From mboxrd@z Thu Jan 1 00:00:00 1970 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=-19.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, 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,USER_AGENT_GIT autolearn=unavailable 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 45BCAC433B4 for ; Mon, 17 May 2021 15:00:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 260A9601FC for ; Mon, 17 May 2021 15:00:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239266AbhEQPCD (ORCPT ); Mon, 17 May 2021 11:02:03 -0400 Received: from mail.kernel.org ([198.145.29.99]:42786 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241510AbhEQOv5 (ORCPT ); Mon, 17 May 2021 10:51:57 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 3F4966146D; Mon, 17 May 2021 14:23:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1621261414; bh=N+cDqyWaNRu7Fs6ee6v1kiQ73FqSCuRxLtsnmHdnzyU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=00VVG1peHKV8JWJf/iCa/Fo9AWxJnvhr8x5MZjQJS0HCGTKoGbEiDuq67l6P7eZOs H9i4j2mTst+4Jw0LXPjQw4Y8cTN4xN3MTXBRzV57qD7gtAKuCdWZqcXH/B1dTqbcBd isppNmK8x24p678cqY2rujczyfIQO8XfgplXQBAA= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Petr Mladek , "Peter Zijlstra (Intel)" , Ingo Molnar , Laurence Oberman , Michal Hocko , Thomas Gleixner , Vincent Whitchurch , Andrew Morton , Linus Torvalds , Sasha Levin Subject: [PATCH 5.11 111/329] watchdog: fix barriers when printing backtraces from all CPUs Date: Mon, 17 May 2021 16:00:22 +0200 Message-Id: <20210517140305.866570203@linuxfoundation.org> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210517140302.043055203@linuxfoundation.org> References: <20210517140302.043055203@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Petr Mladek [ Upstream commit 9f113bf760ca90d709f8f89a733d10abb1f04a83 ] 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 Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- kernel/watchdog.c | 17 ++++++----------- 1 file changed, 6 insertions(+), 11 deletions(-) diff --git a/kernel/watchdog.c b/kernel/watchdog.c index 122e272ad7f2..01bf977090dc 100644 --- a/kernel/watchdog.c +++ b/kernel/watchdog.c @@ -393,11 +393,12 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) 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; } @@ -415,14 +416,8 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) 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); -- 2.30.2