Commit 3b604ca8 authored by John Ogness's avatar John Ogness Committed by Petr Mladek
Browse files

printk: add pr_flush() 



Provide a might-sleep function to allow waiting for console printers
to catch up to the latest logged message.

Use pr_flush() whenever it is desirable to get buffered messages
printed before continuing: suspend_console(), resume_console(),
console_stop(), console_start(), console_unblank().

Signed-off-by: default avatarJohn Ogness <john.ogness@linutronix.de>
Reviewed-by: default avatarPetr Mladek <pmladek@suse.com>
Signed-off-by: default avatarPetr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220421212250.565456-12-john.ogness@linutronix.de
parent 03a749e6

include/linux/printk.h

+7 −0
Original line number Diff line number Diff line
@@ -170,6 +170,8 @@ extern void __printk_safe_exit(void); 
#define printk_deferred_enter __printk_safe_enter

#define printk_deferred_exit __printk_safe_exit



extern bool pr_flush(int timeout_ms, bool reset_on_progress);



/*

 * Please don't use printk_ratelimit(), because it shares ratelimiting state

 * with all other unrelated printk_ratelimit() callsites.  Instead use
@@ -220,6 +222,11 @@ static inline void printk_deferred_exit(void) 
{

}



static inline bool pr_flush(int timeout_ms, bool reset_on_progress)

{

	return true;

}



static inline int printk_ratelimit(void)

{

	return 0;

kernel/printk/printk.c

+83 −0
Original line number Diff line number Diff line
@@ -2296,6 +2296,8 @@ asmlinkage __visible int _printk(const char *fmt, ...) 
}

EXPORT_SYMBOL(_printk);



static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress);



#else /* CONFIG_PRINTK */



#define CONSOLE_LOG_MAX		0
@@ -2328,6 +2330,7 @@ static void call_console_driver(struct console *con, const char *text, size_t le 
{

}

static bool suppress_message_printing(int level) { return false; }

static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress) { return true; }



#endif /* CONFIG_PRINTK */
@@ -2515,6 +2518,7 @@ void suspend_console(void) 
	if (!console_suspend_enabled)

		return;

	pr_info("Suspending console(s) (use no_console_suspend to debug)\n");

	pr_flush(1000, true);

	console_lock();

	console_suspended = 1;

	up_console_sem();
@@ -2527,6 +2531,7 @@ void resume_console(void) 
	down_console_sem();

	console_suspended = 0;

	console_unlock();

	pr_flush(1000, true);

}



/**
@@ -2912,6 +2917,9 @@ void console_unblank(void) 
		if ((c->flags & CON_ENABLED) && c->unblank)

			c->unblank();

	console_unlock();



	if (!oops_in_progress)

		pr_flush(1000, true);

}



/**
@@ -2970,6 +2978,7 @@ struct tty_driver *console_device(int *index) 
 */

void console_stop(struct console *console)

{

	__pr_flush(console, 1000, true);

	console_lock();

	console->flags &= ~CON_ENABLED;

	console_unlock();
@@ -2981,6 +2990,7 @@ void console_start(struct console *console) 
	console_lock();

	console->flags |= CON_ENABLED;

	console_unlock();

	__pr_flush(console, 1000, true);

}

EXPORT_SYMBOL(console_start);
@@ -3352,6 +3362,79 @@ static int __init printk_late_init(void) 
late_initcall(printk_late_init);



#if defined CONFIG_PRINTK

/* If @con is specified, only wait for that console. Otherwise wait for all. */

static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress)

{

	int remaining = timeout_ms;

	struct console *c;

	u64 last_diff = 0;

	u64 printk_seq;

	u64 diff;

	u64 seq;



	might_sleep();



	seq = prb_next_seq(prb);



	for (;;) {

		diff = 0;



		console_lock();

		for_each_console(c) {

			if (con && con != c)

				continue;

			if (!console_is_usable(c))

				continue;

			printk_seq = c->seq;

			if (printk_seq < seq)

				diff += seq - printk_seq;

		}

		console_unlock();



		if (diff != last_diff && reset_on_progress)

			remaining = timeout_ms;



		if (diff == 0 || remaining == 0)

			break;



		if (remaining < 0) {

			/* no timeout limit */

			msleep(100);

		} else if (remaining < 100) {

			msleep(remaining);

			remaining = 0;

		} else {

			msleep(100);

			remaining -= 100;

		}



		last_diff = diff;

	}



	return (diff == 0);

}



/**

 * pr_flush() - Wait for printing threads to catch up.

 *

 * @timeout_ms:        The maximum time (in ms) to wait.

 * @reset_on_progress: Reset the timeout if forward progress is seen.

 *

 * A value of 0 for @timeout_ms means no waiting will occur. A value of -1

 * represents infinite waiting.

 *

 * If @reset_on_progress is true, the timeout will be reset whenever any

 * printer has been seen to make some forward progress.

 *

 * Context: Process context. May sleep while acquiring console lock.

 * Return: true if all enabled printers are caught up.

 */

bool pr_flush(int timeout_ms, bool reset_on_progress)

{

	return __pr_flush(NULL, timeout_ms, reset_on_progress);

}

EXPORT_SYMBOL(pr_flush);



/*

 * Delayed printk version, for scheduler-internal messages:

 */