Gitweb: http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=db7008...
Commit: db700897224b5ebdf852f2d38920ce428940d059
Parent: 1a4d9b0aa0d3c50314e57525a5e5ec2cfc48b4c8
Author: Oleg Nesterov <oleg@tv-sign.ru>
AuthorDate: Fri Jul 25 01:47:49 2008 -0700
Committer: Linus Torvalds <torvalds@linux-foundation.org>
CommitDate: Fri Jul 25 10:53:40 2008 -0700
workqueues: implement flush_work()
Most of users of flush_workqueue() can be changed to use cancel_work_sync(),
but sometimes we really need to wait for the completion and cancelling is not
an option. schedule_on_each_cpu() is good example.
Add the new helper, flush_work(work), which waits for the completion of the
specific work_struct. More precisely, it "flushes" the result of of the last
queue_work() which is visible to the caller.
For example, this code
queue_work(wq, work);
/* WINDOW */
queue_work(wq, work);
flush_work(work);
doesn't necessary work "as expected". What can happen in the WINDOW above is
- wq starts the execution of work->func()
- the caller migrates to another CPU
now, after the 2nd queue_work() this work is active on the previous CPU, and
at the same time it is queued on another. In this case flush_work(work) may
return before the first work->func() completes.
It is trivial to add another helper
int flush_work_sync(struct work_struct *work)
{
return flush_work(work) || wait_on_work(work);
}
which works "more correctly", but it has to iterate over all CPUs and thus
it much slower than flush_work().
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Max Krasnyansky <maxk@qualcomm.com>
Acked-by: Jarek Poplawski <jarkao2@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
include/linux/workqueue.h | 2 +
kernel/workqueue.c | 46 +++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 48 insertions(+), 0 deletions(-)
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 14d4712..5c158c4 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -201,6 +201,8 @@ extern int keventd_up(void);
extern void init_workqueues(void);
int execute_in_process_context(work_func_t fn, struct execute_work *);
+extern int flush_work(struct work_struct *work);
+
extern int cancel_work_sync(struct work_struct *work);
/*
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index d9a2d65..ee41cf8 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -423,6 +423,52 @@ void flush_workqueue(struct workqueue_struct *wq)
}
EXPORT_SYMBOL_GPL(flush_workqueue);
+/**
+ * flush_work - block until a work_struct's callback has terminated
+ * @work: the work which is to be flushed
+ *
+ * It is expected that, prior to calling flush_work(), the caller has
+ * arranged for the work to not be requeued, otherwise it doesn't make
+ * sense to use this function.
+ */
+int flush_work(struct work_struct *work)
+{
+ struct cpu_workqueue_struct *cwq;
+ struct list_head *prev;
+ struct wq_barrier barr;
+
+ might_sleep();
+ cwq = get_wq_data(work);
+ if (!cwq)
+ return 0;
+
+ prev = NULL;
+ spin_lock_irq(&cwq->lock);
+ if (!list_empty(&work->entry)) {
+ /*
+ * See the comment near try_to_grab_pending()->smp_rmb().
+ * If it was re-queued under us we are not going to wait.
+ */
+ smp_rmb();
+ if (unlikely(cwq != get_wq_data(work)))
+ goto out;
+ prev = &work->entry;
+ } else {
+ if (cwq->current_work != work)
+ goto out;
+ prev = &cwq->worklist;
+ }
+ insert_wq_barrier(cwq, &barr, prev->next);
+out:
+ spin_unlock_irq(&cwq->lock);
+ if (!prev)
+ return 0;
+
+ wait_for_completion(&barr.done);
+ return 1;
+}
+EXPORT_SYMBOL_GPL(flush_work);
+
/*
* Upon a successful return (>= 0), the caller "owns" WORK_STRUCT_PENDING bit,
* so this work can't be re-armed in any way.
--
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