linux-kernel - [PATCH printk v2 22/38] serial: kgdboc: document console

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Message-Id: <20221019145600.1282823-23-john.ogness@linutronix.de>
Date:   Wed, 19 Oct 2022 17:01:44 +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,
        Jason Wessel <jason.wessel@...driver.com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Douglas Anderson <dianders@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        kgdb-bugreport@...ts.sourceforge.net, linux-serial@...r.kernel.org
Subject: [PATCH printk v2 22/38] serial: kgdboc: document console_lock usage

kgdboc_earlycon_init() uses the console_lock to ensure that no consoles
are unregistered until the kgdboc_earlycon is setup. This is necessary
because the trapping of the exit() callback assumes that the exit()
callback is not called before the trap is setup.

Explicitly document this non-typical console_lock usage.

Signed-off-by: John Ogness <john.ogness@...utronix.de>
---
 drivers/tty/serial/kgdboc.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c
index e9d3f8c6e3dc..48000666789a 100644
--- a/drivers/tty/serial/kgdboc.c
+++ b/drivers/tty/serial/kgdboc.c
@@ -545,6 +545,14 @@ static int __init kgdboc_earlycon_init(char *opt)
 	 * Look for a matching console, or if the name was left blank just
 	 * pick the first one we find.
 	 */
+
+	/*
+	 * Hold the console_lock to guarantee that no consoles are
+	 * unregistered until the kgdboc_earlycon setup is complete.
+	 * Trapping the exit() callback relies on exit() not being
+	 * called until the trap is setup. This also allows safe
+	 * traversal of the console list.
+	 */
 	console_lock();
 	for_each_console(con) {
 		if (con->write && con->read &&
-- 
2.30.2