linux-kernel - [PATCH printk v2 30/38] printk: console_device: use srcu console list iterator

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Message-Id: <20221019145600.1282823-31-john.ogness@linutronix.de>
Date:   Wed, 19 Oct 2022 17:01:52 +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
Subject: [PATCH printk v2 30/38] printk: console_device: use srcu console list iterator

Use srcu console list iteration for console list traversal.

Document why the console_lock is still necessary.

Signed-off-by: John Ogness <john.ogness@...utronix.de>
---
 kernel/printk/printk.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index e478cb92e7ba..410ad9d5649c 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3025,15 +3025,24 @@ struct tty_driver *console_device(int *index)
 {
 	struct console *c;
 	struct tty_driver *driver = NULL;
+	int cookie;
 
+	/*
+	 * Stop console printing because the device() callback may
+	 * assume the console is not within its write() callback.
+	 */
 	console_lock();
-	for_each_console(c) {
+
+	cookie = console_srcu_read_lock();
+	for_each_console_srcu(c) {
 		if (!c->device)
 			continue;
 		driver = c->device(c, index);
 		if (driver)
 			break;
 	}
+	console_srcu_read_unlock(cookie);
+
 	console_unlock();
 	return driver;
 }
-- 
2.30.2