From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751340Ab3CSL35 (ORCPT ); Tue, 19 Mar 2013 07:29:57 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:23176 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750750Ab3CSL34 (ORCPT ); Tue, 19 Mar 2013 07:29:56 -0400 X-Authority-Analysis: v=2.0 cv=UN5f7Vjy c=1 sm=0 a=rXTBtCOcEpjy1lPqhTCpEQ==:17 a=mNMOxpOpBa8A:10 a=bGeQnFoGQusA:10 a=5SG0PmZfjMsA:10 a=IkcTkHD0fZMA:10 a=meVymXHHAAAA:8 a=mxv2HPhRFNcA:10 a=frLJNqDbYEwVCny_utsA:9 a=QEXdDO2ut3YA:10 a=rXTBtCOcEpjy1lPqhTCpEQ==:117 X-Cloudmark-Score: 0 X-Authenticated-User: X-Originating-IP: 74.67.115.198 Message-ID: <1363692594.5938.14.camel@gandalf.local.home> Subject: Re: [PATCH] scheduler: convert BUG_ON()s in try_to_wake_up_local() to WARN_ON_ONCE()s From: Steven Rostedt To: Peter Zijlstra Cc: Tejun Heo , Ingo Molnar , linux-kernel@vger.kernel.org Date: Tue, 19 Mar 2013 07:29:54 -0400 In-Reply-To: <1363688074.22553.14.camel@laptop> References: <20130318192234.GD3042@htj.dyndns.org> <1363688074.22553.14.camel@laptop> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.4.4-2 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2013-03-19 at 11:14 +0100, Peter Zijlstra wrote: > On Mon, 2013-03-18 at 12:22 -0700, Tejun Heo wrote: > > try_to_wake_up_local() should only be invoked to wake up another task > > in the same runqueue and BUG_ON()s are used to enforce the rule. > > Missing try_to_wake_up_local() can stall workqueue execution but such > > stalls are likely to be finite either by another work item being > > queued or the one blocked getting unblocked. There's no reason to > > trigger BUG while holding rq lock crashing the whole system. > > > > Convert BUG_ON()s in try_to_wake_up_local() to WARN_ON_ONCE()s. > > Doesn't really matter either way, the printk()s triggered by either > will very likely kill the system anyhow ;-) Only if something blocks on the console lock, and it tries to wake it up. But even then, it has to be a reverse rq locking order, or wakeup on the same rq that its running on (which is very unlikely). I admit that it doesn't "solve" the bug. But at least there's a chance to investigate what happened when the bug does occur. Right now we have only one conclusion when the bug triggers, and that's a hard lockup. -- Steve