Commit 741ea7aa authored by Andrew Murray's avatar Andrew Murray Committed by Petr Mladek
Browse files

printk: Introduce console_flush_one_record 



console_flush_all prints all remaining records to all usable consoles
whilst its caller holds console_lock. This can result in large waiting
times for those waiting for console_lock especially where there is a
large volume of records or where the console is slow (e.g. serial).

Let's extract the parts of this function which print a single record
into a new function named console_flush_one_record. This can later
be used for functions that will release and reacquire console_lock
between records.

This commit should not change existing functionality.

Reviewed-by: default avatarPetr Mladek <pmladek@suse.com>
Signed-off-by: default avatarAndrew Murray <amurray@thegoodpenguin.co.uk>
Reviewed-by: default avatarJohn Ogness <john.ogness@linutronix.de>
Link: https://patch.msgid.link/20251020-printk_legacy_thread_console_lock-v3-1-00f1f0ac055a@thegoodpenguin.co.uk


Signed-off-by: default avatarPetr Mladek <pmladek@suse.com>
parent 48e3694a

kernel/printk/printk.c

+99 −59
Original line number Diff line number Diff line
@@ -3134,43 +3134,39 @@ static inline void printk_kthreads_check_locked(void) { } 


#endif /* CONFIG_PRINTK */





/*

 * Print out all remaining records to all consoles.

 * Print out one record for each console.

 *

 * @do_cond_resched is set by the caller. It can be true only in schedulable

 * context.

 *

 * @next_seq is set to the sequence number after the last available record.

 * The value is valid only when this function returns true. It means that all

 * usable consoles are completely flushed.

 * The value is valid only when there is at least one usable console and all

 * usable consoles were flushed.

 *

 * @handover will be set to true if a printk waiter has taken over the

 * console_lock, in which case the caller is no longer holding the

 * console_lock. Otherwise it is set to false.

 *

 * Returns true when there was at least one usable console and all messages

 * were flushed to all usable consoles. A returned false informs the caller

 * that everything was not flushed (either there were no usable consoles or

 * another context has taken over printing or it is a panic situation and this

 * is not the panic CPU). Regardless the reason, the caller should assume it

 * is not useful to immediately try again.

 * @any_usable will be set to true if there are any usable consoles.

 *

 * Returns true when there was at least one usable console and a record was

 * flushed. A returned false indicates there were no records to flush for any

 * of the consoles. It may also indicate that there were no usable consoles,

 * the context has been lost or there is a panic suitation. Regardless the

 * reason, the caller should assume it is not useful to immediately try again.

 *

 * Requires the console_lock.

 */

static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handover)

static bool console_flush_one_record(bool do_cond_resched, u64 *next_seq, bool *handover,

				     bool *any_usable)

{

	struct console_flush_type ft;

	bool any_usable = false;

	bool any_progress = false;

	struct console *con;

	bool any_progress;

	int cookie;



	*next_seq = 0;

	*handover = false;



	do {

		any_progress = false;



	printk_get_console_flush_type(&ft);



	cookie = console_srcu_read_lock();
@@ -3180,8 +3176,8 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove 
		bool progress;



		/*

			 * console_flush_all() is only responsible for nbcon

			 * consoles when the nbcon consoles cannot print via

		 * console_flush_one_record() is only responsible for

		 * nbcon consoles when the nbcon consoles cannot print via

		 * their atomic or threaded flushing.

		 */

		if ((flags & CON_NBCON) && (ft.nbcon_atomic || ft.nbcon_offload))
@@ -3189,7 +3185,7 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove 


		if (!console_is_usable(con, flags, !do_cond_resched))

			continue;

			any_usable = true;

		*any_usable = true;



		if (flags & CON_NBCON) {

			progress = nbcon_legacy_emit_next_record(con, handover, cookie,
@@ -3223,15 +3219,59 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove 
			cond_resched();

	}

	console_srcu_read_unlock(cookie);

	} while (any_progress);



	return any_usable;

	return any_progress;



abandon:

	console_srcu_read_unlock(cookie);

	return false;

}



/*

 * Print out all remaining records to all consoles.

 *

 * @do_cond_resched is set by the caller. It can be true only in schedulable

 * context.

 *

 * @next_seq is set to the sequence number after the last available record.

 * The value is valid only when this function returns true. It means that all

 * usable consoles are completely flushed.

 *

 * @handover will be set to true if a printk waiter has taken over the

 * console_lock, in which case the caller is no longer holding the

 * console_lock. Otherwise it is set to false.

 *

 * Returns true when there was at least one usable console and all messages

 * were flushed to all usable consoles. A returned false informs the caller

 * that everything was not flushed (either there were no usable consoles or

 * another context has taken over printing or it is a panic situation and this

 * is not the panic CPU). Regardless the reason, the caller should assume it

 * is not useful to immediately try again.

 *

 * Requires the console_lock.

 */

static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handover)

{

	bool any_usable = false;

	bool any_progress;



	*next_seq = 0;

	*handover = false;



	do {

		any_progress = console_flush_one_record(do_cond_resched, next_seq, handover,

							&any_usable);



		if (*handover)

			return false;



		if (panic_on_other_cpu())

			return false;

	} while (any_progress);



	return any_usable;

}



static void __console_flush_and_unlock(void)

{

	bool do_cond_resched;