diff options
| author | Sebastian Andrzej Siewior <bigeasy@linutronix.de> | 2025-04-04 15:34:29 +0200 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2025-04-09 22:30:39 +0200 |
| commit | 92e250c624ea37fde64bfd624fd2556f0d846f18 (patch) | |
| tree | 2fb516ce5853a4cfb5cfb7434d3f5d3ad1831b67 /kernel | |
| parent | 2424e146bee00ddb4d4f79d3224f54634ca8d2bc (diff) | |
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: 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/
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/time/tick-common.c | 22 |
1 files changed, 22 insertions, 0 deletions
diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c index a47bcf71defc..9a3859443c04 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); |