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=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 E3E1AC55ABD for ; Thu, 12 Nov 2020 10:50:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8FF7E22227 for ; Thu, 12 Nov 2020 10:50:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728112AbgKLKud convert rfc822-to-8bit (ORCPT ); Thu, 12 Nov 2020 05:50:33 -0500 Received: from eu-smtp-delivery-151.mimecast.com ([185.58.86.151]:31780 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727982AbgKLKu3 (ORCPT ); Thu, 12 Nov 2020 05:50:29 -0500 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-233-NtPqp2y3NwaRSrBCxNKq9Q-1; Thu, 12 Nov 2020 10:50:24 +0000 X-MC-Unique: NtPqp2y3NwaRSrBCxNKq9Q-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Thu, 12 Nov 2020 10:50:24 +0000 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Thu, 12 Nov 2020 10:50:24 +0000 From: David Laight To: "linux-kernel@vger.kernel.org" , "Peter Zijlstra" Subject: Repeated 'watchdog soft lockup' messages Thread-Topic: Repeated 'watchdog soft lockup' messages Thread-Index: Ada434PEoNfBdUnWS36emNJ9dr0htA== Date: Thu, 12 Nov 2020 10:50:24 +0000 Message-ID: <4e624f005f3744eb82adfa1e5ef0d683@AcuMS.aculab.com> Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Due to a coding fubar (in my own driver) I managed to sleep a process that held a spinlock. Unluckily all 8 cpus ended up trying to acquire the spinlock before the process woke. As might be expected the system froze. I'd got a serial console connected so could see the kernel messages. It was almost continuously generating output saying that each cpu was 'stuck for 22s!' (sometimes 23s). What I don't understand is what was resetting the watchdog so that I got multiple messages for each cpu at intervals of (typically) 28 seconds. The watchdog code seems to only output the trace once. But that clearly wasn't working. Any idea why? kernel is 5.9.0 David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)