Commit 693f75b9 authored by Sreenath Vijayan's avatar Sreenath Vijayan Committed by Greg Kroah-Hartman
Browse files

printk: Add function to replay kernel log on consoles 



Add a generic function console_replay_all() for replaying
the kernel log on consoles, in any context. It would allow
viewing the logs on an unresponsive terminal via sysrq.

Reuse the existing code from console_flush_on_panic() for
resetting the sequence numbers, by introducing a new helper
function __console_rewind_all(). It is safe to be called
under console_lock().

Try to acquire lock on the console subsystem without waiting.
If successful, reset the sequence number to oldest available
record on all consoles and call console_unlock() which will
automatically flush the messages to the consoles.

Suggested-by: default avatarJohn Ogness <john.ogness@linutronix.de>
Suggested-by: default avatarPetr Mladek <pmladek@suse.com>
Signed-off-by: default avatarShimoyashiki Taichi <taichi.shimoyashiki@sony.com>
Reviewed-by: default avatarJohn Ogness <john.ogness@linutronix.de>
Signed-off-by: default avatarSreenath Vijayan <sreenath.vijayan@sony.com>
Link: https://lore.kernel.org/r/90ee131c643a5033d117b556c0792de65129d4c3.1710220326.git.sreenath.vijayan@sony.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 25ca2d57

include/linux/printk.h

+4 −0
Original line number Diff line number Diff line
@@ -195,6 +195,7 @@ void show_regs_print_info(const char *log_lvl); 
extern asmlinkage void dump_stack_lvl(const char *log_lvl) __cold;

extern asmlinkage void dump_stack(void) __cold;

void printk_trigger_flush(void);

void console_replay_all(void);

#else

static inline __printf(1, 0)

int vprintk(const char *s, va_list args)
@@ -274,6 +275,9 @@ static inline void dump_stack(void) 
static inline void printk_trigger_flush(void)

{

}

static inline void console_replay_all(void)

{

}

#endif



bool this_cpu_in_panic(void);

kernel/printk/printk.c

+53 −24
Original line number Diff line number Diff line
@@ -3161,6 +3161,40 @@ void console_unblank(void) 
		pr_flush(1000, true);

}



/*

 * Rewind all consoles to the oldest available record.

 *

 * IMPORTANT: The function is safe only when called under

 *            console_lock(). It is not enforced because

 *            it is used as a best effort in panic().

 */

static void __console_rewind_all(void)

{

	struct console *c;

	short flags;

	int cookie;

	u64 seq;



	seq = prb_first_valid_seq(prb);



	cookie = console_srcu_read_lock();

	for_each_console_srcu(c) {

		flags = console_srcu_read_flags(c);



		if (flags & CON_NBCON) {

			nbcon_seq_force(c, seq);

		} else {

			/*

			 * This assignment is safe only when called under

			 * console_lock(). On panic, legacy consoles are

			 * only best effort.

			 */

			c->seq = seq;

		}

	}

	console_srcu_read_unlock(cookie);

}



/**

 * console_flush_on_panic - flush console content on panic

 * @mode: flush all messages in buffer or just the pending ones
@@ -3189,30 +3223,8 @@ void console_flush_on_panic(enum con_flush_mode mode) 
	 */

	console_may_schedule = 0;



	if (mode == CONSOLE_REPLAY_ALL) {

		struct console *c;

		short flags;

		int cookie;

		u64 seq;



		seq = prb_first_valid_seq(prb);



		cookie = console_srcu_read_lock();

		for_each_console_srcu(c) {

			flags = console_srcu_read_flags(c);



			if (flags & CON_NBCON) {

				nbcon_seq_force(c, seq);

			} else {

				/*

				 * This is an unsynchronized assignment. On

				 * panic legacy consoles are only best effort.

				 */

				c->seq = seq;

			}

		}

		console_srcu_read_unlock(cookie);

	}

	if (mode == CONSOLE_REPLAY_ALL)

		__console_rewind_all();



	console_flush_all(false, &next_seq, &handover);

}
@@ -4301,6 +4313,23 @@ void kmsg_dump_rewind(struct kmsg_dump_iter *iter) 
}

EXPORT_SYMBOL_GPL(kmsg_dump_rewind);



/**

 * console_replay_all - replay kernel log on consoles

 *

 * Try to obtain lock on console subsystem and replay all

 * available records in printk buffer on the consoles.

 * Does nothing if lock is not obtained.

 *

 * Context: Any context.

 */

void console_replay_all(void)

{

	if (console_trylock()) {

		__console_rewind_all();

		/* Consoles are flushed as part of console_unlock(). */

		console_unlock();

	}

}

#endif



#ifdef CONFIG_SMP