1 files changed, 74 insertions, 0 deletions
diff --git a/debian/patches-rt/0002_irq_work_allow_irq_work_sync_to_sleep_if_irq_work_no_irq_support.patch b/debian/patches-rt/0002_irq_work_allow_irq_work_sync_to_sleep_if_irq_work_no_irq_support.patch
new file mode 100644
index 000000000..c273e441b
--- /dev/null
+++ b/debian/patches-rt/0002_irq_work_allow_irq_work_sync_to_sleep_if_irq_work_no_irq_support.patch
@@ -0,0 +1,74 @@
+From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+Subject: irq_work: Allow irq_work_sync() to sleep if irq_work() no IRQ support.
+Date: Wed, 06 Oct 2021 13:18:50 +0200
+Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.15/older/patches-5.15.3-rt21.tar.xz
+
+irq_work() triggers instantly an interrupt if supported by the
+architecture. Otherwise the work will be processed on the next timer
+tick. In worst case irq_work_sync() could spin up to a jiffy.
+
+irq_work_sync() is usually used in tear down context which is fully
+preemptible. Based on review irq_work_sync() is invoked from preemptible
+context and there is one waiter at a time. This qualifies it to use
+rcuwait for synchronisation.
+
+Let irq_work_sync() synchronize with rcuwait if the architecture
+processes irqwork via the timer tick.
+
+Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+Link: https://lore.kernel.org/r/20211006111852.1514359-3-bigeasy@linutronix.de
+---
+ include/linux/irq_work.h |    3 +++
+ kernel/irq_work.c        |   10 ++++++++++
+ 2 files changed, 13 insertions(+)
+
+--- a/include/linux/irq_work.h
++++ b/include/linux/irq_work.h
+@@ -3,6 +3,7 @@
+ #define _LINUX_IRQ_WORK_H
+ 
+ #include <linux/smp_types.h>
++#include <linux/rcuwait.h>
+ 
+ /*
+  * An entry can be in one of four states:
+@@ -16,11 +17,13 @@
+ struct irq_work {
+ 	struct __call_single_node node;
+ 	void (*func)(struct irq_work *);
++	struct rcuwait irqwait;
+ };
+ 
+ #define __IRQ_WORK_INIT(_func, _flags) (struct irq_work){	\
+ 	.node = { .u_flags = (_flags), },			\
+ 	.func = (_func),					\
++	.irqwait = __RCUWAIT_INITIALIZER(irqwait),		\
+ }
+ 
+ #define IRQ_WORK_INIT(_func) __IRQ_WORK_INIT(_func, 0)
+--- a/kernel/irq_work.c
++++ b/kernel/irq_work.c
+@@ -160,6 +160,9 @@ void irq_work_single(void *arg)
+ 	 * else claimed it meanwhile.
+ 	 */
+ 	(void)atomic_cmpxchg(&work->node.a_flags, flags, flags & ~IRQ_WORK_BUSY);
++
++	if (!arch_irq_work_has_interrupt())
++		rcuwait_wake_up(&work->irqwait);
+ }
+ 
+ static void irq_work_run_list(struct llist_head *list)
+@@ -204,6 +207,13 @@ void irq_work_tick(void)
+ void irq_work_sync(struct irq_work *work)
+ {
+ 	lockdep_assert_irqs_enabled();
++	might_sleep();
++
++	if (!arch_irq_work_has_interrupt()) {
++		rcuwait_wait_event(&work->irqwait, !irq_work_is_busy(work),
++				   TASK_UNINTERRUPTIBLE);
++		return;
++	}
+ 
+ 	while (irq_work_is_busy(work))
+ 		cpu_relax();