From patchwork Fri Apr 30 05:54:33 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrew Morton X-Patchwork-Id: 12232333 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id F3E00C433ED for ; Fri, 30 Apr 2021 05:54:37 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id A326D61459 for ; Fri, 30 Apr 2021 05:54:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A326D61459 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 4524C6B0072; Fri, 30 Apr 2021 01:54:35 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 40E826B009B; Fri, 30 Apr 2021 01:54:35 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 27B466B009C; Fri, 30 Apr 2021 01:54:35 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0066.hostedemail.com [216.40.44.66]) by kanga.kvack.org (Postfix) with ESMTP id 07BDC6B0072 for ; Fri, 30 Apr 2021 01:54:35 -0400 (EDT) Received: from smtpin36.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id C18D58249980 for ; Fri, 30 Apr 2021 05:54:34 +0000 (UTC) X-FDA: 78087968868.36.4DE71AC Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf09.hostedemail.com (Postfix) with ESMTP id DCAA8600010F for ; Fri, 30 Apr 2021 05:54:26 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id 6C8E961424; Fri, 30 Apr 2021 05:54:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1619762073; bh=qfTMhIWEwW56emfGXAIdIJTYEEzRXeA872mIJ/2ddKg=; h=Date:From:To:Subject:In-Reply-To:From; b=hOx+13+RZsj8arvOHp7BaFOFB14RnRzY5/qX64QuAZPGPcfjpygo/wEgzmjiX51Lg 7FzMjptd96RO4vAc/uytxxjoQm6ZdaRnK/e5fkghBTp6QYiz7A0sBIz+QgCKgEyinX 3FwjQSNOrkkznfP157ioZ+WBVQV8SUvz/TO/b/HI= Date: Thu, 29 Apr 2021 22:54:33 -0700 From: Andrew Morton To: akpm@linux-foundation.org, linux-mm@kvack.org, loberman@redhat.com, mhocko@suse.com, mingo@kernel.org, mm-commits@vger.kernel.org, peterz@infradead.org, pmladek@suse.com, tglx@linutronix.de, torvalds@linux-foundation.org, vincent.whitchurch@axis.com Subject: [patch 026/178] watchdog: fix barriers when printing backtraces from all CPUs Message-ID: <20210430055433.mPeQY0F3d%akpm@linux-foundation.org> In-Reply-To: <20210429225251.02b6386d21b69255b4f6c163@linux-foundation.org> User-Agent: s-nail v14.8.16 X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: DCAA8600010F Authentication-Results: imf09.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b=hOx+13+R; dmarc=none; spf=pass (imf09.hostedemail.com: domain of akpm@linux-foundation.org designates 198.145.29.99 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org X-Stat-Signature: x6kj9szf8imjrqt4e4tno96f5en9zyfy Received-SPF: none (linux-foundation.org>: No applicable sender policy available) receiver=imf09; identity=mailfrom; envelope-from=""; helo=mail.kernel.org; client-ip=198.145.29.99 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1619762066-524157 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: From: Petr Mladek Subject: watchdog: fix barriers when printing backtraces from all CPUs Any parallel softlockup reports are skipped when one CPU is already printing backtraces from all CPUs. The exclusive rights are synchronized using one bit in soft_lockup_nmi_warn. There is also one memory barrier that does not make much sense. Use two barriers on the right location to prevent mixing two reports. [pmladek@suse.com: use bit lock operations to prevent multiple soft-lockup reports] Link: https://lkml.kernel.org/r/YFSVsLGVWMXTvlbk@alley Link: https://lkml.kernel.org/r/20210311122130.6788-6-pmladek@suse.com Signed-off-by: Petr Mladek Acked-by: Peter Zijlstra (Intel) Cc: Ingo Molnar Cc: Laurence Oberman Cc: Michal Hocko Cc: Thomas Gleixner Cc: Vincent Whitchurch Signed-off-by: Andrew Morton --- kernel/watchdog.c | 17 ++++++----------- 1 file changed, 6 insertions(+), 11 deletions(-) --- a/kernel/watchdog.c~watchdog-fix-barriers-when-printing-backtraces-from-all-cpus +++ a/kernel/watchdog.c @@ -410,11 +410,12 @@ static enum hrtimer_restart watchdog_tim if (kvm_check_and_clear_guest_paused()) return HRTIMER_RESTART; + /* + * Prevent multiple soft-lockup reports if one cpu is already + * engaged in dumping all cpu back traces. + */ if (softlockup_all_cpu_backtrace) { - /* Prevent multiple soft-lockup reports if one cpu is already - * engaged in dumping cpu back traces - */ - if (test_and_set_bit(0, &soft_lockup_nmi_warn)) + if (test_and_set_bit_lock(0, &soft_lockup_nmi_warn)) return HRTIMER_RESTART; } @@ -432,14 +433,8 @@ static enum hrtimer_restart watchdog_tim dump_stack(); if (softlockup_all_cpu_backtrace) { - /* Avoid generating two back traces for current - * given that one is already made above - */ trigger_allbutself_cpu_backtrace(); - - clear_bit(0, &soft_lockup_nmi_warn); - /* Barrier to sync with other cpus */ - smp_mb__after_atomic(); + clear_bit_unlock(0, &soft_lockup_nmi_warn); } add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK);