Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262081AbVCHTpg (ORCPT ); Tue, 8 Mar 2005 14:45:36 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262145AbVCHTpe (ORCPT ); Tue, 8 Mar 2005 14:45:34 -0500 Received: from rproxy.gmail.com ([64.233.170.204]:57368 "EHLO rproxy.gmail.com") by vger.kernel.org with ESMTP id S262081AbVCHTcu (ORCPT ); Tue, 8 Mar 2005 14:32:50 -0500 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=beta; d=gmail.com; h=received:message-id:date:from:reply-to:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:references; b=P5efXK9d8Kc7OYpAdbTf7+UHdqHaY5AHCMdBdPDMLHKFRNhIBgkO2hhy9EoKWMXlD5jgtOLSHOEnTiozgxhENcOYbGpjogjAht0CamhSbNpAs6RpzqbbkCIEUh9kPIZr16J6Pq0BJToW+Vzl5sDPYKYmvsJ17YJ+1SfVvN+T/Jc= Message-ID: <8783be6605030811326dc8f89b@mail.gmail.com> Date: Tue, 8 Mar 2005 11:32:43 -0800 From: Ross Biro Reply-To: Ross Biro To: "Peter W. Morreale" Subject: Re: Cc: linux-kernel@vger.kernel.org In-Reply-To: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit References: Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1759 Lines: 55 On Tue, 08 Mar 2005 09:32:48 -0700, Peter W. Morreale wrote: > > This seems wrong since we've mixed locking primitives. > > Is it? It's not really wrong, it just wastes time turning interrupts off over and over again. > .... > foo() > { > unsigned long lflags; At this point, interrupts are off, the lock is held. > > spin_unlock(global_lock); Interrupts are still off, the lock is no longer held. > ... > { > spin_lock_irqsave(global_lock, &lflags); Interrupts are still off, and just to be sure we turned them off again. The lock is held. > . > . > spin_unlock_irqrestore(global_lock, &lflags); Interrupts are still off, but we restored them to the off state they were in before we grabbed the lock the last time. The lock is no longer held. > } > > spin_lock_irq(global_lock); Turn off interrupts again just to be extra sure they are off. The lock is held again. >From the looks of this code, the locking will work. But it's not what it should be. If you know foo is only called with interrupts off, then there is no reason to turn them off over and over again. Just use the standard spin_lock and spin_unlock and comment that interrupts are already off. You should also question if interrupts need to be disabled at all. If the spin lock is never grabbed at interrupt time (and probably won't be in the near future), then there is no point in turning interrupts on and off at all. Ross - 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/