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timekeeping: Add a lockdep override in tick_freeze()

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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: Borislav Petkov <bp@alien8.de>
Reported-by: Chris Bainbridge <chris.bainbridge@gmail.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter 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/
This commit is contained in:
Sebastian Andrzej Siewior 2025-04-04 15:34:29 +02:00 committed by Thomas Gleixner
parent 2424e146be
commit 92e250c624
1 changed files with 22 additions and 0 deletions
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22
kernel/time/tick-common.c
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@ -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);