Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751204AbWHXMei (ORCPT ); Thu, 24 Aug 2006 08:34:38 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751205AbWHXMei (ORCPT ); Thu, 24 Aug 2006 08:34:38 -0400 Received: from elvis.mu.org ([192.203.228.196]:35806 "EHLO elvis.mu.org") by vger.kernel.org with ESMTP id S1751204AbWHXMeh (ORCPT ); Thu, 24 Aug 2006 08:34:37 -0400 Message-ID: <44ED9CB4.7070302@FreeBSD.org> Date: Thu, 24 Aug 2006 14:33:56 +0200 From: Suleiman Souhlal User-Agent: Mozilla Thunderbird 1.0.7 (X11/20051204) X-Accept-Language: en-us, en MIME-Version: 1.0 To: Andi Kleen CC: Edward Falk , linux-kernel@vger.kernel.org Subject: Re: [PATCH] Fix x86_64 _spin_lock_irqsave() References: <44ED157D.6050607@google.com> <44ED87AC.8070106@FreeBSD.org> <200608241332.40139.ak@suse.de> In-Reply-To: <200608241332.40139.ak@suse.de> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1962 Lines: 52 Andi Kleen wrote: > On Thursday 24 August 2006 13:04, Suleiman Souhlal wrote: > >>Andi Kleen wrote: >> >>>Edward Falk writes: >>> >>> >>> >>>>Add spin_lock_string_flags and _raw_spin_lock_flags() to >>>>asm-x86_64/spinlock.h so that _spin_lock_irqsave() has the same >>>>semantics on x86_64 as it does on i386 and does *not* have interrupts >>>>disabled while it is waiting for the lock. >>> >>> >>>Did it fix anything for you? >> >>I think this was to work around the fact that some buggy drivers try to >>grab spinlocks without disabling interrupts when they should, which >>would cause deadlocks when trying to rendez-vous every cpu via IPIs. > > > That doesn't help them at all because they could then deadlock later. If the driver uses spin_lock() when it knows that the hardware won't generate the interrupt that would need to be masked, and spin_lock_irqsave() elsewhere, there shouldn't be any deadlocks unless IPIs are involved. For example, say a driver uses spin_lock(&driver_lock) in its interrupt handler and spin_lock_irqsave(&driver_lock) elsewhere. Imagine CPU1 is handling a such a interrupt while CPU2 is trying to send a packet (for example). In a regular situation, CPU1 shouldn't be interrupted by anything needing driver_lock, and so it should be able to complete and let CPU2 acquire the lock. Now, if CPU3 is trying to do an IPI rendez-vous, it will interrupt CPU1 and try to interrupt CPU2 too. However, since spin_lock_irqsave() spins with interrupts disabled, the system will deadlock. With this patch, IPI rendez-vous shouldn't cause these problems, since it will let the rendez-vous will be able to complete. Or am I missing something? -- Suleiman - 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/