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 6A779C4332F for ; Wed, 19 Oct 2022 15:07:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229912AbiJSPH3 (ORCPT ); Wed, 19 Oct 2022 11:07:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53454 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230430AbiJSPFr (ORCPT ); Wed, 19 Oct 2022 11:05:47 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8F823220FF for ; Wed, 19 Oct 2022 07:59:28 -0700 (PDT) From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1666191377; 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=Dg+eirxPEtXsZsT+nvxwn7klIpJXP2S7/lYWcLQsq5o=; b=MPYjmlBAQJxd8Rggng1mxW4di7b7xYOCjLNGRWpjRItXh3zWEx5mIiT5FQKnOr3++nqdFC pe86OdsADSBSH5eHo+UuSujM5JBEBpxz4EqDYayBdbpNcMLU9lC9OlX+CxEuViL3w0XxBH xw8pxjWFvUNr5Edl/oW9ZbygohqM9mxtghTUvuuRVvuUhF+m9H0bWLFljDXTwz8k7NuXOO sCTinHr3ebMbna/ZdTfsspODBgffQYwaNnL2PKRKsQR5J7KHns5Ztl30N8PQHMgTWj18rj 6HnkVcBl5OkAIL3PZyV8kgLNYcAjsfCjNaihlBxF2F8vGFgwMhFh9yuFifCIOQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1666191377; 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=Dg+eirxPEtXsZsT+nvxwn7klIpJXP2S7/lYWcLQsq5o=; b=EtIY4tyi7hLpay8rDK+lcQKRKX8CIAg4otKaMkH3lPH6wnLHsrvZ4XcHsVGirSMNMsusC9 780jjF0WOKRvUkDg== To: Petr Mladek Cc: Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org Subject: [PATCH printk v2 27/38] printk: console_flush_all: use srcu console list iterator Date: Wed, 19 Oct 2022 17:01:49 +0206 Message-Id: <20221019145600.1282823-28-john.ogness@linutronix.de> In-Reply-To: <20221019145600.1282823-1-john.ogness@linutronix.de> References: <20221019145600.1282823-1-john.ogness@linutronix.de> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Guarantee safe iteration of the console list by using SRCU. Note that in the case of a handover, the SRCU read lock is also released. This is documented in the function description and as comments in the code. It is a bit tricky, but this preserves the lockdep lock ordering for the context handing over the console_lock: console_lock() | mutex_acquire(&console_lock_dep_map) <-- console lock | console_unlock() | console_flush_all() | | srcu_read_lock(&console_srcu) <-- srcu lock | | console_emit_next_record() | | | console_lock_spinning_disable_and_check() | | | | srcu_read_unlock(&console_srcu) <-- srcu unlock | | | | mutex_release(&console_lock_dep_map) <-- console unlock Signed-off-by: John Ogness --- kernel/printk/printk.c | 38 ++++++++++++++++++++++++++++---------- 1 file changed, 28 insertions(+), 10 deletions(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 7ff2fc75fc3b..c4d5d58b5977 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -1851,7 +1851,7 @@ static void console_lock_spinning_enable(void) * * Return: 1 if the lock rights were passed, 0 otherwise. */ -static int console_lock_spinning_disable_and_check(void) +static int console_lock_spinning_disable_and_check(int cookie) { int waiter; @@ -1870,6 +1870,12 @@ static int console_lock_spinning_disable_and_check(void) spin_release(&console_owner_dep_map, _THIS_IP_); + /* + * Preserve lockdep lock ordering. Release the SRCU read lock before + * releasing the console_lock. + */ + console_srcu_read_unlock(cookie); + /* * Hand off console_lock to waiter. The waiter will perform * the up(). After this, the waiter is the console_lock owner. @@ -2353,7 +2359,7 @@ static ssize_t msg_print_ext_body(char *buf, size_t size, char *text, size_t text_len, struct dev_printk_info *dev_info) { return 0; } static void console_lock_spinning_enable(void) { } -static int console_lock_spinning_disable_and_check(void) { return 0; } +static int console_lock_spinning_disable_and_check(int cookie) { return 0; } static void call_console_driver(struct console *con, const char *text, size_t len, char *dropped_text) { @@ -2695,8 +2701,8 @@ static void __console_unlock(void) * DROPPED_TEXT_MAX. Otherwise @dropped_text must be NULL. * * @handover will be set to true if a printk waiter has taken over the - * console_lock, in which case the caller is no longer holding the - * console_lock. Otherwise it is set to false. + * console_lock, in which case the caller is no longer holding both the + * console_lock and the SRCU read lock. Otherwise it is set to false. * * Returns false if the given console has no next record to print, otherwise * true. @@ -2704,7 +2710,7 @@ static void __console_unlock(void) * Requires the console_lock. */ static bool console_emit_next_record(struct console *con, char *text, char *ext_text, - char *dropped_text, bool *handover) + char *dropped_text, bool *handover, int cookie) { static int panic_console_dropped; struct printk_info info; @@ -2764,7 +2770,7 @@ static bool console_emit_next_record(struct console *con, char *text, char *ext_ con->seq++; - *handover = console_lock_spinning_disable_and_check(); + *handover = console_lock_spinning_disable_and_check(cookie); printk_safe_exit_irqrestore(flags); skip: return true; @@ -2801,6 +2807,7 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove bool any_usable = false; struct console *con; bool any_progress; + int cookie; *next_seq = 0; *handover = false; @@ -2808,7 +2815,8 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove do { any_progress = false; - for_each_console(con) { + cookie = console_srcu_read_lock(); + for_each_console_srcu(con) { bool progress; if (!console_is_usable(con)) @@ -2819,12 +2827,17 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove /* Extended consoles do not print "dropped messages". */ progress = console_emit_next_record(con, &text[0], &ext_text[0], NULL, - handover); + handover, cookie); } else { progress = console_emit_next_record(con, &text[0], NULL, &dropped_text[0], - handover); + handover, cookie); } + + /* + * If a handover has occurred, the SRCU read lock + * is already released. + */ if (*handover) return false; @@ -2838,14 +2851,19 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove /* Allow panic_cpu to take over the consoles safely. */ if (abandon_console_lock_in_panic()) - return false; + goto abandon; if (do_cond_resched) cond_resched(); } + console_srcu_read_unlock(cookie); } while (any_progress); return any_usable; + +abandon: + console_srcu_read_unlock(cookie); + return false; } /** -- 2.30.2