linux-kernel - [PATCH printk v4 35/39] tty: serial: kgdboc: use console_list

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Message-Id: <20221114162932.141883-36-john.ogness@linutronix.de>
Date:   Mon, 14 Nov 2022 17:35:28 +0106
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 v4 35/39] tty: serial: kgdboc: use console_list_lock for list traversal

configure_kgdboc() uses the console_lock for console list iteration. Use
the console_list_lock instead because list synchronization responsibility
will be removed from the console_lock in a later change.

The SRCU iterator could have been used here, but a later change will
relocate the locking of the console_list_lock to also provide
synchronization against register_console().

Note, the console_lock is still needed to serialize the device()
callback with other console operations.

Signed-off-by: John Ogness <john.ogness@...utronix.de>
---
 drivers/tty/serial/kgdboc.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c
index c6df9ef34099..82b4b4d67823 100644
--- a/drivers/tty/serial/kgdboc.c
+++ b/drivers/tty/serial/kgdboc.c
@@ -193,7 +193,16 @@ static int configure_kgdboc(void)
 	if (!p)
 		goto noconfig;
 
+	/* For safe traversal of the console list. */
+	console_list_lock();
+
+	/*
+	 * 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(cons) {
 		int idx;
 		if (cons->device && cons->device(cons, &idx) == p &&
@@ -202,8 +211,11 @@ static int configure_kgdboc(void)
 			break;
 		}
 	}
+
 	console_unlock();
 
+	console_list_unlock();
+
 	kgdb_tty_driver = p;
 	kgdb_tty_line = tty_line;
 
-- 
2.30.2