linux-kernel - [PATCH printk v2 23/38] tty: tty_io: document console

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Message-Id: <20221019145600.1282823-24-john.ogness@linutronix.de>
Date:   Wed, 19 Oct 2022 17:01:45 +0206
From:   John Ogness <john.ogness@...utronix.de>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>
Subject: [PATCH printk v2 23/38] tty: tty_io: document console_lock usage

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@...utronix.de>
---
 drivers/tty/tty_io.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 2050e63963bb..333579bfa335 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -3526,6 +3526,14 @@ 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.
+	 *
+	 * Stop console printing because the device() callback may
+	 * assume the console is not within its write() callback.
+	 */
 	console_lock();
 	for_each_console(c) {
 		if (!c->device)
-- 
2.30.2