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=-3.9 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, 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 AF80AC4346E for ; Thu, 24 Sep 2020 08:45:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 618AC21D91 for ; Thu, 24 Sep 2020 08:45:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="tcXIn8tK" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727211AbgIXIpp (ORCPT ); Thu, 24 Sep 2020 04:45:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:32878 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726387AbgIXIpp (ORCPT ); Thu, 24 Sep 2020 04:45:45 -0400 Received: from mail-pf1-x441.google.com (mail-pf1-x441.google.com [IPv6:2607:f8b0:4864:20::441]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F3036C0613CE for ; Thu, 24 Sep 2020 01:45:44 -0700 (PDT) Received: by mail-pf1-x441.google.com with SMTP id z19so1466678pfn.8 for ; Thu, 24 Sep 2020 01:45:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=qcEFUagRFegtRA+c7Q/RWfZQtrVtJdKhlhnvr1c1Zzg=; b=tcXIn8tK5lvFVCLf9TZ113Haf08OtFPxoyDDXrkV37Us2tXKaGt+H+BDt8B03DjT+t Tnp+rqMxvAAgik9JI11a2Jh/r7kVtYQ/Ee7fI5tRrqNqks5aqFdnasKGLdtS13i1GN6n IzahVoDO7Qd+5KuxmQ3KWsW0fOJR+3qK+CdAIfE7wMiLCtdsKUhWZ2IBP/xGwR5RisUN 4V7h9aNOQCxrU1e1dQEpH/UzEKfouCsdVli23c09Dp5LYga6U8W+58r9drKPkHcfl7uw QOM+0iV20wJG/xCyZO4uFMFHH8tJCH19c+aS7x+YeHvQhvz3kJtnFV7yz7tlSHuOV55D Ewjw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=qcEFUagRFegtRA+c7Q/RWfZQtrVtJdKhlhnvr1c1Zzg=; b=KqAulGx3IjAxsh8BK7BIcJrugE1iL6hhEQ96+3l/yik7jWWJV7lz7fbNiEfbjiLdyg hTdbn8p3m7/jeiRZTN/VBfrWcvmhpzq116iUZavomKmOMJPLs0q47eI1UsNbdjyxe2JY HGY9XWGrT2VgxsJVuQG2CFD8NByJZpmYneV1R/nRkWLcEK3/kKwfhHRCHfzuMcXpvqtL rEyQTNHg7PgEYIsPwRxWbibVkq//51eOVFQD75/oRfLWoBg3tSqUMv9TC/mSarxNAu0s cpJyik950okzlPLKJVY/Xg3wSRnY4HwSnl0z0Z+3+z1EwKuoovi6NrjiA4ZMQ1Dfgx3s jkqA== X-Gm-Message-State: AOAM531RS3GhYH8VUwp819EeNK69iN0kyZ6zUsj70iA8Kd8vxQhT0Q0N cP4lUVOaOSN3pOGuU5DK75A= X-Google-Smtp-Source: ABdhPJwHIj2BhAHbMC1354hH6cMTwV+pRu84kxWYlo+kvN49AGuZQOFnUUBFE4A8iirLvW6Az3EKfg== X-Received: by 2002:a63:3856:: with SMTP id h22mr3055946pgn.451.1600937144394; Thu, 24 Sep 2020 01:45:44 -0700 (PDT) Received: from localhost ([2409:10:2e40:5100:6e29:95ff:fe2d:8f34]) by smtp.gmail.com with ESMTPSA id o67sm2208680pgo.8.2020.09.24.01.45.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 24 Sep 2020 01:45:43 -0700 (PDT) Date: Thu, 24 Sep 2020 17:45:41 +0900 From: Sergey Senozhatsky To: John Ogness Cc: Petr Mladek , Sergey Senozhatsky , Sergey Senozhatsky , Steven Rostedt , Linus Torvalds , Greg Kroah-Hartman , Thomas Gleixner , linux-kernel@vger.kernel.org Subject: Re: [PATCH printk 4/5] printk: remove logbuf_lock, add syslog_lock Message-ID: <20200924084541.GA541@jagdpanzerIV.localdomain> References: <20200922153816.5883-1-john.ogness@linutronix.de> <20200922153816.5883-5-john.ogness@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200922153816.5883-5-john.ogness@linutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (20/09/22 17:44), John Ogness wrote: [..] > void printk_safe_flush_on_panic(void) > { > - /* > - * Make sure that we could access the main ring buffer. > - * Do not risk a double release when more CPUs are up. > - */ > - if (raw_spin_is_locked(&logbuf_lock)) { > - if (num_online_cpus() > 1) > - return; > - > - debug_locks_off(); > - raw_spin_lock_init(&logbuf_lock); If we panic() with syslog_lock locked then we need to zap syslog_lock and disable debug_locks for kmsg_dump() to succeed. Otherwise panic() may deadlock: syslog_lock_irq() -> NMI panic() ... printk_safe_flush_on_panic(); kmsg_dump(KMSG_DUMP_PANIC); // syslog_lock_irqsave(flags) ... Did I miss the point where we make sure that kmsg_dump() will not deadlock? -ss