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x-return-mx=pass smtp.domain=vger.kernel.org smtp.result=pass smtp_org.domain=kernel.org smtp_org.result=pass smtp_is_org_domain=no header.domain=gmail.com header.result=pass header_is_org_domain=yes Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750740AbeBCF6g (ORCPT ); Sat, 3 Feb 2018 00:58:36 -0500 Received: from mail-pl0-f67.google.com ([209.85.160.67]:34156 "EHLO mail-pl0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750716AbeBCF6f (ORCPT ); Sat, 3 Feb 2018 00:58:35 -0500 X-Google-Smtp-Source: AH8x226Zxe/FtAqRCaDTY/l+0morrVt6Db4VgVQsH2Jk10LVJ/YKYJ8L4t1FXCZch0YhmnLA+3R/CQ== Date: Sat, 3 Feb 2018 15:58:22 +1000 From: Nicholas Piggin To: Michael Ellerman Cc: alexander.levin@verizon.com, "linux-kernel\@vger.kernel.org" , "stable\@vger.kernel.org" Subject: Re: [PATCH AUTOSEL for 3.18 36/40] powerpc/xmon: Avoid tripping SMP hardlockup watchdog Message-ID: <20180203155822.01e2e34b@roar.ozlabs.ibm.com> In-Reply-To: <87h8r47yl1.fsf@concordia.ellerman.id.au> References: <20171213015905.7059-1-alexander.levin@verizon.com> <20171213015905.7059-36-alexander.levin@verizon.com> <87lgi6ai40.fsf@concordia.ellerman.id.au> <20171213134453.4sbmin2tjprrjnty@sasha-lappy> <87h8r47yl1.fsf@concordia.ellerman.id.au> Organization: IBM X-Mailer: Claws Mail 3.16.0 (GTK+ 2.24.31; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Tue, 30 Jan 2018 15:35:54 +1100 Michael Ellerman wrote: > alexander.levin@verizon.com writes: > > > On Thu, Dec 14, 2017 at 12:10:39AM +1100, Michael Ellerman wrote: > >>alexander.levin@verizon.com writes: > >> > >>> From: Nicholas Piggin > >>> > >>> [ Upstream commit 064996d62a33ffe10264b5af5dca92d54f60f806 ] > >>> > >>> The SMP hardlockup watchdog cross-checks other CPUs for lockups, which > >>> causes xmon headaches because it's assuming interrupts hard disabled > >>> means no watchdog troubles. Try to improve that by calling > >>> touch_nmi_watchdog() in obvious places where secondaries are spinning. > >>> > >>> Also annotate these spin loops with spin_begin/end calls. > >> > >>These macros didn't exist until 4.13, and haven't been backported AFAIK. > > > > But the touch_nmi_watchdog() bits are something we want in stable, right? > > I don't think you need them unless you've also back ported > arch/powerpc/kernel/watchdog.c, which I don't think you have. > > Maybe Nick can confirm? I'm not 100% sure. The CPUs only check themselves for lockups. They will blow their threshold when in xmon, but when they come out of xmon, I think by a quirk of our local_irq_enable() implementation that actually checks timers explicitly and runs them first before re-enabling hard interrupts, then our heartbeat starts up again just before the perf interrupt would come in to report the lockup. I think. Given that we've had no reports of misbehaviour of the old perf watchdog, I would say you can skip the backport. Thanks, Nick