From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751793AbdIUPeE (ORCPT ); Thu, 21 Sep 2017 11:34:04 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:42618 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751678AbdIUPeD (ORCPT ); Thu, 21 Sep 2017 11:34:03 -0400 Date: Thu, 21 Sep 2017 08:33:58 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: Steven Rostedt , Neeraj Upadhyay , josh@joshtriplett.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, linux-kernel@vger.kernel.org, sramana@codeaurora.org, prsood@codeaurora.org, pkondeti@codeaurora.org, markivx@codeaurora.org Subject: Re: Query regarding synchronize_sched_expedited and resched_cpu Reply-To: paulmck@linux.vnet.ibm.com References: <8f33e48e-ac6d-2c88-e16f-20b698c06292@codeaurora.org> <20170917010015.GW3521@linux.vnet.ibm.com> <20170918111105.15f687da@gandalf.local.home> <20170918160125.GL3521@linux.vnet.ibm.com> <20170918121213.312c82b0@gandalf.local.home> <20170918162412.GM3521@linux.vnet.ibm.com> <20170918122931.0e3341f3@gandalf.local.home> <20170918165527.GN3521@linux.vnet.ibm.com> <20170921135749.i35iq6hlxys3eb7k@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170921135749.i35iq6hlxys3eb7k@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 17092115-0044-0000-0000-000003937208 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007773; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000231; SDB=6.00920285; UDB=6.00462418; IPR=6.00700507; BA=6.00005601; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00017237; XFM=3.00000015; UTC=2017-09-21 15:34:00 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17092115-0045-0000-0000-000007C27615 Message-Id: <20170921153358.GH3521@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-09-21_02:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1707230000 definitions=main-1709210207 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 21, 2017 at 03:57:49PM +0200, Peter Zijlstra wrote: > On Mon, Sep 18, 2017 at 09:55:27AM -0700, Paul E. McKenney wrote: > > On Mon, Sep 18, 2017 at 12:29:31PM -0400, Steven Rostedt wrote: > > > On Mon, 18 Sep 2017 09:24:12 -0700 > > > "Paul E. McKenney" wrote: > > > > > > > > > > As soon as I work through the backlog of lockdep complaints that > > > > appeared in the last merge window... :-( > > > > > > > > sparse_irq_lock, I am looking at you!!! ;-) > > That one is a false positive and I have send patches to address. I did try them out, and they work fine for me when lockdep is enabled. I get build failures if lockdep is not enabled. Things are a bit crazy here, so I have not had a chance to try to fix them, though it should not be a big deal (easy for me to say!). > > > I just hit one too, and decided to write a patch to show a chain of 3 > > > when applicable. > > > > > > For example: > > > > > > Chain exists of: > > > cpu_hotplug_lock.rw_sem --> smpboot_threads_lock --> (complete)&self->parked > > > > > > Possible unsafe locking scenario by crosslock: > > > > > > CPU0 CPU1 CPU2 > > > ---- ---- ---- > > > lock(smpboot_threads_lock); > > > lock((complete)&self->parked); > > > lock(cpu_hotplug_lock.rw_sem); > > > lock(smpboot_threads_lock); > > > lock(cpu_hotplug_lock.rw_sem); > > > unlock((complete)&self->parked); > > > > > > *** DEADLOCK *** > > > > > > :-) > > > > Nice!!! > > That one looks like the watchdog thing, and Thomas was poking at that. For whatever it is worth, I am still chasing lost-timer bugs. I now know of a large number of things that are not the cause of the problem. :-/ Thanx, Paul