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Message-ID: <20061217223416.GA6872@tv-sign.ru>
Date: Mon, 18 Dec 2006 01:34:16 +0300
From: Oleg Nesterov <oleg@...sign.ru>
To: Andrew Morton <akpm@...l.org>
Cc: David Howells <dhowells@...hat.com>,
Christoph Hellwig <hch@...radead.org>,
Ingo Molnar <mingo@...e.hu>,
Linus Torvalds <torvalds@...l.org>,
linux-kernel@...r.kernel.org
Subject: [PATCH, RFC] 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.
We don't need to worry about CPU going down while we are are sleeping
on the completition. take_over_work() will move this work on another
CPU, and the handler will wake up us eventually.
NOTE: I removed 'int cpu' parameter, flush_workqueue() locks/unlocks
workqueue_mutex unconditionally. It may be restored, but I think it
doesn't make much sense, we take the mutex for the very short time,
and the code becomes simpler.
Signed-off-by: Oleg Nesterov <oleg@...sign.ru>
workqueue.c | 87 ++++++++++++++++++++----------------------------------------
1 files changed, 29 insertions(+), 58 deletions(-)
--- mm-6.20-rc1/kernel/workqueue.c~1_flush_q 2006-12-18 00:56:58.000000000 +0300
+++ mm-6.20-rc1/kernel/workqueue.c 2006-12-18 01:13:22.000000000 +0300
@@ -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 @@ static int __run_work(struct cpu_workque
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 @@ static void __queue_work(struct cpu_work
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 @@ static void run_workqueue(struct cpu_wor
}
spin_lock_irqsave(&cwq->lock, flags);
- cwq->remove_sequence++;
- wake_up(&cwq->work_done);
}
cwq->run_depth--;
spin_unlock_irqrestore(&cwq->lock, flags);
@@ -394,45 +379,39 @@ static int worker_thread(void *__cwq)
return 0;
}
-/*
- * If cpu == -1 it's a single-threaded workqueue and the caller does not hold
- * workqueue_mutex
- */
-static void flush_cpu_workqueue(struct cpu_workqueue_struct *cwq, int cpu)
+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 void flush_cpu_workqueue(struct cpu_workqueue_struct *cwq)
{
if (cwq->thread == current) {
/*
* Probably keventd trying to flush its own queue. So simply run
* it by hand rather than deadlocking.
*/
- if (cpu != -1)
- mutex_unlock(&workqueue_mutex);
+ mutex_unlock(&workqueue_mutex);
run_workqueue(cwq);
- if (cpu != -1)
- mutex_lock(&workqueue_mutex);
+ mutex_lock(&workqueue_mutex);
} else {
- DEFINE_WAIT(wait);
- long sequence_needed;
+ struct wq_barrier barr = {
+ .work = __WORK_INITIALIZER(barr.work, wq_barrier_func),
+ .done = COMPLETION_INITIALIZER_ONSTACK(barr.done),
+ };
- spin_lock_irq(&cwq->lock);
- sequence_needed = cwq->insert_sequence;
+ __set_bit(WORK_STRUCT_PENDING, &barr.work.management);
+ __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);
- if (cpu != -1)
- mutex_unlock(&workqueue_mutex);
- schedule();
- if (cpu != -1) {
- mutex_lock(&workqueue_mutex);
- if (!cpu_online(cpu))
- return; /* oops, CPU unplugged */
- }
- 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);
}
}
@@ -443,30 +422,25 @@ static void flush_cpu_workqueue(struct c
* 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),
- -1);
+ 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), cpu);
- mutex_unlock(&workqueue_mutex);
+ flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, cpu));
}
+ mutex_unlock(&workqueue_mutex);
}
EXPORT_SYMBOL_GPL(flush_workqueue);
@@ -479,12 +453,9 @@ static struct task_struct *create_workqu
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);
-
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