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=-6.2 required=5.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_HI,SPF_HELO_NONE, SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by gnuweeb.org (Postfix) with ESMTPS id 1C5A980866 for ; Thu, 1 Sep 2022 10:17:42 +0000 (UTC) Authentication-Results: gnuweeb.org; dkim=pass (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20201202 header.b=pPK95Zqw; dkim-atps=neutral Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 4AF3761C16; Thu, 1 Sep 2022 10:17:41 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id AF0EFC433C1; Thu, 1 Sep 2022 10:17:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1662027460; bh=lEsecR9/MhQrB8RJTlGXlTDanfUfsZB9RoqMuYg27TE=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=pPK95ZqwJxoq7d/isyzZEpNdJN6BOYFln6Zkf9b1+DHwe4qBgUMOn3uqHNeek0h8Q IWV8mHognZcqHTrMIZwk14btCeUkDPzgq3TdLoy3ZL9zNbTbvSpZZr4Xp2syU7JVkk MxncaHuhsg1FkwTykqwb15HIgFK/e18Jc3W2BrtvqlkyQcRSPpMZ7fzr8WzAqcIX9J o5xxs21jtEghhqUuhPXcNaOtkH7E5bGIEMcclKHGPq+6IjBogiCzJ57xtFFSjtnxY3 bQFiHQ5kpcxaSt3Ju14A2OfydAyQMkkCq+uttXG8VfVKZVuwz6FJjmBlwR7oiS0X6K bhVIX4bZEtVwA== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 36DEF5C06C8; Thu, 1 Sep 2022 03:17:40 -0700 (PDT) Date: Thu, 1 Sep 2022 03:17:40 -0700 From: "Paul E. McKenney" To: John Ogness Cc: linux-kernel@vger.kernel.org, gwml@vger.gnuweeb.org, kernel-team@fb.com, w@lwt.eu, Petr Mladek , Sergey Senozhatsky , Steven Rostedt Subject: Re: [PATCH rcu 1/2] torture: Optionally flush printk() buffers before powering off Message-ID: <20220901101740.GP6159@paulmck-ThinkPad-P17-Gen-1> Reply-To: paulmck@kernel.org References: <20220831182113.GA2697286@paulmck-ThinkPad-P17-Gen-1> <20220831182148.2698489-2-paulmck@kernel.org> <87tu5rfogb.fsf@jogness.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87tu5rfogb.fsf@jogness.linutronix.de> List-Id: On Thu, Sep 01, 2022 at 11:18:20AM +0206, John Ogness wrote: > 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). Very well, I will drop it, for the time being, anyway. ;-) Thanx, Paul > > 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