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-rw-r--r--debian/patches-rt/0067-timers-Don-t-block-on-expiry_lock-for-TIMER_IRQSAFE.patch60
1 files changed, 60 insertions, 0 deletions
diff --git a/debian/patches-rt/0067-timers-Don-t-block-on-expiry_lock-for-TIMER_IRQSAFE.patch b/debian/patches-rt/0067-timers-Don-t-block-on-expiry_lock-for-TIMER_IRQSAFE.patch
new file mode 100644
index 000000000..01c62e677
--- /dev/null
+++ b/debian/patches-rt/0067-timers-Don-t-block-on-expiry_lock-for-TIMER_IRQSAFE.patch
@@ -0,0 +1,60 @@
+From a7d720657001cb31fc09699861f12726418a4bf8 Mon Sep 17 00:00:00 2001
+From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+Date: Mon, 2 Nov 2020 14:14:24 +0100
+Subject: [PATCH 067/323] timers: Don't block on ->expiry_lock for
+ TIMER_IRQSAFE
+Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.10/older/patches-5.10.204-rt100.tar.xz
+
+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 <efault@gmx.de>
+Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+Cc: stable-rt@vger.kernel.org
+---
+ 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 e87e638c31bd..a4fdc7cfb723 100644
+--- a/kernel/time/timer.c
++++ b/kernel/time/timer.c
+@@ -1287,7 +1287,7 @@ 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);
+
+ /*
+@@ -1371,6 +1371,13 @@ 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))
++ lockdep_assert_preemption_enabled();
++
+ do {
+ ret = try_to_del_timer_sync(timer);
+
+--
+2.43.0
+