[PATCH 3/5] irq_work: Allow irq_work_sync() to sleep if irq_work() no IRQ support.

From: Sebastian Andrzej Siewior
Date: Mon Sep 27 2021 - 17:19:41 EST


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@xxxxxxxxxxxxx>
---
include/linux/irq_work.h | 3 +++
kernel/irq_work.c | 10 ++++++++++
2 files changed, 13 insertions(+)

diff --git a/include/linux/irq_work.h b/include/linux/irq_work.h
index ec2a47a81e423..b48955e9c920e 100644
--- 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)
diff --git a/kernel/irq_work.c b/kernel/irq_work.c
index caf2edffa20d5..853af2cee3612 100644
--- 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();
--
2.33.0