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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=no 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 BAA40C3A59D for ; Mon, 19 Aug 2019 10:47:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9B1E620851 for ; Mon, 19 Aug 2019 10:47:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727367AbfHSKri (ORCPT ); Mon, 19 Aug 2019 06:47:38 -0400 Received: from mx2.suse.de ([195.135.220.15]:57640 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726477AbfHSKrh (ORCPT ); Mon, 19 Aug 2019 06:47:37 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id C51EAB643; Mon, 19 Aug 2019 10:47:36 +0000 (UTC) From: Petr Mladek To: Thomas Gleixner , Ingo Molnar , Peter Zijlstra Cc: Laurence Oberman , Vincent Whitchurch , Michal Hocko , linux-kernel@vger.kernel.org, Petr Mladek Subject: [PATCH 0/3] watchdog/softlockup: Make softlockup reports more reliable and useful Date: Mon, 19 Aug 2019 12:47:29 +0200 Message-Id: <20190819104732.20966-1-pmladek@suse.com> X-Mailer: git-send-email 2.16.4 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ( Resending this as a proper patch with updated commit messages. The original was https://lkml.kernel.org/r/20190605140954.28471-1-pmladek@suse.com ) We were analyzing logs with several softlockup reports in flush_tlb_kernel_range(). They were confusing. Especially it was not clear whether it was deadlock, livelock, or separate softlockups. It went out that even a simple busy loop: while (true) cpu_relax(); is able to produce several softlockups reports: [ 168.277520] watchdog: BUG: soft lockup - CPU#1 stuck for 22s! [cat:4865] [ 196.277604] watchdog: BUG: soft lockup - CPU#1 stuck for 22s! [cat:4865] [ 236.277522] watchdog: BUG: soft lockup - CPU#1 stuck for 23s! [cat:4865] ^^^^ This patchset fixes the problem in two steps: + 1st patch prevents restart of the watchdog from unrelated locations. Each softlockup is reported only once: [ 320.248948] watchdog: BUG: soft lockup - CPU#2 stuck for 26s! [cat:4916] + 2nd patch helps to distinguish several possible situations by regular reports. The report looks like: [ 480.372418] watchdog: BUG: soft lockup - CPU#2 stuck for 26s! [cat:4943] [ 508.372359] watchdog: BUG: soft lockup - CPU#2 stuck for 52s! [cat:4943] [ 548.372359] watchdog: BUG: soft lockup - CPU#2 stuck for 89s! [cat:4943] [ 576.372351] watchdog: BUG: soft lockup - CPU#2 stuck for 115s! [cat:4943] ^^^^^ 3rd patch provides a sample code to trigger a softlockup. Petr Mladek (3): watchdog/softlockup: Preserve original timestamp when touching watchdog externally watchdog/softlockup: Report the same softlockup regularly Test softlockup fs/proc/consoles.c | 5 ++++ fs/proc/version.c | 7 +++++ kernel/watchdog.c | 85 +++++++++++++++++++++++++++++++----------------------- 3 files changed, 61 insertions(+), 36 deletions(-) -- 2.16.4