irq_work: Allow irq_work_sync() to sleep if irq_work() no IRQ support.

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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20211006111852.1514359-3-bigeasy@linutronix.de

diff --git a/include/linux/irq_work.h b/include/linux/irq_work.h
index ec2a47a81e423d244d8c5abe23602c654f732ed7..b48955e9c920e32e09fcf9c0041cc720dbebe819 100644 (file)
--- 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 db8c248ebc8c81a9596bbc46ecd2583f85f62e24..e789beda8297dc3e9ab112110c2e94b4a848c880 100644 (file)
--- 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();