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Subject[PATCH v4] panic: add an option to replay all the printk message in buffer
Date
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 .

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>
---
Changelog:

v4:
- keep the original console_flush_on_panic() inside
panic(), as suggested by Petr Mladek

v3:
- Solve the compile issue when CONFIG_PRINTK=n, found by
Andrew Morton
- Add enum for parameter of console_flush_on_panic()
- move the printk replay code to console_flush_on_panic()

v2:
- Add a new func in printk.c dedicated for the replaying, as
suggested by Petr Mladek
- Combine the 2 patches in v1 into one suggested by both Petr
and Sergey

Documentation/admin-guide/kernel-parameters.txt | 1 +
arch/powerpc/kernel/traps.c | 2 +-
include/linux/console.h | 7 ++++++-
kernel/panic.c | 6 +++++-
kernel/printk/printk.c | 8 +++++++-
5 files changed, 20 insertions(+), 4 deletions(-)

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/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 1fd45a8..0fb785e 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 ec9bdb3..d09951d 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 0ae0d73..f795feb 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 +135,9 @@ 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);
+
if (panic_print & PANIC_PRINT_TASK_INFO)
show_state();

@@ -277,7 +281,7 @@ void panic(const char *fmt, ...)
* panic() is not being callled from OOPS.
*/
debug_locks_off();
- console_flush_on_panic();
+ console_flush_on_panic(CONSOLE_FLUSH_PENDING);

panic_print_sys_info();

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 02ca827..54f93de 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2525,10 +2525,11 @@ 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
@@ -2539,6 +2540,11 @@ 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();
}

--
2.7.4
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