[PATCH AUTOSEL 6.14 30/34] timekeeping: Add a lockdep override in tick_freeze()

Sasha Levin
2025-04-14T13:27:20Z

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

[ Upstream commit 92e250c624ea37fde64bfd624fd2556f0d846f18 ]

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/
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/time/tick-common.c | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)

diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index a47bcf71defcf..9a3859443c042 100644
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -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);
--
2.39.5