Message ID | 20221019145600.1282823-22-john.ogness@linutronix.de |
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State | New |
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[2620:137:e000::1:20]) by mx.google.com with ESMTP id l16-20020aa7cad0000000b00459c1e64776si13018144edt.412.2022.10.19.08.09.44; Wed, 19 Oct 2022 08:10:13 -0700 (PDT) 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="eDfs/FrH"; dkim=neutral (no key) header.i=@linutronix.de header.s=2020e; 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 S232115AbiJSPGx (ORCPT <rfc822;samuel.l.nystrom@gmail.com> + 99 others); Wed, 19 Oct 2022 11:06:53 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52932 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231892AbiJSPFm (ORCPT <rfc822;linux-kernel@vger.kernel.org>); Wed, 19 Oct 2022 11:05:42 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 432F6193EE9; Wed, 19 Oct 2022 07:59:07 -0700 (PDT) From: John Ogness <john.ogness@linutronix.de> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1666191373; 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=aHpEExScLzm4b3PGICcqjxP6eSShWDRVil4o7DIdRaU=; b=eDfs/FrHZ7HvnRF4atKhYEZ/pRXno8GEGAkw6IqnyiCmO75Q9sEJ6bqLoRWApu5I/kGcQh KCTzK1MrPYWFQHFbhhZ4ddIBd7thtElTQ1FhTZSvTGr+D/NiY6ja5av6esQrgKRy3JmdV3 rrRE8vZ1b74ucDPVRwBFE1RIC+RhuKL5DdLWniGfxLfcajr60p331h+dY6KdEzGysIZMdC yATsOHK/PLnHwsUFjoxiti7aJ0XxaKU0B+KQDroX00sQ4UKCeboef9oWWEJpZprSsCboLS UQL5y2A8i38TojR6bF2UMoVPjjyV/EALMD7ITlxAjhc539biNA5Q3/A88oMp9w== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1666191373; 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=aHpEExScLzm4b3PGICcqjxP6eSShWDRVil4o7DIdRaU=; b=ag8wipmZjScVK96FvYUT41NwW8W8jBS77tduneOJOnLYN8uLmQW8RkuO+x9sTyAf/SfPXA QV5RyDV2N62v9UBQ== To: Petr Mladek <pmladek@suse.com> Cc: Sergey Senozhatsky <senozhatsky@chromium.org>, Steven Rostedt <rostedt@goodmis.org>, Thomas Gleixner <tglx@linutronix.de>, linux-kernel@vger.kernel.org, Jason Wessel <jason.wessel@windriver.com>, Daniel Thompson <daniel.thompson@linaro.org>, Douglas Anderson <dianders@chromium.org>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Jiri Slaby <jirislaby@kernel.org>, kgdb-bugreport@lists.sourceforge.net, linux-serial@vger.kernel.org Subject: [PATCH printk v2 21/38] serial: kgdboc: use srcu console list iterator Date: Wed, 19 Oct 2022 17:01:43 +0206 Message-Id: <20221019145600.1282823-22-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 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: <linux-kernel.vger.kernel.org> X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1747129166988124279?= X-GMAIL-MSGID: =?utf-8?q?1747129166988124279?= |
Series |
reduce console_lock scope
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Commit Message
John Ogness
Oct. 19, 2022, 2:55 p.m. UTC
Use srcu console list iteration for safe console list traversal.
