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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B3F79C433F5 for ; Wed, 30 Mar 2022 11:58:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344421AbiC3MAf (ORCPT ); Wed, 30 Mar 2022 08:00:35 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33054 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344703AbiC3Lx3 (ORCPT ); Wed, 30 Mar 2022 07:53:29 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5027E26D102; Wed, 30 Mar 2022 04:49:28 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id BFBB36162C; Wed, 30 Mar 2022 11:49:22 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6050CC36AEA; Wed, 30 Mar 2022 11:49:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1648640962; bh=jKdMbV/aDuitwGBnxxb5mfw7Z300Q/lkHFHXWOjhUgg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=eBUad8qUJdXyO4e/11ZOkj7xNlvZpoybITuT/a4qVOBhEKa1T8ob1d/OoAmelv+EQ hXWAxmGD9prsZDL7nyRVwfgHIBMR7DZSozVHU/kLRIBaBJjUz3fz9O71Gc+eKgaWje IgKdL2ZoH4FQF8+cCoJ3yk/rfuPH8XaZ9nhQmzyuaR6Gx1QRrkDiZkc6TUtBe6NKUY dpyIjb598o+SfoxQ8f9nbG73ORMxpgVXc1jQEEphe6TsZDUqHFlm8xLpfFKier9ZGA 0HSq4UK/1VTX3YPA9E+ixXjCvNH9nMHNfbMrD2EFSHPH3N1S1sM9bO1TdacNpID8cE RCHdUSeQU+Qdw== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Stephen Brennan , Petr Mladek , Sergey Senozhatsky , Sasha Levin , linux@roeck-us.net Subject: [PATCH AUTOSEL 5.16 32/59] printk: Avoid livelock with heavy printk during panic Date: Wed, 30 Mar 2022 07:48:04 -0400 Message-Id: <20220330114831.1670235-32-sashal@kernel.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20220330114831.1670235-1-sashal@kernel.org> References: <20220330114831.1670235-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Stephen Brennan [ Upstream commit 13fb0f74d7029df3b8137f11ef955e578a4a4a60 ] During panic(), if another CPU is writing heavily the kernel log (e.g. via /dev/kmsg), then the panic CPU may livelock writing out its messages to the console. Note when too many messages are dropped during panic and suppress further printk, except from the panic CPU. This could result in some important messages being dropped. However, messages are already being dropped, so this approach at least prevents a livelock. Reviewed-by: Petr Mladek Signed-off-by: Stephen Brennan Reviewed-by: Sergey Senozhatsky Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20220202171821.179394-4-stephen.s.brennan@oracle.com Signed-off-by: Sasha Levin --- kernel/printk/printk.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index e3d986dd49a1..f7c4c53a2c35 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -93,6 +93,12 @@ EXPORT_SYMBOL_GPL(console_drivers); */ int __read_mostly suppress_printk; +/* + * During panic, heavy printk by other CPUs can delay the + * panic and risk deadlock on console resources. + */ +int __read_mostly suppress_panic_printk; + #ifdef CONFIG_LOCKDEP static struct lockdep_map console_lock_dep_map = { .name = "console_lock" @@ -2223,6 +2229,10 @@ asmlinkage int vprintk_emit(int facility, int level, if (unlikely(suppress_printk)) return 0; + if (unlikely(suppress_panic_printk) && + atomic_read(&panic_cpu) != raw_smp_processor_id()) + return 0; + if (level == LOGLEVEL_SCHED) { level = LOGLEVEL_DEFAULT; in_sched = true; @@ -2608,6 +2618,7 @@ void console_unlock(void) { static char ext_text[CONSOLE_EXT_LOG_MAX]; static char text[CONSOLE_LOG_MAX]; + static int panic_console_dropped; unsigned long flags; bool do_cond_resched, retry; struct printk_info info; @@ -2662,6 +2673,10 @@ void console_unlock(void) if (console_seq != r.info->seq) { console_dropped += r.info->seq - console_seq; console_seq = r.info->seq; + if (panic_in_progress() && panic_console_dropped++ > 10) { + suppress_panic_printk = 1; + pr_warn_once("Too many dropped messages. Suppress messages on non-panic CPUs to prevent livelock.\n"); + } } if (suppress_message_printing(r.info->level)) { -- 2.34.1