linux-kernel - [PATCH 2/2] panic: Enable to print out all printk msg in buffer

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Date:   Mon,  1 Apr 2019 18:48:04 +0800
From:   Feng Tang <feng.tang@...el.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        linux-kernel@...r.kernel.org
Cc:     Kees Cook <keescook@...omium.org>, Borislav Petkov <bp@...e.de>,
        Feng Tang <feng.tang@...el.com>
Subject: [PATCH 2/2] panic: Enable to print out all printk msg in buffer

Currently on panic, kernel will lower the loglevel and print out
new printk msg only. With this patch, user can configure the
"panic_print" to see all dmesg in buffer, some of which they may
have never seen due to the loglevel setting.

Signed-off-by: Feng Tang <feng.tang@...el.com>
---
 Documentation/admin-guide/kernel-parameters.txt | 1 +
 kernel/panic.c                                  | 9 ++++++++-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 2b8ee90..7b15c94 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3135,6 +3135,7 @@
 			bit 2: print timer info
 			bit 3: print locks info if CONFIG_LOCKDEP is on
 			bit 4: print ftrace buffer
+			bit 5: print all printk messages in buffer
 
 	panic_on_warn	panic() instead of WARN().  Useful to cause kdump
 			on a WARN().
diff --git a/kernel/panic.c b/kernel/panic.c
index fb77e01..afe023e 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -51,6 +51,7 @@ EXPORT_SYMBOL_GPL(panic_timeout);
 #define PANIC_PRINT_TIMER_INFO		0x00000004
 #define PANIC_PRINT_LOCK_INFO		0x00000008
 #define PANIC_PRINT_FTRACE_INFO		0x00000010
+#define PANIC_PRINT_ALL_PRINTK_MSG	0x00000020
 unsigned long panic_print;
 
 ATOMIC_NOTIFIER_HEAD(panic_notifier_list);
@@ -134,6 +135,13 @@ EXPORT_SYMBOL(nmi_panic);
 
 static void panic_print_sys_info(void)
 {
+	bool flush_all_dmesg = false;
+
+	if (panic_print & PANIC_PRINT_ALL_PRINTK_MSG)
+		flush_all_dmesg = true;
+
+	console_flush_on_panic(flush_all_dmesg);
+
 	if (panic_print & PANIC_PRINT_TASK_INFO)
 		show_state();
 
@@ -277,7 +285,6 @@ void panic(const char *fmt, ...)
 	 * panic() is not being callled from OOPS.
 	 */
 	debug_locks_off();
-	console_flush_on_panic(false);
 
 	panic_print_sys_info();
 
-- 
2.7.4