From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4707418A6BA; Wed, 5 Feb 2025 23:50:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738799416; cv=none; b=r3ICUH4i0zJoppdLFtJpxDcZRt8mHPTWa2NEeTIQkVYP4HoVll68t3kcYy1Mv3ta2Ao0az9shMTGEnqNbV0CqcQY7IoO2m+flkiwI3WGJ+2hKkvpX+hC5TiOTWEij8evO6IItQ1cVRJUw7uFuXv53cATQet94SHbuolS1YI90n4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738799416; c=relaxed/simple; bh=WWl2S5+EyGyEtfzriFh+vpNpc+S5JQxM9/r6w/9TgLE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=S+VCnLMLKFPdTsTo9VXQRoHJ86OsF983JHkjlqtCghUYry64IFqXq+z/pe39Le6ohWhphzWlsQwKtUrJRW80PZxPsS+3a3c4QibsnDVGPta5scYnOYdBz+SeCbiWtrLM4g3bCjeRXEf1igzB/J+9CsFLBkonQVph+Z/iV7APXA8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=cXU4BkCD; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="cXU4BkCD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8892AC4CED1; Wed, 5 Feb 2025 23:50:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1738799414; bh=WWl2S5+EyGyEtfzriFh+vpNpc+S5JQxM9/r6w/9TgLE=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=cXU4BkCDbcgNWXv+x/lfkaByZWYXA39FkEEQfPHCgbHtHAzmngzxeNsk9x1GyKzxt fl2aMmIGhfcjcbyY8Iy7iJQ1Y4XMxZuQZYFoxmNWqjLkud2JCfLadwHUECgOkjbW0s 0EPiXwLEIEaxIftxlSptVrXIS+peft0832awGlz3oQtL6KUqp1aV1eEe2i2PsVG25C ssRLhMOFyRPOP73YTzjqVNJBleBE+sF4DBNrUMdsMUWyfwEw8/1Im/8KGRX729wOK2 dm5ULgdR0Vng2eL+tD0GF63QTkaVYYY9web/ZRbIJHxFuDVY4/1EX/TO56B+a0fQdU ozzJDIGKD7pbg== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 27852CE071A; Wed, 5 Feb 2025 15:50:14 -0800 (PST) Date: Wed, 5 Feb 2025 15:50:14 -0800 From: "Paul E. McKenney" To: John Ogness Cc: Petr Mladek , Sebastian Andrzej Siewior , rcu@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, rostedt@goodmis.org, Frederic Weisbecker , Thomas Gleixner , Alexei Starovoitov , Andrii Nakryiko , Mathieu Desnoyers , Masami Hiramatsu , linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH rcu v2] 4/5] rcu-tasks: Move RCU Tasks self-tests to core_initcall() Message-ID: <2a7774e4-a3fc-48d5-97b0-6f74396e7f93@paulmck-laptop> Reply-To: paulmck@kernel.org References: <20250204163409.ueObHFje@linutronix.de> <9ed4e0fd-75c4-400a-9a0b-74c68286bad3@paulmck-laptop> <84pljwi2w0.fsf@jogness.linutronix.de> <3a0ceabe-d5a0-4cb3-8343-ec56bc9bd0fd@paulmck-laptop> <84ed0c1401.fsf@jogness.linutronix.de> <841pwc11ae.fsf@jogness.linutronix.de> <84y0ykyqf6.fsf@jogness.linutronix.de> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <84y0ykyqf6.fsf@jogness.linutronix.de> On Wed, Feb 05, 2025 at 11:37:25PM +0106, John Ogness wrote: > On 2025-02-05, John Ogness wrote: > >> OK, so I don't need to add "if (IS_ENABLED(CONFIG_PREEMPT_RT))" to guard > >> it, then? > > > > For !CONFIG_PREEMPT_RT, if there are legacy consoles registered, > > pr_flush() will additionally perform a blocking lock on the > > console_lock. > > Sorry, I was just thinking about the flushing component of > pr_flush(). Later in the function it takes the console_lock even for > CONFIG_PREEMPT_RT. So please do _not_ have a guard. > > pr_flush() should never hang on the console_lock during shutdown, but if > does, that is something that will need to be debugged and fixed. > > @pmladek: Looking forward to reading your input on this. Here is an updated commit, hopefully applying your feedback correctly. Thanx, Paul ------------------------------------------------------------------------ commit 35679c18b062368855e183ee6712ca5c16145d8c Author: Paul E. McKenney Date: Wed Feb 5 12:27:23 2025 -0800 printk: Flush console log from kernel_power_off() Kernels built with CONFIG_PREEMPT_RT=y can lose significant console output and shutdown time, which hides shutdown-time RCU issues from rcutorture. Therefore, make pr_flush() public and invoke it after then last print in kernel_power_off(). [ paulmck: Apply John Ogness feedback. ] Signed-off-by: Paul E. McKenney Cc: Petr Mladek Cc: Steven Rostedt Cc: John Ogness Cc: Sergey Senozhatsky diff --git a/include/linux/printk.h b/include/linux/printk.h index 4217a9f412b2..d658d7e81bef 100644 --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -207,6 +207,7 @@ void printk_legacy_allow_panic_sync(void); extern bool nbcon_device_try_acquire(struct console *con); extern void nbcon_device_release(struct console *con); void nbcon_atomic_flush_unsafe(void); +bool pr_flush(int timeout_ms, bool reset_on_progress); #else static inline __printf(1, 0) int vprintk(const char *s, va_list args) @@ -315,6 +316,11 @@ static inline void nbcon_atomic_flush_unsafe(void) { } +static bool pr_flush(int timeout_ms, bool reset_on_progress) +{ + return true; +} + #endif bool this_cpu_in_panic(void); diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 80910bc3470c..b9699eaacf19 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2461,7 +2461,6 @@ asmlinkage __visible int _printk(const char *fmt, ...) } EXPORT_SYMBOL(_printk); -static bool pr_flush(int timeout_ms, bool reset_on_progress); static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress); #else /* CONFIG_PRINTK */ @@ -2474,7 +2473,6 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre static u64 syslog_seq; -static bool pr_flush(int timeout_ms, bool reset_on_progress) { return true; } static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress) { return true; } #endif /* CONFIG_PRINTK */ @@ -4466,7 +4464,7 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre * Context: Process context. May sleep while acquiring console lock. * Return: true if all usable printers are caught up. */ -static bool pr_flush(int timeout_ms, bool reset_on_progress) +bool pr_flush(int timeout_ms, bool reset_on_progress) { return __pr_flush(NULL, timeout_ms, reset_on_progress); } diff --git a/kernel/reboot.c b/kernel/reboot.c index a701000bab34..a84828d0757b 100644 --- a/kernel/reboot.c +++ b/kernel/reboot.c @@ -704,6 +704,7 @@ void kernel_power_off(void) migrate_to_reboot_cpu(); syscore_shutdown(); pr_emerg("Power down\n"); + pr_flush(1000, 1); kmsg_dump(KMSG_DUMP_SHUTDOWN); machine_power_off(); }