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=-19.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 F1A4EC43462 for ; Wed, 5 May 2021 17:05:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C55C4613C0 for ; Wed, 5 May 2021 17:05:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237672AbhEEREM (ORCPT ); Wed, 5 May 2021 13:04:12 -0400 Received: from mail.kernel.org ([198.145.29.99]:44942 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234046AbhEEQzl (ORCPT ); Wed, 5 May 2021 12:55:41 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 373AF61462; Wed, 5 May 2021 16:38:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1620232733; bh=xtG7WbmAe5GyHpRvMmugAktrglxWiM55d6rGpGh9mqI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=uPQqwg43OhSuqviUOteLPDrJtGF9gO8EQsPJumzE98ZvgzOB2NAQQvWVeoj9u+t9X WUxikBxq0aoYRAcgsYhG96um6z1QmusDY73cSnmLStANl7XkkauNHSdcIHRCq5aMSw Zq6mn5SAXlsDQ3M0cHx5f36poK8PuhanvcxCnBFJmkXgLSRBWTMahPNgy+XqE+WmKK w4U/5v7w/ss7JjrpawiR0u1aQ17OG9Tgii3R68caovOeH4SLIr4BJUfggj6/iVo2ZP r8LBS55OJE2nKiEITYFYxHJUqjq19gH1AV6xDSlD85eDae0vKP4aQY/Pz5qnFuXshJ Yz1voedPOdb8g== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Petr Mladek , Ingo Molnar , Laurence Oberman , Michal Hocko , Peter Zijlstra , Thomas Gleixner , Vincent Whitchurch , Andrew Morton , Linus Torvalds , Sasha Levin Subject: [PATCH AUTOSEL 5.10 84/85] watchdog/softlockup: remove logic that tried to prevent repeated reports Date: Wed, 5 May 2021 12:36:47 -0400 Message-Id: <20210505163648.3462507-84-sashal@kernel.org> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20210505163648.3462507-1-sashal@kernel.org> References: <20210505163648.3462507-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Petr Mladek [ Upstream commit 1bc503cb4a2638fb1c57801a7796aca57845ce63 ] The softlockup detector does some gymnastic with the variable soft_watchdog_warn. It was added by the commit 58687acba59266735ad ("lockup_detector: Combine nmi_watchdog and softlockup detector"). The purpose is not completely clear. There are the following clues. They describe the situation how it looked after the above mentioned commit: 1. The variable was checked with a comment "only warn once". 2. The variable was set when softlockup was reported. It was cleared only when the CPU was not longer in the softlockup state. 3. watchdog_touch_ts was not explicitly updated when the softlockup was reported. Without this variable, the report would normally be printed again during every following watchdog_timer_fn() invocation. The logic has got even more tangled up by the commit ed235875e2ca98 ("kernel/watchdog.c: print traces for all cpus on lockup detection"). After this commit, soft_watchdog_warn is set only when softlockup_all_cpu_backtrace is enabled. But multiple reports from all CPUs are prevented by a new variable soft_lockup_nmi_warn. Conclusion: The variable probably never worked as intended. In each case, it has not worked last many years because the softlockup was reported repeatedly after the full period defined by watchdog_thresh. The reason is that watchdog gets touched in many known slow paths, for example, in printk_stack_address(). This code is called also when printing the softlockup report. It means that the watchdog timestamp gets updated after each report. Solution: Simply remove the logic. People want the periodic report anyway. Link: https://lkml.kernel.org/r/20210311122130.6788-5-pmladek@suse.com Signed-off-by: Petr Mladek Cc: Ingo Molnar Cc: Laurence Oberman Cc: Michal Hocko Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Vincent Whitchurch Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- kernel/watchdog.c | 14 ++------------ 1 file changed, 2 insertions(+), 12 deletions(-) diff --git a/kernel/watchdog.c b/kernel/watchdog.c index 7776d53a015c..122e272ad7f2 100644 --- a/kernel/watchdog.c +++ b/kernel/watchdog.c @@ -172,7 +172,6 @@ static u64 __read_mostly sample_period; static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts); static DEFINE_PER_CPU(struct hrtimer, watchdog_hrtimer); static DEFINE_PER_CPU(bool, softlockup_touch_sync); -static DEFINE_PER_CPU(bool, soft_watchdog_warn); static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts); static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved); static unsigned long soft_lockup_nmi_warn; @@ -394,19 +393,12 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) if (kvm_check_and_clear_guest_paused()) return HRTIMER_RESTART; - /* only warn once */ - if (__this_cpu_read(soft_watchdog_warn) == true) - return HRTIMER_RESTART; - 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)) { - /* Someone else will report us. Let's give up */ - __this_cpu_write(soft_watchdog_warn, true); + if (test_and_set_bit(0, &soft_lockup_nmi_warn)) return HRTIMER_RESTART; - } } /* Start period for the next softlockup warning. */ @@ -436,9 +428,7 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK); if (softlockup_panic) panic("softlockup: hung tasks"); - __this_cpu_write(soft_watchdog_warn, true); - } else - __this_cpu_write(soft_watchdog_warn, false); + } return HRTIMER_RESTART; } -- 2.30.2