Commit 9e70a5e1 authored by John Ogness's avatar John Ogness Committed by Petr Mladek
Browse files

printk: Add per-console suspended state 



Currently the global @console_suspended is used to determine if
consoles are in a suspended state. Its primary purpose is to allow
usage of the console_lock when suspended without causing console
printing. It is synchronized by the console_lock.

Rather than relying on the console_lock to determine suspended
state, make it an official per-console state that is set within
console->flags. This allows the state to be queried via SRCU.

Remove @console_suspended. Console printing will still be avoided
when suspended because console_is_usable() returns false when
the new suspended flag is set for that console.

Signed-off-by: default avatarJohn Ogness <john.ogness@linutronix.de>
Reviewed-by: default avatarSergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: default avatarPetr Mladek <pmladek@suse.com>
Signed-off-by: default avatarPetr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20230717194607.145135-7-john.ogness@linutronix.de
parent 696ffaf5

include/linux/console.h

+3 −0
Original line number Diff line number Diff line
@@ -154,6 +154,8 @@ static inline int con_debug_leave(void) 
 *			receiving the printk spam for obvious reasons.

 * @CON_EXTENDED:	The console supports the extended output format of

 *			/dev/kmesg which requires a larger output buffer.

 * @CON_SUSPENDED:	Indicates if a console is suspended. If true, the

 *			printing callbacks must not be called.

 */

enum cons_flags {

	CON_PRINTBUFFER		= BIT(0),
@@ -163,6 +165,7 @@ enum cons_flags { 
	CON_ANYTIME		= BIT(4),

	CON_BRL			= BIT(5),

	CON_EXTENDED		= BIT(6),

	CON_SUSPENDED		= BIT(7),

};



/**

kernel/printk/printk.c

+44 −30
Original line number Diff line number Diff line
@@ -86,7 +86,7 @@ EXPORT_SYMBOL(oops_in_progress); 
static DEFINE_MUTEX(console_mutex);



/*

 * console_sem protects updates to console->seq and console_suspended,

 * console_sem protects updates to console->seq

 * and also provides serialization for console printing.

 */

static DEFINE_SEMAPHORE(console_sem);
@@ -359,7 +359,7 @@ static bool panic_in_progress(void) 
 * paths in the console code where we end up in places I want

 * locked without the console semaphore held).

 */

static int console_locked, console_suspended;

static int console_locked;



/*

 *	Array of consoles built from command line options (console=)
@@ -2549,22 +2549,46 @@ MODULE_PARM_DESC(console_no_auto_verbose, "Disable console loglevel raise to hig 
 */

void suspend_console(void)

{

	struct console *con;



	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();



	console_list_lock();

	for_each_console(con)

		console_srcu_write_flags(con, con->flags | CON_SUSPENDED);

	console_list_unlock();



	/*

	 * Ensure that all SRCU list walks have completed. All printing

	 * contexts must be able to see that they are suspended so that it

	 * is guaranteed that all printing has stopped when this function

	 * completes.

	 */

	synchronize_srcu(&console_srcu);

}



void resume_console(void)

{

	struct console *con;



	if (!console_suspend_enabled)

		return;

	down_console_sem();

	console_suspended = 0;

	console_unlock();



	console_list_lock();

	for_each_console(con)

		console_srcu_write_flags(con, con->flags & ~CON_SUSPENDED);

	console_list_unlock();



	/*

	 * Ensure that all SRCU list walks have completed. All printing

	 * contexts must be able to see they are no longer suspended so

	 * that they are guaranteed to wake up and resume printing.

	 */

	synchronize_srcu(&console_srcu);



	pr_flush(1000, true);

}
@@ -2623,8 +2647,6 @@ void console_lock(void) 
		msleep(1000);



	down_console_sem();

	if (console_suspended)

		return;

	console_locked = 1;

	console_may_schedule = 1;

}
@@ -2645,10 +2667,6 @@ int console_trylock(void) 
		return 0;

	if (down_trylock_console_sem())

		return 0;

	if (console_suspended) {

		up_console_sem();

		return 0;

	}

	console_locked = 1;

	console_may_schedule = 0;

	return 1;
@@ -2674,6 +2692,9 @@ static inline bool console_is_usable(struct console *con) 
	if (!(flags & CON_ENABLED))

		return false;



	if ((flags & CON_SUSPENDED))

		return false;



	if (!con->write)

		return false;
@@ -2992,11 +3013,6 @@ void console_unlock(void) 
	bool flushed;

	u64 next_seq;



	if (console_suspended) {

		up_console_sem();

		return;

	}



	/*

	 * Console drivers are called with interrupts disabled, so

	 * @console_may_schedule should be cleared before; however, we may
@@ -3726,8 +3742,7 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre 


		/*

		 * Hold the console_lock to guarantee safe access to

		 * console->seq and to prevent changes to @console_suspended

		 * until all consoles have been processed.

		 * console->seq.

		 */

		console_lock();
@@ -3735,6 +3750,11 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre 
		for_each_console_srcu(c) {

			if (con && con != c)

				continue;

			/*

			 * If consoles are not usable, it cannot be expected

			 * that they make forward progress, so only increment

			 * @diff for usable consoles.

			 */

			if (!console_is_usable(c))

				continue;

			printk_seq = c->seq;
@@ -3743,18 +3763,12 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre 
		}

		console_srcu_read_unlock(cookie);



		/*

		 * If consoles are suspended, it cannot be expected that they

		 * make forward progress, so timeout immediately. @diff is

		 * still used to return a valid flush status.

		 */

		if (console_suspended)

			remaining = 0;

		else if (diff != last_diff && reset_on_progress)

		if (diff != last_diff && reset_on_progress)

			remaining = timeout_ms;



		console_unlock();



		/* Note: @diff is 0 if there are no usable consoles. */

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

			break;
@@ -3788,7 +3802,7 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre 
 * 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.

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

 */

static bool pr_flush(int timeout_ms, bool reset_on_progress)

{