linux-kernel - [PATCH printk v3 35/40] proc: consoles: use console_list

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Date:   Mon,  7 Nov 2022 15:22:33 +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,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-fsdevel@...r.kernel.org
Subject: [PATCH printk v3 35/40] proc: consoles: use console_list_lock for list iteration

The console_lock is used in part to guarantee safe list iteration.
The console_list_lock should be used because list synchronization
responsibility will be removed from the console_lock in a later
change.

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>
Reviewed-by: Petr Mladek <pmladek@...e.com>
---
 fs/proc/consoles.c | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/fs/proc/consoles.c b/fs/proc/consoles.c
index 46b305fa04ed..e0758fe7936d 100644
--- a/fs/proc/consoles.c
+++ b/fs/proc/consoles.c
@@ -33,7 +33,16 @@ static int show_console_dev(struct seq_file *m, void *v)
 	if (con->device) {
 		const struct tty_driver *driver;
 		int index;
+
+		/*
+		 * 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();
 		driver = con->device(con, &index);
+		console_unlock();
+
 		if (driver) {
 			dev = MKDEV(driver->major, driver->minor_start);
 			dev += index;
@@ -64,15 +73,11 @@ static void *c_start(struct seq_file *m, loff_t *pos)
 	loff_t off = 0;
 
 	/*
-	 * Take console_lock to serialize device() callback with
-	 * other console operations. For example, fg_console is
-	 * modified under console_lock when switching vt.
-	 *
-	 * Hold the console_lock to guarantee safe traversal of the
+	 * Hold the console_list_lock to guarantee safe traversal of the
 	 * console list. SRCU cannot be used because there is no
 	 * place to store the SRCU cookie.
 	 */
-	console_lock();
+	console_list_lock();
 	for_each_console(con)
 		if (off++ == *pos)
 			break;
@@ -90,7 +95,7 @@ static void *c_next(struct seq_file *m, void *v, loff_t *pos)
 
 static void c_stop(struct seq_file *m, void *v)
 {
-	console_unlock();
+	console_list_unlock();
 }
 
 static const struct seq_operations consoles_op = {
-- 
2.30.2