5.4.74-rt42-rc2 stable review patch. If anyone has any objections, please let me know.
------------------ From: Sebastian Andrzej Siewior <[email protected]> PREEMPT_RT does not spin and wait until a running timer completes its callback but instead it blocks on a sleeping lock to prevent a deadlock. This blocking can not be done for workqueue's IRQ_SAFE timer which will be canceled in an IRQ-off region. It has to happen to in IRQ-off region because changing the PENDING bit and clearing the timer must not be interrupted to avoid a busy-loop. The callback invocation of IRQSAFE timer is not preempted on PREEMPT_RT so there is no need to synchronize on timer_base::expiry_lock. Don't acquire the timer_base::expiry_lock for TIMER_IRQSAFE flagged timer. Add a lockdep annotation to ensure that this function is always invoked in preemptible context on PREEMPT_RT. Reported-by: Mike Galbraith <[email protected]> Signed-off-by: Sebastian Andrzej Siewior <[email protected]> Cc: [email protected] Signed-off-by: Steven Rostedt (VMware) <[email protected]> --- kernel/time/timer.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/kernel/time/timer.c b/kernel/time/timer.c index 89078fd848b9..3e9d7f227a5c 100644 --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -1289,7 +1289,7 @@ static void del_timer_wait_running(struct timer_list *timer) u32 tf; tf = READ_ONCE(timer->flags); - if (!(tf & TIMER_MIGRATING)) { + if (!(tf & (TIMER_MIGRATING | TIMER_IRQSAFE))) { struct timer_base *base = get_timer_base(tf); /* @@ -1373,6 +1373,13 @@ int del_timer_sync(struct timer_list *timer) */ WARN_ON(in_irq() && !(timer->flags & TIMER_IRQSAFE)); + /* + * Must be able to sleep on PREEMPT_RT because of the slowpath in + * del_timer_wait_running(). + */ + if (IS_ENABLED(CONFIG_PREEMPT_RT) && !(timer->flags & TIMER_IRQSAFE)) + might_sleep(); + do { ret = try_to_del_timer_sync(timer); -- 2.28.0
