linux-kernel - [PATCH v2 2/2] tty: sysrq: Use printk_force_console context on __handle

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Message-Id: <20241105-printk-loud-con-v2-2-bd3ecdf7b0e4@suse.com>
Date: Tue, 05 Nov 2024 16:45:09 -0300
From: Marcos Paulo de Souza <mpdesouza@...e.com>
To: Petr Mladek <pmladek@...e.com>, Steven Rostedt <rostedt@...dmis.org>, 
 John Ogness <john.ogness@...utronix.de>, 
 Sergey Senozhatsky <senozhatsky@...omium.org>, 
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
 Jiri Slaby <jirislaby@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org, 
 Marcos Paulo de Souza <mpdesouza@...e.com>
Subject: [PATCH v2 2/2] tty: sysrq: Use printk_force_console context on
 __handle_sysrq

By using the printk_force_console the loglevel workaround can be removed.
The workaround existed to always send the sysrq header message to all
consoles not matter what was the current loglevel, but it won't work for
deferred messages, since the loglevel can be restore before the message
is printed, suppressing the message that wasn't supposed to be
suppressed by the workaround.

Signed-off-by: Marcos Paulo de Souza <mpdesouza@...e.com>
---
 drivers/tty/sysrq.c | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index 930b04e3d148..f85ce02e4725 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -583,7 +583,6 @@ static void __sysrq_put_key_op(u8 key, const struct sysrq_key_op *op_p)
 void __handle_sysrq(u8 key, bool check_mask)
 {
 	const struct sysrq_key_op *op_p;
-	int orig_log_level;
 	int orig_suppress_printk;
 	int i;
 
@@ -593,13 +592,12 @@ void __handle_sysrq(u8 key, bool check_mask)
 	rcu_sysrq_start();
 	rcu_read_lock();
 	/*
-	 * Raise the apparent loglevel to maximum so that the sysrq header
-	 * is shown to provide the user with positive feedback.  We do not
-	 * simply emit this at KERN_EMERG as that would change message
-	 * routing in the consumers of /proc/kmsg.
+	 * Enter in the force_console context so that sysrq header is shown to
+	 * provide the user with positive feedback.  We do not simply emit this
+	 * at KERN_EMERG as that would change message routing in the consumers
+	 * of /proc/kmsg.
 	 */
-	orig_log_level = console_loglevel;
-	console_loglevel = CONSOLE_LOGLEVEL_DEFAULT;
+	printk_force_console_enter();
 
 	op_p = __sysrq_get_key_op(key);
 	if (op_p) {
@@ -609,11 +607,11 @@ void __handle_sysrq(u8 key, bool check_mask)
 		 */
 		if (!check_mask || sysrq_on_mask(op_p->enable_mask)) {
 			pr_info("%s\n", op_p->action_msg);
-			console_loglevel = orig_log_level;
+			printk_force_console_exit();
 			op_p->handler(key);
 		} else {
 			pr_info("This sysrq operation is disabled.\n");
-			console_loglevel = orig_log_level;
+			printk_force_console_exit();
 		}
 	} else {
 		pr_info("HELP : ");
@@ -631,7 +629,7 @@ void __handle_sysrq(u8 key, bool check_mask)
 			}
 		}
 		pr_cont("\n");
-		console_loglevel = orig_log_level;
+		printk_force_console_exit();
 	}
 	rcu_read_unlock();
 	rcu_sysrq_end();

-- 
2.47.0