From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on gnuweeb.org X-Spam-Level: X-Spam-Status: No, score=-1.9 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,DKIM_VALID_EF,INVALID_DATE_TZ_ABSURD,RCVD_IN_DNSWL_MED, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.6 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by gnuweeb.org (Postfix) with ESMTPS id 303FD80927 for ; Thu, 1 Sep 2022 09:12:23 +0000 (UTC) Authentication-Results: gnuweeb.org; dkim=pass (2048-bit key; secure) header.d=linutronix.de header.i=@linutronix.de header.a=rsa-sha256 header.s=2020 header.b=UMaLYHKJ; dkim=pass header.d=linutronix.de header.i=@linutronix.de header.a=ed25519-sha256 header.s=2020e header.b=z0qgClFF; dkim-atps=neutral From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1662023540; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=kaRumsH3KDmkPnek0I9ClyHltDQl827/GSI2YJ5tGmk=; b=UMaLYHKJYk7R0Y8kbntlx28LDmUpMYh6Im3Bftl4gjEQBTpMoLzrwLCy0mgE41F72kvM8W 0JcaF+RNRxkygEQvcQCOb+a5lzUum4ZR3SwyCx+nJzoAxF2pE8iCecKLsb5ScCMyxc49H8 Updrr2/BSgHUGoQx6jcZq+sqWpvohuvarXhWstR9Xl0F0042eHdL/61XaG/dU525vNqyXU zXe5C2rXMllqWtMxszk4DI5GvoZUXXPNU3ShV9+bgA/zBQZb5KauvxdNSvGVvW5lXDHADU z7V/2LFOFiN8MtpIMgB2PkA3mW7oNVR0uwvwlkN/WJpWKmk8/uOlUzTB3FqNcg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1662023540; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=kaRumsH3KDmkPnek0I9ClyHltDQl827/GSI2YJ5tGmk=; b=z0qgClFFWJ0+UUaCJLAVasOOCjJjZx02ljJShf+ooWSzp3OoVUqiVtiK8Xc40jCR63GvSW Qz1CF+qoidhmrTAA== To: "Paul E. McKenney" , linux-kernel@vger.kernel.org Cc: gwml@vger.gnuweeb.org, kernel-team@fb.com, w@lwt.eu, "Paul E. McKenney" , Petr Mladek , Sergey Senozhatsky , Steven Rostedt Subject: Re: [PATCH rcu 1/2] torture: Optionally flush printk() buffers before powering off In-Reply-To: <20220831182148.2698489-2-paulmck@kernel.org> References: <20220831182113.GA2697286@paulmck-ThinkPad-P17-Gen-1> <20220831182148.2698489-2-paulmck@kernel.org> Date: Thu, 01 Sep 2022 11:18:20 +0206 Message-ID: <87tu5rfogb.fsf@jogness.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain List-Id: Added CC the rest of the printk folks since this would be the first use of pr_flush() outside of the printk subsystem. And it is a controversial usage, since it is used to work around potential (future) bugs in printk. On 2022-08-31, "Paul E. McKenney" wrote: > The rcutorture test suite produces quite a bit of console output at > the end of a test. This means that the new-in-2022 printk() kthreads > are likely to be in the process of flushing output at the time of the > torture_shutdown() function's call to kernel_power_off(). Normally, > rcutorture relies on printk() to flush any pending output upon shutdown, > the better to detect bugs in this area, for example, the one introduced > by 8e274732115f ("printk: extend console_lock for per-console locking"). > However, once such a bug is detected and reported, it is necessary to > test the rest of the system, without noise from the already-reported bug. Since the printk kthread implementation has been reverted, this is no longer an issue. When a kthread implementation is re-introduced, this issue will need to have been considered and handled. IMHO this patch is premature at this time and hopefully will never become necessary (in the form of a bug workaround). > This commit therefore adds a torture.printk_shutdown_bug_workaround > kernel parameter, which causes torture_shutdown() to invoke pr_flush(), > and print an informative message on the console, immediately before > invoking kernel_power_off(). When this kernel parameter is not specified, > it is up to printk() to flush its own buffers. > > Suggested-by: John Ogness > Signed-off-by: Paul E. McKenney > --- > Documentation/admin-guide/kernel-parameters.txt | 6 ++++++ > kernel/torture.c | 7 +++++++ > 2 files changed, 13 insertions(+) > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index d7f30902fda02..ba1b8776aab83 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -6143,6 +6143,12 @@ > are running concurrently, especially on systems > with rotating-rust storage. > > + torture.printk_shutdown_bug_workaround= [KNL] > + Execute pr_flush(1000, true) just before invoking > + kernel_power_off() to work around any bugs that > + might prevent printk() from flushing its buffers > + at shutdown time. > + > torture.verbose_sleep_frequency= [KNL] > Specifies how many verbose printk()s should be > emitted between each sleep. The default of zero > diff --git a/kernel/torture.c b/kernel/torture.c > index 789aeb0e1159c..7cd2016b02076 100644 > --- a/kernel/torture.c > +++ b/kernel/torture.c > @@ -48,6 +48,9 @@ module_param(disable_onoff_at_boot, bool, 0444); > static bool ftrace_dump_at_shutdown; > module_param(ftrace_dump_at_shutdown, bool, 0444); > > +static bool printk_shutdown_bug_workaround; > +module_param(printk_shutdown_bug_workaround, bool, 0444); > + > static int verbose_sleep_frequency; > module_param(verbose_sleep_frequency, int, 0444); > > @@ -651,6 +654,10 @@ static int torture_shutdown(void *arg) > VERBOSE_TOROUT_STRING("No torture_shutdown_hook(), skipping."); > if (ftrace_dump_at_shutdown) > rcu_ftrace_dump(DUMP_ALL); > + if (printk_shutdown_bug_workaround) { > + pr_info("%s: Flushing printk() buffers at power-down time.\n", __func__); > + pr_flush(1000, true); > + } > kernel_power_off(); /* Shut down the system. */ > return 0; > } > -- > 2.31.1.189.g2e36527f23 John Ogness