Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752241AbZAZPWe (ORCPT ); Mon, 26 Jan 2009 10:22:34 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751328AbZAZPW0 (ORCPT ); Mon, 26 Jan 2009 10:22:26 -0500 Received: from mx3.mail.elte.hu ([157.181.1.138]:40953 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751212AbZAZPWZ (ORCPT ); Mon, 26 Jan 2009 10:22:25 -0500 Date: Mon, 26 Jan 2009 16:22:13 +0100 From: Ingo Molnar To: Alexey Zaytsev Cc: Nick Piggin , Peter Zijlstra , Laurent Riffard , Kernel development list Subject: [PATCH] sched: improve preempt debugging Message-ID: <20090126152213.GI9128@elte.hu> References: <0090126150909.GG9128@elte.hu> <20090126151521.8534.46503.stgit@nx> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090126151521.8534.46503.stgit@nx> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2561 Lines: 78 * Alexey Zaytsev wrote: > From: Alexey Zaytsev > Subject: [PATCH] Set the initial softirq preempt count to SOFTIRQ_OFFSET > > Does not changes the preemption semantics, as the > softirq's obviously can't be preempted, but fixes > a spurious warning in sub_preempt_count, which > happens when the preempt count is returned to > zero, and the interrupted thread is holding the > BKL. > > Signed-off-by: Alexey Zaytsev applied to tip/sched/urgent, thanks Alexey. I also re-added Nick's original patch on top of that (see it below) - this way we'll see whether it's all sorted out for good. Thanks, Ingo ------------------> >From ed094285f3495ad5393fc424011c926f1b6138c1 Mon Sep 17 00:00:00 2001 From: Nick Piggin Date: Tue, 30 Sep 2008 20:50:27 +1000 Subject: [PATCH] sched: improve preempt debugging This patch helped me out with a problem I recently had.... Basically, when the kernel lock is held, then preempt_count underflow does not get detected until it is released which may be a long time (and arbitrarily, eg at different points it may be rescheduled). If the bkl is released at schedule, the resulting output is actually fairly cryptic... With any other lock that elevates preempt_count, it is illegal to schedule under it (which would get found pretty quickly). bkl allows scheduling with preempt_count elevated, which makes underflows hard to debug. Signed-off-by: Ingo Molnar [ This is a re-try of this commit: 7317d7b: sched: improve preempt debugging which was reverted in: 01e3eb8: Revert "sched: improve preempt debugging" because this commit: d04d99d: x86: set the initial softirq preempt count to SOFTIRQ_OFFSET Fixes the real cause of the spurious warning. ] --- kernel/sched.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/kernel/sched.c b/kernel/sched.c index 52bbf1c..8c2be1e 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -4440,7 +4440,7 @@ void __kprobes sub_preempt_count(int val) /* * Underflow? */ - if (DEBUG_LOCKS_WARN_ON(val > preempt_count())) + if (DEBUG_LOCKS_WARN_ON(val > preempt_count() - (!!kernel_locked()))) return; /* * Is the spinlock portion underflowing? -- 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/