From patchwork Fri Apr 30 05:54:30 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrew Morton X-Patchwork-Id: 12232331 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 11EEDC43460 for ; Fri, 30 Apr 2021 05:54:35 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id B60A961459 for ; Fri, 30 Apr 2021 05:54:32 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B60A961459 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 53E6C6B0071; Fri, 30 Apr 2021 01:54:32 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 4A0166B009A; Fri, 30 Apr 2021 01:54:32 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 2F2496B009B; Fri, 30 Apr 2021 01:54:32 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0072.hostedemail.com [216.40.44.72]) by kanga.kvack.org (Postfix) with ESMTP id 0DB316B0071 for ; Fri, 30 Apr 2021 01:54:32 -0400 (EDT) Received: from smtpin29.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id C110F8249980 for ; Fri, 30 Apr 2021 05:54:31 +0000 (UTC) X-FDA: 78087968742.29.D8AD651 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf06.hostedemail.com (Postfix) with ESMTP id 09902C0007E4 for ; Fri, 30 Apr 2021 05:54:33 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id 5D726613F8; Fri, 30 Apr 2021 05:54:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1619762070; bh=XVl5cihNRZGNPdcVA4DHYqCAgU8guMhb0JYnSP8vYsY=; h=Date:From:To:Subject:In-Reply-To:From; b=yrXYS9+AEXGIYDFIGcay49RKhzbtQU+QxtjyETFO6tqNeaqtgeXbCQqNat6XpTaL3 i1k/cWQNksp6xNi5+QdsyRTRU9CgUTtyQt9oD4VXDyUUmMtGncBchtuPrFCVFM/OEF AsvhwDpyrilchcorj9uOSX+8pWEqRrjgnT2i/AL4= Date: Thu, 29 Apr 2021 22:54:30 -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 025/178] watchdog/softlockup: remove logic that tried to prevent repeated reports Message-ID: <20210430055430.nHty_v4fS%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: 09902C0007E4 Authentication-Results: imf06.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b=yrXYS9+A; dmarc=none; spf=pass (imf06.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: kjutge1zrkuc7x99frjmkrsu4nob1t1w Received-SPF: none (linux-foundation.org>: No applicable sender policy available) receiver=imf06; identity=mailfrom; envelope-from=""; helo=mail.kernel.org; client-ip=198.145.29.99 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1619762073-252647 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/softlockup: remove logic that tried to prevent repeated reports 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 --- kernel/watchdog.c | 14 ++------------ 1 file changed, 2 insertions(+), 12 deletions(-) --- a/kernel/watchdog.c~watchdog-softlockup-remove-logic-that-tried-to-prevent-repeated-reports +++ a/kernel/watchdog.c @@ -179,7 +179,6 @@ static DEFINE_PER_CPU(unsigned long, wat static DEFINE_PER_CPU(unsigned long, watchdog_report_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; @@ -411,19 +410,12 @@ static enum hrtimer_restart watchdog_tim 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. */ @@ -453,9 +445,7 @@ static enum hrtimer_restart watchdog_tim 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; }