reimplement flush_workqueue()
Remove ->remove_sequence, ->insert_sequence, and ->work_done from struct
cpu_workqueue_struct. To implement flush_workqueue() we can queue a
barrier work on each CPU and wait for its completition.
The barrier is queued under workqueue_mutex to ensure that per cpu
wq->cpu_wq is alive, we drop this mutex before going to sleep. If CPU goes
down while we are waiting for completition, take_over_work() will move the
barrier on another CPU, and the handler will wake up us eventually.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 1ea4bcb..b7bb37a 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -36,23 +36,13 @@
/*
* The per-CPU workqueue (if single thread, we always use the first
* possible cpu).
- *
- * The sequence counters are for flush_scheduled_work(). It wants to wait
- * until all currently-scheduled works are completed, but it doesn't
- * want to be livelocked by new, incoming ones. So it waits until
- * remove_sequence is >= the insert_sequence which pertained when
- * flush_scheduled_work() was called.
*/
struct cpu_workqueue_struct {
spinlock_t lock;
- long remove_sequence; /* Least-recently added (next to run) */
- long insert_sequence; /* Next to add */
-
struct list_head worklist;
wait_queue_head_t more_work;
- wait_queue_head_t work_done;
struct workqueue_struct *wq;
struct task_struct *thread;
@@ -138,8 +128,6 @@
f(work);
spin_lock_irqsave(&cwq->lock, flags);
- cwq->remove_sequence++;
- wake_up(&cwq->work_done);
ret = 1;
}
spin_unlock_irqrestore(&cwq->lock, flags);
@@ -187,7 +175,6 @@
spin_lock_irqsave(&cwq->lock, flags);
set_wq_data(work, cwq);
list_add_tail(&work->entry, &cwq->worklist);
- cwq->insert_sequence++;
wake_up(&cwq->more_work);
spin_unlock_irqrestore(&cwq->lock, flags);
}
@@ -338,8 +325,6 @@
}
spin_lock_irqsave(&cwq->lock, flags);
- cwq->remove_sequence++;
- wake_up(&cwq->work_done);
}
cwq->run_depth--;
spin_unlock_irqrestore(&cwq->lock, flags);
@@ -394,6 +379,25 @@
return 0;
}
+struct wq_barrier {
+ struct work_struct work;
+ struct completion done;
+};
+
+static void wq_barrier_func(struct work_struct *work)
+{
+ struct wq_barrier *barr = container_of(work, struct wq_barrier, work);
+ complete(&barr->done);
+}
+
+static inline void init_wq_barrier(struct wq_barrier *barr)
+{
+ INIT_WORK(&barr->work, wq_barrier_func);
+ __set_bit(WORK_STRUCT_PENDING, work_data_bits(&barr->work));
+
+ init_completion(&barr->done);
+}
+
static void flush_cpu_workqueue(struct cpu_workqueue_struct *cwq)
{
if (cwq->thread == current) {
@@ -401,23 +405,18 @@
* Probably keventd trying to flush its own queue. So simply run
* it by hand rather than deadlocking.
*/
+ mutex_unlock(&workqueue_mutex);
run_workqueue(cwq);
+ mutex_lock(&workqueue_mutex);
} else {
- DEFINE_WAIT(wait);
- long sequence_needed;
+ struct wq_barrier barr;
- spin_lock_irq(&cwq->lock);
- sequence_needed = cwq->insert_sequence;
+ init_wq_barrier(&barr);
+ __queue_work(cwq, &barr.work);
- while (sequence_needed - cwq->remove_sequence > 0) {
- prepare_to_wait(&cwq->work_done, &wait,
- TASK_UNINTERRUPTIBLE);
- spin_unlock_irq(&cwq->lock);
- schedule();
- spin_lock_irq(&cwq->lock);
- }
- finish_wait(&cwq->work_done, &wait);
- spin_unlock_irq(&cwq->lock);
+ mutex_unlock(&workqueue_mutex);
+ wait_for_completion(&barr.done);
+ mutex_lock(&workqueue_mutex);
}
}
@@ -428,29 +427,25 @@
* Forces execution of the workqueue and blocks until its completion.
* This is typically used in driver shutdown handlers.
*
- * This function will sample each workqueue's current insert_sequence number and
- * will sleep until the head sequence is greater than or equal to that. This
- * means that we sleep until all works which were queued on entry have been
- * handled, but we are not livelocked by new incoming ones.
+ * We sleep until all works which were queued on entry have been handled,
+ * but we are not livelocked by new incoming ones.
*
* This function used to run the workqueues itself. Now we just wait for the
* helper threads to do it.
*/
void fastcall flush_workqueue(struct workqueue_struct *wq)
{
- might_sleep();
-
+ mutex_lock(&workqueue_mutex);
if (is_single_threaded(wq)) {
/* Always use first cpu's area. */
flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, singlethread_cpu));
} else {
int cpu;
- mutex_lock(&workqueue_mutex);
for_each_online_cpu(cpu)
flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, cpu));
- mutex_unlock(&workqueue_mutex);
}
+ mutex_unlock(&workqueue_mutex);
}
EXPORT_SYMBOL_GPL(flush_workqueue);
@@ -463,12 +458,9 @@
spin_lock_init(&cwq->lock);
cwq->wq = wq;
cwq->thread = NULL;
- cwq->insert_sequence = 0;
- cwq->remove_sequence = 0;
cwq->freezeable = freezeable;
INIT_LIST_HEAD(&cwq->worklist);
init_waitqueue_head(&cwq->more_work);
- init_waitqueue_head(&cwq->work_done);
if (is_single_threaded(wq))
p = kthread_create(worker_thread, cwq, "%s", wq->name);