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 7D975EB64DC for ; Mon, 17 Jul 2023 19:46:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231685AbjGQTqV (ORCPT ); Mon, 17 Jul 2023 15:46:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41532 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230139AbjGQTqN (ORCPT ); Mon, 17 Jul 2023 15:46:13 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 83738134 for ; Mon, 17 Jul 2023 12:46:12 -0700 (PDT) From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1689623171; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ebq6l34l2HQ4NpuglsKT6EmyQrUsETfJZCfMOAes7xM=; b=h2Phg3vq9RX6pbtYd4TTqsothRQPA9cc8OMkVJvDNv6uVhzae5XPjK+j36HSgHgdDcVbqX +Nw5zHr++J17VgrVcj+UOJZtQ/0sKuPbkA7SAZwEbRxp2+Ns9ymjmo8uj6Kva+JkAfjxGm 5NdT5www9+FFuGh4qLmcagc89ij/rm8xFnRZuDWpQbonxdnIxJIbqR0fOT34vUPGtrTQcZ kT7jKuqR3jochM9fqOBtX0VOKBMULGyiYCRUlGvNe43NEoYjqca7RQXbm8Q5MQe16S1KiB SCZjYGV0V7fVIzJBOZ1hV0+wlrKjzj29nMfVxg0ZigmdRtPy6lRFP6pOpalsgw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1689623171; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ebq6l34l2HQ4NpuglsKT6EmyQrUsETfJZCfMOAes7xM=; b=jVReI8sdiuzF8KIatWI0DIlhvH1JYFe3Vod7rkgII32uVQ4VfjYCzXDuD0uC65i+ahX0vC PQn2VAozBSXtCvBg== To: Petr Mladek Cc: Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org Subject: [PATCH printk v3 3/7] printk: Keep non-panic-CPUs out of console lock Date: Mon, 17 Jul 2023 21:52:03 +0206 Message-Id: <20230717194607.145135-4-john.ogness@linutronix.de> In-Reply-To: <20230717194607.145135-1-john.ogness@linutronix.de> References: <20230717194607.145135-1-john.ogness@linutronix.de> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- 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 7aa9dbee12e8..7219991885e6 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2583,6 +2583,25 @@ 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 - block the console subsystem from printing * @@ -2595,6 +2614,10 @@ 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; @@ -2613,6 +2636,9 @@ 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) { @@ -2631,25 +2657,6 @@ 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. -- 2.30.2