linux-kernel - [PATCH] printk: save loglevel before console

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Date: Thu, 15 Feb 2024 16:51:28 -0800
From: Stephen Brennan <stephen.s.brennan@...cle.com>
To: linux-kernel@...r.kernel.org
Cc: Petr Mladek <pmladek@...e.com>, Steven Rostedt <rostedt@...dmis.org>,
        John Ogness <john.ogness@...utronix.de>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Stephen Brennan <stephen.s.brennan@...cle.com>
Subject: [PATCH] printk: save loglevel before console_verbose()

In panic() cases, console_verbose() is called, clobbering the
console_loglevel value. If the bug which led to the panic related to
printk, it can be useful to know the log level prior to the
console_verbose() call. Save it to allow debugging these cases.

Signed-off-by: Stephen Brennan <stephen.s.brennan@...cle.com>
---
 kernel/printk/printk.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index f2444b581e16..97bd9427f118 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2521,11 +2521,19 @@ MODULE_PARM_DESC(console_suspend, "suspend console during suspend"
 	" and hibernate operations");
 
 static bool printk_console_no_auto_verbose;
+int saved_console_loglevel;
 
 void console_verbose(void)
 {
-	if (console_loglevel && !printk_console_no_auto_verbose)
+	if (console_loglevel && !printk_console_no_auto_verbose) {
+		/*
+		 * Save the prior log level for later debugging. Avoid
+		 * clobbering in case of multiple console_verbose() calls.
+		 */
+		if (console_loglevel != CONSOLE_LOGLEVEL_MOTORMOUTH)
+			saved_console_loglevel = console_loglevel;
 		console_loglevel = CONSOLE_LOGLEVEL_MOTORMOUTH;
+	}
 }
 EXPORT_SYMBOL_GPL(console_verbose);
 
-- 
2.39.3