linux-kernel - [PATCH printk v3 14/14] panic: Flush kernel log buffer at the end

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Message-Id: <20231214214201.499426-15-john.ogness@linutronix.de>
Date: Thu, 14 Dec 2023 22:48:01 +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,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	"Guilherme G. Piccoli" <gpiccoli@...lia.com>,
	Kefeng Wang <wangkefeng.wang@...wei.com>,
	Kees Cook <keescook@...omium.org>,
	Uros Bizjak <ubizjak@...il.com>,
	Arnd Bergmann <arnd@...db.de>
Subject: [PATCH printk v3 14/14] panic: Flush kernel log buffer at the end

If the kernel crashes in a context where printk() calls always
defer printing (such as in NMI or inside a printk_safe section)
then the final panic messages will be deferred to irq_work. But
if irq_work is not available, the messages will not get printed
unless explicitly flushed. The result is that the final
"end Kernel panic" banner does not get printed.

Add one final flush after the last printk() call to make sure
the final panic messages make it out as well.

Signed-off-by: John Ogness <john.ogness@...utronix.de>
---
 kernel/panic.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/panic.c b/kernel/panic.c
index 2807639aab51..f22d8f33ea14 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -446,6 +446,14 @@ void panic(const char *fmt, ...)
 
 	/* Do not scroll important messages printed above */
 	suppress_printk = 1;
+
+	/*
+	 * The final messages may not have been printed if in a context that
+	 * defers printing (such as NMI) and irq_work is not available.
+	 * Explicitly flush the kernel log buffer one last time.
+	 */
+	console_flush_on_panic(CONSOLE_FLUSH_PENDING);
+
 	local_irq_enable();
 	for (i = 0; ; i += PANIC_TIMER_STEP) {
 		touch_softlockup_watchdog();
-- 
2.39.2