancockr@nospamshaw.ca Home Page: http://www.roberthancock.com/ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/