From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752857AbYIBOpb (ORCPT ); Tue, 2 Sep 2008 10:45:31 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751437AbYIBOpX (ORCPT ); Tue, 2 Sep 2008 10:45:23 -0400 Received: from casper.infradead.org ([85.118.1.10]:39165 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751325AbYIBOpW (ORCPT ); Tue, 2 Sep 2008 10:45:22 -0400 Subject: Re: [PATCH] [2/2] Don't complain about disabled irqs when the system has paniced From: Peter Zijlstra To: Andi Kleen Cc: torvalds@osdl.org, linux-kernel , Jens Axboe , Nick Piggin In-Reply-To: <20080902144051.GM18288@one.firstfloor.org> References: <20080902349.573187695@firstfloor.org> <20080902134923.9A7EF3E6A01@basil.firstfloor.org> <1220365683.8609.58.camel@twins> <20080902144051.GM18288@one.firstfloor.org> Content-Type: text/plain Date: Tue, 02 Sep 2008 16:45:17 +0200 Message-Id: <1220366717.8609.65.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.22.3.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2008-09-02 at 16:40 +0200, Andi Kleen wrote: > On Tue, Sep 02, 2008 at 04:28:03PM +0200, Peter Zijlstra wrote: > > On Tue, 2008-09-02 at 15:49 +0200, Andi Kleen wrote: > > > panic calls smp_send_stop which eventually calls smp_call_function_*. > > > smp_call_function warns about disabled interrupts. But it's legal > > > to call panic in this case. When this happens panic() prints > > > several ugly backtraces. So don't check for disabled interrupts > > > in panic state. > > > > While it might be legal for panic to be called from such contexts, I > > understand those warnings are there to warn of deadlocks. > > > > So with the below patch you allow panic to deadlock if I understand > > things correctly. > > Please describe the deadlock exactly. I don't think it can deadlock > in this case. Then why are those warnings there? The deadlock is for the CSD_FLAG_WAIT case, which can always happen due to the static csd data fallback. The deadlock scenario is long the lines of two such smp_call_function*() both under irq disabled calling each other with CSD_FLAG_WAIT set. Neither remote cpu will handle the IPI due to irqs being disabled, so we'll wait at-infinitum for completion. > Besides do you prefer to not allow panic from interrupts/machine > checks etc. anymore? However did I imply that, I just said your fix looked iffy.