From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755195AbbAFLFA (ORCPT ); Tue, 6 Jan 2015 06:05:00 -0500 Received: from mail-pd0-f182.google.com ([209.85.192.182]:38494 "EHLO mail-pd0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754583AbbAFLE7 (ORCPT ); Tue, 6 Jan 2015 06:04:59 -0500 Date: Tue, 6 Jan 2015 03:07:30 -0800 From: Kent Overstreet To: Peter Zijlstra Cc: Sedat Dilek , Dave Jones , Linus Torvalds , LKML , Chris Mason Subject: Re: Linux 3.19-rc3 Message-ID: <20150106110730.GA25846@kmo-pixel> References: <20150106094039.GI29390@twins.programming.kicks-ass.net> <20150106100621.GL29390@twins.programming.kicks-ass.net> <20150106110112.GQ29390@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150106110112.GQ29390@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 06, 2015 at 12:01:12PM +0100, Peter Zijlstra wrote: > On Tue, Jan 06, 2015 at 11:18:04AM +0100, Sedat Dilek wrote: > > On Tue, Jan 6, 2015 at 11:06 AM, Peter Zijlstra wrote: > > > On Tue, Jan 06, 2015 at 10:57:19AM +0100, Sedat Dilek wrote: > > >> [ 88.028739] [] aio_read_events+0x4f/0x2d0 > > >> > > > > > > Ah, that one. Chris Mason and Kent Overstreet were looking at that one. > > > I'm not touching the AIO code either ;-) > > > > I know, I was so excited when I see nearly the same output. > > > > Can you tell me why people see "similiar" problems in different areas? > > Because the debug check is new :-) It's a pattern that should not be > used but mostly works most of the times. > > > [ 181.397024] WARNING: CPU: 0 PID: 2872 at kernel/sched/core.c:7303 > > __might_sleep+0xbd/0xd0() > > [ 181.397028] do not call blocking ops when !TASK_RUNNING; state=1 > > set at [] prepare_to_wait_event+0x5d/0x110 > > > > With similiar buzzwords... namely... > > > > mutex_lock_nested > > prepare_to_wait(_event) > > __might_sleep > > > > I am asking myself... Where is the real root cause - in sched/core? > > Fix one single place VS. fix the impact at several other places? > > No, the root cause is nesting sleep primitives, this is not fixable in > the one place, both prepare_to_wait and mutex_lock are using > task_struct::state, they have to, no way around it. No, it's completely possible to construct a prepare_to_wait() that doesn't require messing with the task state. Had it for years. http://evilpiepirate.org/git/linux-bcache.git/log/?h=aio_ring_fix