From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 35A311D6A7 for ; Wed, 20 Sep 2023 11:57:19 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A4E24C433C9; Wed, 20 Sep 2023 11:57:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1695211039; bh=6CqAcjaDl/vEh1wlRMBzRNT/Mmv4MSM91u5A2jx5zK0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ywWIq/sVM5HrVJWnPGrn1GysKFzDQODTRkUZXBoMyoa9XKaPfsAhwlJ6wrIWqkJh+ y4iD/JUke7kdolIxamp3DbMs0Ox4bFKPNrho6iLXJUUFJ7+zqavXp9zzmuWV5aY7bv ATIlpqYbg1RiYPucvUHW7CmJp2S3RSDMpRywNncg= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, John Ogness , Sergey Senozhatsky , Petr Mladek , Sasha Levin Subject: [PATCH 6.1 086/139] printk: Keep non-panic-CPUs out of console lock Date: Wed, 20 Sep 2023 13:30:20 +0200 Message-ID: <20230920112838.836388090@linuxfoundation.org> X-Mailer: git-send-email 2.42.0 In-Reply-To: <20230920112835.549467415@linuxfoundation.org> References: <20230920112835.549467415@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: John Ogness [ Upstream commit 51a1d258e50e03a0216bf42b6af9ff34ec402ac1 ] When in a panic situation, non-panic CPUs should avoid holding the console lock so as not to contend with the panic CPU. This is already implemented with abandon_console_lock_in_panic(), which is checked after each printed line. However, non-panic CPUs should also avoid trying to acquire the console lock during a panic. Modify console_trylock() to fail and console_lock() to block() when called from a non-panic CPU during a panic. Signed-off-by: John Ogness Reviewed-by: Sergey Senozhatsky Reviewed-by: Petr Mladek Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20230717194607.145135-4-john.ogness@linutronix.de Signed-off-by: Sasha Levin --- kernel/printk/printk.c | 45 ++++++++++++++++++++++++------------------ 1 file changed, 26 insertions(+), 19 deletions(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index e4f1e7478b521..4b9429f3fd6d8 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2552,6 +2552,25 @@ static int console_cpu_notify(unsigned int cpu) return 0; } +/* + * Return true when this CPU should unlock console_sem without pushing all + * messages to the console. This reduces the chance that the console is + * locked when the panic CPU tries to use it. + */ +static bool abandon_console_lock_in_panic(void) +{ + if (!panic_in_progress()) + return false; + + /* + * We can use raw_smp_processor_id() here because it is impossible for + * the task to be migrated to the panic_cpu, or away from it. If + * panic_cpu has already been set, and we're not currently executing on + * that CPU, then we never will be. + */ + return atomic_read(&panic_cpu) != raw_smp_processor_id(); +} + /** * console_lock - lock the console system for exclusive use. * @@ -2564,6 +2583,10 @@ void console_lock(void) { might_sleep(); + /* On panic, the console_lock must be left to the panic cpu. */ + while (abandon_console_lock_in_panic()) + msleep(1000); + down_console_sem(); if (console_suspended) return; @@ -2582,6 +2605,9 @@ EXPORT_SYMBOL(console_lock); */ int console_trylock(void) { + /* On panic, the console_lock must be left to the panic cpu. */ + if (abandon_console_lock_in_panic()) + return 0; if (down_trylock_console_sem()) return 0; if (console_suspended) { @@ -2600,25 +2626,6 @@ int is_console_locked(void) } EXPORT_SYMBOL(is_console_locked); -/* - * Return true when this CPU should unlock console_sem without pushing all - * messages to the console. This reduces the chance that the console is - * locked when the panic CPU tries to use it. - */ -static bool abandon_console_lock_in_panic(void) -{ - if (!panic_in_progress()) - return false; - - /* - * We can use raw_smp_processor_id() here because it is impossible for - * the task to be migrated to the panic_cpu, or away from it. If - * panic_cpu has already been set, and we're not currently executing on - * that CPU, then we never will be. - */ - return atomic_read(&panic_cpu) != raw_smp_processor_id(); -} - /* * Check if the given console is currently capable and allowed to print * records. -- 2.40.1