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

[Feng Tang]

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@xxxxxxxxx>
---
 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