Note that configure_kgdboc() still requires the console_lock in
order to ensure that no console is in its write() callback when
its direct() callback is called. Add comments to clarify this.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
drivers/tty/serial/kgdboc.c | 21 ++++++++++++++++++---
1 file changed, 18 insertions(+), 3 deletions(-)
Comments
On Wed, Oct 19, 2022 at 05:01:43PM +0206, John Ogness wrote: > Use srcu console list iteration for safe console list traversal. > > Note that configure_kgdboc() still requires the console_lock in > order to ensure that no console is in its write() callback when > its direct() callback is called. Add comments to clarify this. > > Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
On Wed 2022-10-19 17:01:43, John Ogness wrote: > Use srcu console list iteration for safe console list traversal. > > Note that configure_kgdboc() still requires the console_lock in > order to ensure that no console is in its write() callback when > its direct() callback is called. Add comments to clarify this. s/direct()/device()/ Do you know about such requirements or is it just a conservative approach, please? I ask because the comment in the code says "may assume". Anyway, this would deserve a comment why the SRCU list iteration is needed even when console_lock() is needed as well. The reason is that further patches are going to synchronize console_list manipulation with another lock and console_lock() will be used only to serialize accessing con->write() callbacks. Best Regards, Petr > Signed-off-by: John Ogness <john.ogness@linutronix.de> > --- > drivers/tty/serial/kgdboc.c | 21 ++++++++++++++++++--- > 1 file changed, 18 insertions(+), 3 deletions(-) > > diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c > index b17aa7e49894..e9d3f8c6e3dc 100644 > --- a/drivers/tty/serial/kgdboc.c > +++ b/drivers/tty/serial/kgdboc.c > @@ -171,6 +171,7 @@ static int configure_kgdboc(void) > int err = -ENODEV; > char *cptr = config; > struct console *cons; > + int cookie; > > if (!strlen(config) || isspace(config[0])) { > err = 0; > @@ -193,8 +194,14 @@ static int configure_kgdboc(void) > if (!p) > goto noconfig; > > + /* > + * Stop console printing because the device() callback may > + * assume the console is not within its write() callback. > + */ > console_lock(); > - for_each_console(cons) { > + > + cookie = console_srcu_read_lock(); > + for_each_console_srcu(cons) { > int idx; > if (cons->device && cons->device(cons, &idx) == p && > idx == tty_line) { > @@ -202,6 +209,8 @@ static int configure_kgdboc(void) > break; > } > } > + console_srcu_read_unlock(cookie); > + > console_unlock(); > > kgdb_tty_driver = p; > @@ -451,6 +460,7 @@ static void kgdboc_earlycon_pre_exp_handler(void) > { > struct console *con; > static bool already_warned; > + int cookie; > > if (already_warned) > return; > @@ -463,9 +473,14 @@ static void kgdboc_earlycon_pre_exp_handler(void) > * serial drivers might be OK with this, print a warning once per > * boot if we detect this case. > */ > - for_each_console(con) > + cookie = console_srcu_read_lock(); > + for_each_console_srcu(con) { > if (con == kgdboc_earlycon_io_ops.cons) > - return; > + break; > + } > + console_srcu_read_unlock(cookie); > + if (con) > + return; > > already_warned = true; > pr_warn("kgdboc_earlycon is still using bootconsole\n"); > -- > 2.30.2
Hi, On Fri, Oct 21, 2022 at 8:09 AM Petr Mladek <pmladek@suse.com> wrote: > > On Wed 2022-10-19 17:01:43, John Ogness wrote: > > Use srcu console list iteration for safe console list traversal. > > > > Note that configure_kgdboc() still requires the console_lock in > > order to ensure that no console is in its write() callback when > > its direct() callback is called. Add comments to clarify this. > > s/direct()/device()/ > > Do you know about such requirements or is it just > a conservative approach, please? > > I ask because the comment in the code says "may assume". > > > Anyway, this would deserve a comment why the SRCU list iteration is > needed even when console_lock() is needed as well. > > The reason is that further patches are going to synchronize > console_list manipulation with another lock and console_lock() > will be used only to serialize accessing con->write() callbacks. I had the same concern. I'll note that at the end of the series the documentation for console_lock() still says: * Acquires a lock which guarantees that the caller has * exclusive access to the console system. That seems to imply (at least to me) that if you're holding console_lock() there's no need to hold the SRCU lock. -Doug
diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c index b17aa7e49894..e9d3f8c6e3dc 100644 --- a/drivers/tty/serial/kgdboc.c +++ b/drivers/tty/serial/kgdboc.c @@ -171,6 +171,7 @@ static int configure_kgdboc(void) int err = -ENODEV; char *cptr = config; struct console *cons; + int cookie; if (!strlen(config) || isspace(config[0])) { err = 0; @@ -193,8 +194,14 @@ static int configure_kgdboc(void) if (!p) goto noconfig; + /* + * Stop console printing because the device() callback may + * assume the console is not within its write() callback. + */ console_lock(); - for_each_console(cons) { + + cookie = console_srcu_read_lock(); + for_each_console_srcu(cons) { int idx; if (cons->device && cons->device(cons, &idx) == p && idx == tty_line) { @@ -202,6 +209,8 @@ static int configure_kgdboc(void) break; } } + console_srcu_read_unlock(cookie); + console_unlock(); kgdb_tty_driver = p; @@ -451,6 +460,7 @@ static void kgdboc_earlycon_pre_exp_handler(void) { struct console *con; static bool already_warned; + int cookie; if (already_warned) return; @@ -463,9 +473,14 @@ static void kgdboc_earlycon_pre_exp_handler(void) * serial drivers might be OK with this, print a warning once per * boot if we detect this case. */ - for_each_console(con) + cookie = console_srcu_read_lock(); + for_each_console_srcu(con) { if (con == kgdboc_earlycon_io_ops.cons) - return; + break; + } + console_srcu_read_unlock(cookie); + if (con) + return; already_warned = true; pr_warn("kgdboc_earlycon is still using bootconsole\n");