panic: add an option to replay all the printk message in buffer

Currently on panic, kernel will lower the loglevel and print out pending
printk msg only with console_flush_on_panic().

Add an option for users to configure the "panic_print" to replay all dmesg
in buffer, some of which they may have never seen due to the loglevel
setting, which will help panic debugging .

Link: http://lkml.kernel.org/r/1556095872-36838-1-git-send-email-feng.tang@intel.com
Signed-off-by: Feng Tang <feng.tang@intel.com>
Cc: Aaro Koskinen <aaro.koskinen@nokia.com>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Borislav Petkov <bp@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>

5 files changed, 21 insertions, 5 deletions

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 5e73c16c8f54..4fa795813b8b 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3145,6 +3145,7 @@
 			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/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 1fd45a8650e1..0fb785ed5ec6 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -179,7 +179,7 @@ extern void panic_flush_kmsg_end(void)
 	kmsg_dump(KMSG_DUMP_PANIC);
 	bust_spinlocks(0);
 	debug_locks_off();
-	console_flush_on_panic();
+	console_flush_on_panic(CONSOLE_FLUSH_PENDING);
 }
 
 static unsigned long oops_begin(struct pt_regs *regs)
diff --git a/include/linux/console.h b/include/linux/console.h
index ec9bdb3d7bab..d09951d5a94e 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -166,6 +166,11 @@ struct console {
 extern int console_set_on_cmdline;
 extern struct console *early_console;
 
+enum con_flush_mode {
+	CONSOLE_FLUSH_PENDING,
+	CONSOLE_REPLAY_ALL,
+};
+
 extern int add_preferred_console(char *name, int idx, char *options);
 extern void register_console(struct console *);
 extern int unregister_console(struct console *);
@@ -175,7 +180,7 @@ extern int console_trylock(void);
 extern void console_unlock(void);
 extern void console_conditional_schedule(void);
 extern void console_unblank(void);
-extern void console_flush_on_panic(void);
+extern void console_flush_on_panic(enum con_flush_mode mode);
 extern struct tty_driver *console_device(int *);
 extern void console_stop(struct console *);
 extern void console_start(struct console *);
diff --git a/kernel/panic.c b/kernel/panic.c
index cd73af35ec66..eacd9dd10a41 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 +135,11 @@ EXPORT_SYMBOL(nmi_panic);
 
 static void panic_print_sys_info(void)
 {
+	if (panic_print & PANIC_PRINT_ALL_PRINTK_MSG)
+		console_flush_on_panic(CONSOLE_REPLAY_ALL);
+	else
+		console_flush_on_panic(CONSOLE_FLUSH_PENDING);
+
 	if (panic_print & PANIC_PRINT_TASK_INFO)
 		show_state();
 
@@ -277,8 +283,6 @@ void panic(const char *fmt, ...)
 	 * panic() is not being callled from OOPS.
 	 */
 	debug_locks_off();
-	console_flush_on_panic();
-
 	panic_print_sys_info();
 
 	if (!panic_blink)
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 17102fd4c136..e1e82506b2dd 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2535,10 +2535,11 @@ void console_unblank(void)
 
 /**
  * console_flush_on_panic - flush console content on panic
+ * @mode: flush all messages in buffer or just the pending ones
  *
  * Immediately output all pending messages no matter what.
  */
-void console_flush_on_panic(void)
+void console_flush_on_panic(enum con_flush_mode mode)
 {
 	/*
 	 * If someone else is holding the console lock, trylock will fail
@@ -2549,6 +2550,11 @@ void console_flush_on_panic(void)
 	 */
 	console_trylock();
 	console_may_schedule = 0;
+
+	if (mode == CONSOLE_REPLAY_ALL) {
+		console_seq = log_first_seq;
+		console_idx = log_first_idx;
+	}
 	console_unlock();
 }