From nobody Wed Dec 17 23:28:28 2025 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (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 5E4411DF668 for ; Tue, 20 Aug 2024 06:30:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724135417; cv=none; b=DT78jy2S1wphNH4/yhrpJiCJ0LQeHkojDF+FLtPiYLgfQLK0DW/DSiNZrnaVcHeIs4zFF7T3pgHkbQTqbOGq6toRFgV/yHTnoahjPwD+zDtauydE7t37pKsQ81svjFpHysAicc3Bn/eFbD3isYGK79Wp8RJwiKbxCkQ2yI9Gqvc= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724135417; c=relaxed/simple; bh=HHI7Ear+fg+AU28kKXg5E+dDl5c0aRK9t5J8KusTUxA=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=uKjfKqf8V6Wzm1FAMF7vAY/MVdt+e35UIZ6cqD4aByX5lA1LYHkRoZwAxS6OCAOTPOp7dYhsQzcvfMdJYxnAZflZeDvRqyn88XgbohDeQ2cHm06e+Oqg3GPDMmzMm/QBFuDzXFF6m9T7CiAsKjjvDejUehmA3AoQ8QfxuMyfaUI= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=L7q/vm8u; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=LTQccK5o; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="L7q/vm8u"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="LTQccK5o" From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1724135414; 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=wg6fe3txNni7ErFu43onKGcRIq9DFbnTuItwd0arL7c=; b=L7q/vm8uB6pdEm+D4eCDJQtARlGJlea8Tnt8Q64X5IoN6i66Kx0ttQv4yTfSpB75KmbWFI yOAuqlP76pIT/ylfmkJc/pYZkWOdE5cQUO5+0jltML6Pd4mEdsAdvH0d+Yy7BujK0E8TFw WbMEMWQPZTnloedyziZr0hhAxbdKnPxbjGPcBQpyDI2Fc2q4O4q1uqJTsxLa7ahaHriyF0 yAI/jdofmaSQBNwpKQhwexWbyARo+vvrqhkdgZdz4HHM5g2jHiEUCQ26a6OYSX7wJsxkTY RiOi8rhkG9de41TIZ727gfSgCEY6zJGV6N99a2Vzrkv4rsvpew+2FUK+KtQ2Yg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1724135414; 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=wg6fe3txNni7ErFu43onKGcRIq9DFbnTuItwd0arL7c=; b=LTQccK5oaUf+1W3MgTtubcL05S1luQTlqPFNiel2SgKwnQiMIy9Bo4fIMkI8cogLKLq0/p /Ml0hpqGzcXSHLAg== To: Petr Mladek Cc: Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org Subject: [PATCH printk v8 27/35] printk: Avoid console_lock dance if no legacy or boot consoles Date: Tue, 20 Aug 2024 08:35:53 +0206 Message-Id: <20240820063001.36405-28-john.ogness@linutronix.de> In-Reply-To: <20240820063001.36405-1-john.ogness@linutronix.de> References: <20240820063001.36405-1-john.ogness@linutronix.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Currently the console lock is used to attempt legacy-type printing even if there are no legacy or boot consoles registered. If no such consoles are registered, the console lock does not need to be taken. Add tracking of legacy console registration and use it with boot console tracking to avoid unnecessary code paths, i.e. do not use the console lock if there are no boot consoles and no legacy consoles. Signed-off-by: John Ogness Reviewed-by: Petr Mladek --- kernel/printk/printk.c | 39 ++++++++++++++++++++++++++++++++++----- 1 file changed, 34 insertions(+), 5 deletions(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index c6e633329e4d..b3ddcf39a53c 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -463,6 +463,13 @@ static int console_msg_format =3D MSG_FORMAT_DEFAULT; /* syslog_lock protects syslog_* variables and write access to clear_seq. = */ static DEFINE_MUTEX(syslog_lock); =20 +/* + * Specifies if a legacy console is registered. If legacy consoles are + * present, it is necessary to perform the console lock/unlock dance + * whenever console flushing should occur. + */ +static bool have_legacy_console; + /* * Specifies if a boot console is registered. If boot consoles are present, * nbcon consoles cannot print simultaneously and must be synchronized by @@ -471,6 +478,14 @@ static DEFINE_MUTEX(syslog_lock); */ bool have_boot_console; =20 +/* + * Specifies if the console lock/unlock dance is needed for console + * printing. If @have_boot_console is true, the nbcon consoles will + * be printed serially along with the legacy consoles because nbcon + * consoles cannot print simultaneously with boot consoles. + */ +#define printing_via_unlock (have_legacy_console || have_boot_console) + #ifdef CONFIG_PRINTK DECLARE_WAIT_QUEUE_HEAD(log_wait); /* All 3 protected by @syslog_lock. */ @@ -2339,7 +2354,7 @@ asmlinkage int vprintk_emit(int facility, int level, printed_len =3D vprintk_store(facility, level, dev_info, fmt, args); =20 /* If called from the scheduler, we can not call up(). */ - if (!in_sched) { + if (!in_sched && printing_via_unlock) { /* * The caller may be holding system-critical or * timing-sensitive locks. Disable preemption during @@ -2359,7 +2374,7 @@ asmlinkage int vprintk_emit(int facility, int level, preempt_enable(); } =20 - if (in_sched) + if (in_sched && printing_via_unlock) defer_console_output(); else wake_up_klogd(); @@ -2718,7 +2733,7 @@ void resume_console(void) */ static int console_cpu_notify(unsigned int cpu) { - if (!cpuhp_tasks_frozen) { + if (!cpuhp_tasks_frozen && printing_via_unlock) { /* If trylock fails, someone else is doing the printing */ if (console_trylock()) console_unlock(); @@ -3625,6 +3640,7 @@ void register_console(struct console *newcon) if (newcon->flags & CON_NBCON) { nbcon_seq_force(newcon, init_seq); } else { + have_legacy_console =3D true; newcon->seq =3D init_seq; } =20 @@ -3701,6 +3717,7 @@ EXPORT_SYMBOL(register_console); static int unregister_console_locked(struct console *console) { bool use_device_lock =3D (console->flags & CON_NBCON) && console->write_a= tomic; + bool found_legacy_con =3D false; bool found_boot_con =3D false; unsigned long flags; struct console *c; @@ -3768,9 +3785,13 @@ static int unregister_console_locked(struct console = *console) for_each_console(c) { if (c->flags & CON_BOOT) found_boot_con =3D true; + if (!(c->flags & CON_NBCON)) + found_legacy_con =3D true; } if (!found_boot_con) have_boot_console =3D found_boot_con; + if (!found_legacy_con) + have_legacy_console =3D found_legacy_con; =20 return res; } @@ -3931,8 +3952,10 @@ static bool __pr_flush(struct console *con, int time= out_ms, bool reset_on_progre seq =3D prb_next_reserve_seq(prb); =20 /* Flush the consoles so that records up to @seq are printed. */ - console_lock(); - console_unlock(); + if (printing_via_unlock) { + console_lock(); + console_unlock(); + } =20 for (;;) { unsigned long begin_jiffies; @@ -3945,6 +3968,12 @@ static bool __pr_flush(struct console *con, int time= out_ms, bool reset_on_progre * console->seq. Releasing console_lock flushes more * records in case @seq is still not printed on all * usable consoles. + * + * Holding the console_lock is not necessary if there + * are no legacy or boot consoles. However, such a + * console could register at any time. Always hold the + * console_lock as a precaution rather than + * synchronizing against register_console(). */ console_lock(); =20 --=20 2.39.2