diff mbox series

[printk,v3,13/40] tty: tty_io: document console_lock usage

Message ID	20221107141638.3790965-14-john.ogness@linutronix.de
State	New
Headers	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; From: John Ogness <john.ogness@linutronix.de> 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, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Jiri Slaby <jirislaby@kernel.org> Subject: [PATCH printk v3 13/40] tty: tty_io: document console_lock usage Date: Mon, 7 Nov 2022 15:22:11 +0106 Message-Id: <20221107141638.3790965-14-john.ogness@linutronix.de> In-Reply-To: <20221107141638.3790965-1-john.ogness@linutronix.de> References: <20221107141638.3790965-1-john.ogness@linutronix.de> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk
Series	reduce console_lock scope \| [printk,v3,00/40] reduce console_lock scope [printk,v3,01/40] rcu: implement lockdep_rcu_enabled for !CONFIG_DEBUG_LOCK_ALLOC [printk,v3,02/40] serial: kgdboc: Lock console list in probe function [printk,v3,03/40] printk: Convert console_drivers list to hlist [printk,v3,04/40] printk: Prepare for SRCU console list protection [printk,v3,05/40] printk: fix setting first seq for consoles [printk,v3,06/40] um: kmsg_dump: only dump when no output console available [printk,v3,07/40] console: introduce console_is_enabled() wrapper [printk,v3,08/40] printk: use console_is_enabled() [printk,v3,09/40] um: kmsg_dump: use console_is_enabled() [printk,v3,10/40] kdb: kdb_io: use console_is_enabled() [printk,v3,11/40] um: kmsg_dumper: use srcu console list iterator [printk,v3,12/40] tty: serial: kgdboc: document console_lock usage [printk,v3,13/40] tty: tty_io: document console_lock usage [printk,v3,14/40] proc: consoles: document console_lock usage [printk,v3,15/40] kdb: use srcu console list iterator [printk,v3,16/40] printk: console_flush_all: use srcu console list iterator [printk,v3,17/40] printk: console_unblank: use srcu console list iterator [printk,v3,18/40] printk: console_flush_on_panic: use srcu console list iterator [printk,v3,19/40] printk: console_device: use srcu console list iterator [printk,v3,20/40] printk: __pr_flush: use srcu console list iterator [printk,v3,21/40] printk: introduce console_list_lock [printk,v3,22/40] console: introduce console_is_registered() [printk,v3,23/40] serial_core: replace uart_console_enabled() with uart_console_registered() [printk,v3,24/40] tty: nfcon: use console_is_registered() [printk,v3,25/40] efi: earlycon: use console_is_registered() [printk,v3,26/40] tty: hvc: use console_is_registered() [printk,v3,27/40] tty: serial: earlycon: use console_is_registered() [printk,v3,28/40] tty: serial: pic32_uart: use console_is_registered() [printk,v3,29/40] tty: serial: samsung_tty: use console_is_registered() [printk,v3,30/40] tty: serial: xilinx_uartps: use console_is_registered() [printk,v3,31/40] usb: early: xhci-dbc: use console_is_registered() [printk,v3,32/40] netconsole: avoid CON_ENABLED misuse to track registration [printk,v3,33/40] printk, xen: fbfront: create/use safe function for forcing preferred [printk,v3,34/40] tty: tty_io: use console_list_lock for list synchronization [printk,v3,35/40] proc: consoles: use console_list_lock for list iteration [printk,v3,36/40] tty: serial: kgdboc: use console_list_lock for list traversal [printk,v3,37/40] tty: serial: kgdboc: synchronize tty_find_polling_driver() and register_console() [printk,v3,38/40] tty: serial: kgdboc: use console_list_lock to trap exit [printk,v3,39/40] printk: relieve console_lock of list synchronization duties [printk,v3,40/40] tty: serial: sh-sci: use setup() callback for early console

Commit Message

John Ogness Nov. 7, 2022, 2:16 p.m. UTC

  show_cons_active() uses the console_lock to gather information
on registered consoles. Since the console_lock is being used for
multiple reasons, explicitly document these reasons. This will
be useful when the console_lock is split into fine-grained
locking.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
 drivers/tty/tty_io.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

Comments

Petr Mladek Nov. 9, 2022, 3:20 p.m. UTC | #1

On Mon 2022-11-07 15:22:11, John Ogness wrote:
> show_cons_active() uses the console_lock to gather information
> on registered consoles. Since the console_lock is being used for
> multiple reasons, explicitly document these reasons. This will
> be useful when the console_lock is split into fine-grained
> locking.

It is great to have this documented.

> Signed-off-by: John Ogness <john.ogness@linutronix.de>

Reviewed-by: Petr Mladek <pmladek@suse.com>

Best Regards,
Petr

diff mbox series

Patch

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index de06c3c2ff70..ee4da2fec328 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -3526,6 +3526,16 @@  static ssize_t show_cons_active(struct device *dev,
 	struct console *c;
 	ssize_t count = 0;
 
+	/*
+	 * Hold the console_lock to guarantee that no consoles are
+	 * unregistered until all console processing is complete.
+	 * This also allows safe traversal of the console list and
+	 * race-free reading of @flags.
+	 *
+	 * Take console_lock to serialize device() callback with
+	 * other console operations. For example, fg_console is
+	 * modified under console_lock when switching vt.
+	 */
 	console_lock();
 	for_each_console(c) {
 		if (!c->device)