Commit 26873e3e authored by John Ogness's avatar John Ogness Committed by Petr Mladek
Browse files

printk: Avoid scheduling irq_work on suspend 

Allowing irq_work to be scheduled while trying to suspend has shown
to cause problems as some architectures interpret the pending
interrupts as a reason to not suspend. This became a problem for
printk() with the introduction of NBCON consoles. With every
printk() call, NBCON console printing kthreads are woken by queueing
irq_work. This means that irq_work continues to be queued due to
printk() calls late in the suspend procedure.

Avoid this problem by preventing printk() from queueing irq_work
once console suspending has begun. This applies to triggering NBCON
and legacy deferred printing as well as klogd waiters.

Since triggering of NBCON threaded printing relies on irq_work, the
pr_flush() within console_suspend_all() is used to perform the final
flushing before suspending consoles and blocking irq_work queueing.
NBCON consoles that are not suspended (due to the usage of the
"no_console_suspend" boot argument) transition to atomic flushing.

Introduce a new global variable @console_irqwork_blocked to flag
when irq_work queueing is to be avoided. The flag is used by
printk_get_console_flush_type() to avoid allowing deferred printing
and switch NBCON consoles to atomic flushing. It is also used by
vprintk_emit() to avoid klogd waking.

Add WARN_ON_ONCE(console_irqwork_blocked) to the irq_work queuing
functions to catch any code that attempts to queue printk irq_work
during the suspending/resuming procedure.

Cc: stable@vger.kernel.org # 6.13.x because no drivers in 6.12.x
Fixes: 6b93bb41 ("printk: Add non-BKL (nbcon) console basic infrastructure")
Closes: https://lore.kernel.org/lkml/DB9PR04MB8429E7DDF2D93C2695DE401D92C4A@DB9PR04MB8429.eurprd04.prod.outlook.com


Signed-off-by: default avatarJohn Ogness <john.ogness@linutronix.de>
Reviewed-by: default avatarPetr Mladek <pmladek@suse.com>
Tested-by: default avatarSherry Sun <sherry.sun@nxp.com>
Link: https://patch.msgid.link/20251113160351.113031-3-john.ogness@linutronix.de


Signed-off-by: default avatarPetr Mladek <pmladek@suse.com>
parent d01ff281

kernel/printk/internal.h

+5 −3
Original line number Diff line number Diff line
@@ -230,6 +230,8 @@ struct console_flush_type { 
	bool	legacy_offload;

};



extern bool console_irqwork_blocked;



/*

 * Identify which console flushing methods should be used in the context of

 * the caller.
@@ -241,7 +243,7 @@ static inline void printk_get_console_flush_type(struct console_flush_type *ft) 
	switch (nbcon_get_default_prio()) {

	case NBCON_PRIO_NORMAL:

		if (have_nbcon_console && !have_boot_console) {

			if (printk_kthreads_running)

			if (printk_kthreads_running && !console_irqwork_blocked)

				ft->nbcon_offload = true;

			else

				ft->nbcon_atomic = true;
@@ -251,7 +253,7 @@ static inline void printk_get_console_flush_type(struct console_flush_type *ft) 
		if (have_legacy_console || have_boot_console) {

			if (!is_printk_legacy_deferred())

				ft->legacy_direct = true;

			else

			else if (!console_irqwork_blocked)

				ft->legacy_offload = true;

		}

		break;
@@ -264,7 +266,7 @@ static inline void printk_get_console_flush_type(struct console_flush_type *ft) 
		if (have_legacy_console || have_boot_console) {

			if (!is_printk_legacy_deferred())

				ft->legacy_direct = true;

			else

			else if (!console_irqwork_blocked)

				ft->legacy_offload = true;

		}

		break;

kernel/printk/nbcon.c

+7 −0
Original line number Diff line number Diff line
@@ -1276,6 +1276,13 @@ void nbcon_kthreads_wake(void) 
	if (!printk_kthreads_running)

		return;



	/*

	 * It is not allowed to call this function when console irq_work

	 * is blocked.

	 */

	if (WARN_ON_ONCE(console_irqwork_blocked))

		return;



	cookie = console_srcu_read_lock();

	for_each_console_srcu(con) {

		if (!(console_srcu_read_flags(con) & CON_NBCON))

kernel/printk/printk.c

+43 −15
Original line number Diff line number Diff line
@@ -462,6 +462,9 @@ bool have_boot_console; 
/* See printk_legacy_allow_panic_sync() for details. */

bool legacy_allow_panic_sync;



/* Avoid using irq_work when suspending. */

bool console_irqwork_blocked;



#ifdef CONFIG_PRINTK

DECLARE_WAIT_QUEUE_HEAD(log_wait);

static DECLARE_WAIT_QUEUE_HEAD(legacy_wait);
@@ -2426,7 +2429,7 @@ asmlinkage int vprintk_emit(int facility, int level, 


	if (ft.legacy_offload)

		defer_console_output();

	else

	else if (!console_irqwork_blocked)

		wake_up_klogd();



	return printed_len;
@@ -2730,10 +2733,20 @@ void console_suspend_all(void) 
{

	struct console *con;



	if (!console_suspend_enabled)

		return;

	if (console_suspend_enabled)

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



	/*

	 * Flush any console backlog and then avoid queueing irq_work until

	 * console_resume_all(). Until then deferred printing is no longer

	 * triggered, NBCON consoles transition to atomic flushing, and

	 * any klogd waiters are not triggered.

	 */

	pr_flush(1000, true);

	console_irqwork_blocked = true;



	if (!console_suspend_enabled)

		return;



	console_list_lock();

	for_each_console(con)
@@ -2754,9 +2767,14 @@ void console_resume_all(void) 
	struct console_flush_type ft;

	struct console *con;



	if (!console_suspend_enabled)

		return;

	/*

	 * Allow queueing irq_work. After restoring console state, deferred

	 * printing and any klogd waiters need to be triggered in case there

	 * is now a console backlog.

	 */

	console_irqwork_blocked = false;



	if (console_suspend_enabled) {

		console_list_lock();

		for_each_console(con)

			console_srcu_write_flags(con, con->flags & ~CON_SUSPENDED);
@@ -2768,12 +2786,15 @@ void console_resume_all(void) 
		 * that they are guaranteed to wake up and resume printing.

		 */

		synchronize_srcu(&console_srcu);

	}



	printk_get_console_flush_type(&ft);

	if (ft.nbcon_offload)

		nbcon_kthreads_wake();

	if (ft.legacy_offload)

		defer_console_output();

	else

		wake_up_klogd();



	pr_flush(1000, true);

}
@@ -4511,6 +4532,13 @@ static void __wake_up_klogd(int val) 
	if (!printk_percpu_data_ready())

		return;



	/*

	 * It is not allowed to call this function when console irq_work

	 * is blocked.

	 */

	if (WARN_ON_ONCE(console_irqwork_blocked))

		return;



	preempt_disable();

	/*

	 * Guarantee any new records can be seen by tasks preparing to wait