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=-16.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 DB87AC433E0 for ; Sat, 6 Feb 2021 05:42:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A054964FCB for ; Sat, 6 Feb 2021 05:42:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229544AbhBFFmU (ORCPT ); Sat, 6 Feb 2021 00:42:20 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49834 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229466AbhBFFmN (ORCPT ); Sat, 6 Feb 2021 00:42:13 -0500 Received: from mail-pj1-x1035.google.com (mail-pj1-x1035.google.com [IPv6:2607:f8b0:4864:20::1035]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1F9D7C06174A for ; Fri, 5 Feb 2021 21:41:33 -0800 (PST) Received: by mail-pj1-x1035.google.com with SMTP id l18so5002612pji.3 for ; Fri, 05 Feb 2021 21:41:33 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance-com.20150623.gappssmtp.com; s=20150623; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=bNFuERZtgElUwSwPcuopIAKfEJzr5N/WLsw0DMTHunA=; b=rJn/klKUTijUmoLIlHkDH59l/AeupUiiCYyaoxM29m+Mfg/xIoydcVDCfHZ7aS46OX ypPqFXcxQLNhhgka3TV91FynhqtLG50qH/w+aABe1iY/epLI5p3Qn0oGdPq1WZD8O+AB eVeud68s4ATuQbzHTDSe8EiSGigna8SIlQnAQwHLQHJayRdE1qzpAUpW9hqJyxbVklyP gLT1xoVouC8moi624zTLKgq0DildevJzWBJsnDvH8JQNEd+OwBvy7ISyzp72bPMW3OgK jPuCB5MHTZPtFKvLwoMOWLJmhv06z5xftH+2hkx7Ah8dQUCdb9rwb4GnPiIL78JW4A5U 32vg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=bNFuERZtgElUwSwPcuopIAKfEJzr5N/WLsw0DMTHunA=; b=RGEt6zBLjK5/IJz1V9ErMNQ61vrNxmVGnVVNpr6D8QQCbDQndvHJ1syRnmZhCDPYnA +q5tPTAqgn4YHbhAziif9uo45GFZULoXWygkcCykqS2zN+m29fporhYke5RUe02bn5dj QttjwQ9rjPyrau+LxgPEWfPDc3i2hBGgwPuL9x4PAl1d3scHExmjADgd/f/NNeyGL5K/ XvcDP5l/zhpChGZYZ+BqmGOWhzGgcG2Hvj1xvecYwLJSpIDfcqRFuNs3EpgT4PF1Gdzm 2wDJZEjyWU9VbeRUUMb8TjFKiwKrHUSlocV/+QzBjMtkkRpxbB/VT++Ru80vSdq0efMt zKcg== X-Gm-Message-State: AOAM533iLUbqCy+SeLROG4jQ/Ql6AHTGIYjVsumlWkU0H6kNzcN4AInh inp3DdwKqa2D4nn9cl9eomYzZQ== X-Google-Smtp-Source: ABdhPJwbke4hHmUaHQwAs84+fOqYCB1yJJMpcOBDUIRk/hEKkVPmw7DWZu1U+WVd6BACBW8A/FVzeQ== X-Received: by 2002:a17:90a:4148:: with SMTP id m8mr7278642pjg.184.1612590092638; Fri, 05 Feb 2021 21:41:32 -0800 (PST) Received: from localhost.bytedance.net ([139.177.225.239]) by smtp.gmail.com with ESMTPSA id x17sm11500816pff.180.2021.02.05.21.41.29 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Fri, 05 Feb 2021 21:41:32 -0800 (PST) From: Muchun Song To: pmladek@suse.com, sergey.senozhatsky@gmail.com, rostedt@goodmis.org, john.ogness@linutronix.de, akpm@linux-foundation.org Cc: linux-kernel@vger.kernel.org, Muchun Song Subject: [PATCH v2] printk: fix deadlock when kernel panic Date: Sat, 6 Feb 2021 13:41:24 +0800 Message-Id: <20210206054124.6743-1-songmuchun@bytedance.com> X-Mailer: git-send-email 2.21.0 (Apple Git-122) MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org We found a deadlock bug on our server when the kernel panic. It can be described in the following diagram. CPU0: CPU1: panic rcu_dump_cpu_stacks kdump_nmi_shootdown_cpus nmi_trigger_cpumask_backtrace register_nmi_handler(crash_nmi_callback) printk_safe_flush __printk_safe_flush raw_spin_lock_irqsave(&read_lock) // send NMI to other processors apic_send_IPI_allbutself(NMI_VECTOR) // NMI interrupt, dead loop crash_nmi_callback printk_safe_flush_on_panic printk_safe_flush __printk_safe_flush // deadlock raw_spin_lock_irqsave(&read_lock) The register_nmi_handler() can be called in the __crash_kexec() or the crash_smp_send_stop() on the x86-64. Because CPU1 is interrupted by the NMI with holding the read_lock and crash_nmi_callback() never returns, CPU0 can deadlock when printk_safe_flush_on_panic() is called. When we hold the read_lock and then interrupted by the NMI, if the NMI handler call nmi_panic(), it is also can lead to deadlock. In order to fix it, we make read_lock global and rename it to safe_read_lock. And we handle safe_read_lock the same way in printk_safe_flush_on_panic() as we handle logbuf_lock there. Fixes: cf9b1106c81c ("printk/nmi: flush NMI messages on the system panic") Signed-off-by: Muchun Song --- v2: - handle read_lock the same way as we handle logbuf_lock there. Thanks Petr. kernel/printk/printk_safe.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c index a0e6f746de6c..2e9e3ed7d63e 100644 --- a/kernel/printk/printk_safe.c +++ b/kernel/printk/printk_safe.c @@ -45,6 +45,8 @@ struct printk_safe_seq_buf { static DEFINE_PER_CPU(struct printk_safe_seq_buf, safe_print_seq); static DEFINE_PER_CPU(int, printk_context); +static DEFINE_RAW_SPINLOCK(safe_read_lock); + #ifdef CONFIG_PRINTK_NMI static DEFINE_PER_CPU(struct printk_safe_seq_buf, nmi_print_seq); #endif @@ -180,8 +182,6 @@ static void report_message_lost(struct printk_safe_seq_buf *s) */ static void __printk_safe_flush(struct irq_work *work) { - static raw_spinlock_t read_lock = - __RAW_SPIN_LOCK_INITIALIZER(read_lock); struct printk_safe_seq_buf *s = container_of(work, struct printk_safe_seq_buf, work); unsigned long flags; @@ -195,7 +195,7 @@ static void __printk_safe_flush(struct irq_work *work) * different CPUs. This is especially important when printing * a backtrace. */ - raw_spin_lock_irqsave(&read_lock, flags); + raw_spin_lock_irqsave(&safe_read_lock, flags); i = 0; more: @@ -232,7 +232,7 @@ static void __printk_safe_flush(struct irq_work *work) out: report_message_lost(s); - raw_spin_unlock_irqrestore(&read_lock, flags); + raw_spin_unlock_irqrestore(&safe_read_lock, flags); } /** @@ -278,6 +278,14 @@ void printk_safe_flush_on_panic(void) raw_spin_lock_init(&logbuf_lock); } + if (raw_spin_is_locked(&safe_read_lock)) { + if (num_online_cpus() > 1) + return; + + debug_locks_off(); + raw_spin_lock_init(&safe_read_lock); + } + printk_safe_flush(); } -- 2.11.0