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[2620:137:e000::1:20]) by mx.google.com with ESMTP id 74-20020a63024d000000b004403d4f1f6esi10017797pgc.458.2022.11.14.08.30.46; Mon, 14 Nov 2022 08:31:21 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@linutronix.de header.s=2020 header.b=XQ9KB4oe; dkim=neutral (no key) header.i=@linutronix.de header.s=2020e header.b=RTsdtTus; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=linutronix.de Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237639AbiKNQaZ (ORCPT + 99 others); Mon, 14 Nov 2022 11:30:25 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35748 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237554AbiKNQ3q (ORCPT ); Mon, 14 Nov 2022 11:29:46 -0500 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A2612116D for ; Mon, 14 Nov 2022 08:29:41 -0800 (PST) From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1668443380; 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=dmQgD+t+Pywrubu3H0mhuWuMaWs++GAlupQRHdINU0E=; b=XQ9KB4oeyyyeCvUXMGQ2bqZFv93YVz5KGSl5A172siQS+8OuGoVz7/F/KnpUIaynkz30Dp kR2kETCMrLKZgEatVBs6HhoMFGvz8KgezFKHF9fyJDmnDbCfNsbmrmczlEVLF9Ry29VGvQ t8G8SOFz7fWVamv5nnHRbw2w4/WvrFzdv2qwZEsXXZNG+fqHiGHM+ldv0yOUhM9AB7HC+n PqdpZ6hgVYTjCqEWW9jv1c2vNJYWHDSw6YOV+e11DsrQlKDkrQr12iNfRLDQlPmHr/jkuY gujwc6Rq9oLYttRJ00U3/vfnvy6Q1XE4fL5/+X8lKDr5c21zlTaWuyeQuf7+hw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1668443380; 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=dmQgD+t+Pywrubu3H0mhuWuMaWs++GAlupQRHdINU0E=; b=RTsdtTusacNEWE15rK5zI5JAuKscbSo2PVn8TlR/kHK5kLMWgXvw5/Ga525pquU1vcOsps JLpNpTN3W+2dYvBA== To: Petr Mladek Cc: Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org, Jason Wessel , Daniel Thompson , Douglas Anderson , Luis Chamberlain , Aaron Tomlin , kgdb-bugreport@lists.sourceforge.net Subject: [PATCH printk v4 13/39] kdb: use srcu console list iterator Date: Mon, 14 Nov 2022 17:35:06 +0106 Message-Id: <20221114162932.141883-14-john.ogness@linutronix.de> In-Reply-To: <20221114162932.141883-1-john.ogness@linutronix.de> References: <20221114162932.141883-1-john.ogness@linutronix.de> MIME-Version: 1.0 X-Spam-Status: No, score=-3.9 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,INVALID_DATE_TZ_ABSURD, RCVD_IN_DNSWL_MED,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1749489792525121554?= X-GMAIL-MSGID: =?utf-8?q?1749489792525121554?= Guarantee safe iteration of the console list by using SRCU. Signed-off-by: John Ogness Reviewed-by: Petr Mladek Reviewed-by: Aaron Tomlin --- kernel/debug/kdb/kdb_io.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c index 67d3c48a1522..5c7e9ba7cd6b 100644 --- a/kernel/debug/kdb/kdb_io.c +++ b/kernel/debug/kdb/kdb_io.c @@ -545,6 +545,7 @@ static void kdb_msg_write(const char *msg, int msg_len) { struct console *c; const char *cp; + int cookie; int len; if (msg_len == 0) @@ -558,8 +559,20 @@ static void kdb_msg_write(const char *msg, int msg_len) cp++; } - for_each_console(c) { - if (!(c->flags & CON_ENABLED)) + /* + * The console_srcu_read_lock() only provides safe console list + * traversal. The use of the ->write() callback relies on all other + * CPUs being stopped at the moment and console drivers being able to + * handle reentrance when @oops_in_progress is set. + * + * There is no guarantee that every console driver can handle + * reentrance in this way; the developer deploying the debugger + * is responsible for ensuring that the console drivers they + * have selected handle reentrance appropriately. + */ + cookie = console_srcu_read_lock(); + for_each_console_srcu(c) { + if (!(console_srcu_read_flags(c) & CON_ENABLED)) continue; if (c == dbg_io_ops->cons) continue; @@ -577,6 +590,7 @@ static void kdb_msg_write(const char *msg, int msg_len) --oops_in_progress; touch_nmi_watchdog(); } + console_srcu_read_unlock(cookie); } int vkdb_printf(enum kdb_msgsrc src, const char *fmt, va_list ap)