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printk: add pr_flush()

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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: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220421212250.565456-12-john.ogness@linutronix.de
This commit is contained in:
John Ogness 2022-04-21 23:28:46 +02:06 committed by Petr Mladek
parent 03a749e628
commit 3b604ca812
2 changed files with 90 additions and 0 deletions
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7
include/linux/printk.h
View File

@ -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;

83
kernel/printk/printk.c
View File

@ -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:
*/