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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 F1E0AC433E0 for ; Mon, 29 Mar 2021 11:22:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BCFC061938 for ; Mon, 29 Mar 2021 11:22:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232347AbhC2LWT (ORCPT ); Mon, 29 Mar 2021 07:22:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60788 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232206AbhC2LVp (ORCPT ); Mon, 29 Mar 2021 07:21:45 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DAD49C061574 for ; Mon, 29 Mar 2021 04:21:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=rtyz5hktwyQm5GdRX1cmqiUToMOy31fqUOx4emPDbTA=; b=HU7UJYrf+JnrazLZO+MCNanPjC BupyrV9OwMSCYJ2NiqPIzZdp3cQFYOmIccn+aa2A0ur3NIXXFIg1vBWZX8GSo+Jp/yLFQnCCU2df4 hV6v/qZ+YxZli8EsFvXy4sOJFWqFGzDkjQ6s1WhHkCDXD90AiE/JwJPSR7EOlhm4S2CeIdwkULQCK YmHfHreQULkrbp5w8FHXauehgehRmV2AQVPRjRNG9pDZ2trA816rPBzVcslqVrfVLHGfEGFcPXS2z QSMkqSEBiWXEEYoZBD+jx+NAtQlv8BCFv9vjbVOr4PhyWvT+N03BD88X1Ijkw29qiVClgD7S0HShp rNdGMJsw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94 #2 (Red Hat Linux)) id 1lQpvK-001Seu-PA; Mon, 29 Mar 2021 11:19:28 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id C2235304B90; Mon, 29 Mar 2021 13:19:07 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 8DE19207539C2; Mon, 29 Mar 2021 13:19:07 +0200 (CEST) Date: Mon, 29 Mar 2021 13:19:07 +0200 From: Peter Zijlstra To: Daniel Thompson Cc: Waiman Long , Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Bharata B Rao , Phil Auld , linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] sched/debug: Don't disable IRQ when acquiring sched_debug_lock Message-ID: References: <20210327232529.2349-1-longman@redhat.com> <20210329102345.6awrhtlrueqwhrpi@maple.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210329102345.6awrhtlrueqwhrpi@maple.lan> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 29, 2021 at 11:23:45AM +0100, Daniel Thompson wrote: > On Sat, Mar 27, 2021 at 07:25:28PM -0400, Waiman Long wrote: > > The sched_debug_lock was used only in print_cpu(). The > > print_cpu() function has two callers - sched_debug_show() and > > sysrq_sched_debug_show(). Both of them are invoked by user action > > (sched_debug file and sysrq-t). As print_cpu() won't be called from > > interrupt context at all, there is no point in disabling IRQ when > > acquiring sched_debug_lock. > > This looks like it introduces a deadlock risk if sysrq-t triggers from an > interrupt context. Has the behaviour of sysrq changed recently or will > tools like MAGIC_SYSRQ_SERIAL still trigger from interrupt context? Yeah, sysrq-t is very often interrupt context. The patch is clearly bogus.