Commit 92e250c6 authored by Sebastian Andrzej Siewior's avatar Sebastian Andrzej Siewior Committed by Thomas Gleixner
Browse files

timekeeping: Add a lockdep override in tick_freeze() 



tick_freeze() acquires a raw spinlock (tick_freeze_lock). Later in the
callchain (timekeeping_suspend() -> mc146818_avoid_UIP()) the RTC driver
acquires a spinlock which becomes a sleeping lock on PREEMPT_RT.  Lockdep
complains about this lock nesting.

Add a lockdep override for this special case and a comment explaining
why it is okay.

Reported-by: default avatarBorislav Petkov <bp@alien8.de>
Reported-by: default avatarChris Bainbridge <chris.bainbridge@gmail.com>
Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/all/20250404133429.pnAzf-eF@linutronix.de
Closes: https://lore.kernel.org/all/20250330113202.GAZ-krsjAnurOlTcp-@fat_crate.local/
Closes: https://lore.kernel.org/all/CAP-bSRZ0CWyZZsMtx046YV8L28LhY0fson2g4EqcwRAVN1Jk+Q@mail.gmail.com/
parent 2424e146

kernel/time/tick-common.c

+22 −0
Original line number Diff line number Diff line
@@ -509,6 +509,7 @@ void tick_resume(void) 


#ifdef CONFIG_SUSPEND

static DEFINE_RAW_SPINLOCK(tick_freeze_lock);

static DEFINE_WAIT_OVERRIDE_MAP(tick_freeze_map, LD_WAIT_SLEEP);

static unsigned int tick_freeze_depth;



/**
@@ -528,9 +529,22 @@ void tick_freeze(void) 
	if (tick_freeze_depth == num_online_cpus()) {

		trace_suspend_resume(TPS("timekeeping_freeze"),

				     smp_processor_id(), true);

		/*

		 * All other CPUs have their interrupts disabled and are

		 * suspended to idle. Other tasks have been frozen so there

		 * is no scheduling happening. This means that there is no

		 * concurrency in the system at this point. Therefore it is

		 * okay to acquire a sleeping lock on PREEMPT_RT, such as a

		 * spinlock, because the lock cannot be held by other CPUs

		 * or threads and acquiring it cannot block.

		 *

		 * Inform lockdep about the situation.

		 */

		lock_map_acquire_try(&tick_freeze_map);

		system_state = SYSTEM_SUSPEND;

		sched_clock_suspend();

		timekeeping_suspend();

		lock_map_release(&tick_freeze_map);

	} else {

		tick_suspend_local();

	}
@@ -552,8 +566,16 @@ void tick_unfreeze(void) 
	raw_spin_lock(&tick_freeze_lock);



	if (tick_freeze_depth == num_online_cpus()) {

		/*

		 * Similar to tick_freeze(). On resumption the first CPU may

		 * acquire uncontended sleeping locks while other CPUs block on

		 * tick_freeze_lock.

		 */

		lock_map_acquire_try(&tick_freeze_map);

		timekeeping_resume();

		sched_clock_resume();

		lock_map_release(&tick_freeze_map);



		system_state = SYSTEM_RUNNING;

		trace_suspend_resume(TPS("timekeeping_freeze"),

				     smp_processor_id(), false);