diff options
author | Oleg Nesterov <oleg@redhat.com> | 2010-04-23 17:40:40 +0200 |
---|---|---|
committer | Tejun Heo <tj@kernel.org> | 2010-04-30 08:57:25 +0200 |
commit | 4d707b9f48e2c4aa94b96f1133813b73df71fb55 (patch) | |
tree | 2e8e6c44e55bcea9ae2de200ebb3edaac81c2a88 | |
parent | eef6a7d5c2f38adadab8240fabf43730fe796482 (diff) |
workqueue: change cancel_work_sync() to clear work->data
In short: change cancel_work_sync(work) to mark this work as "never
queued" upon return.
When cancel_work_sync(work) succeeds, we know that this work can't be
queued or running, and since we own WORK_STRUCT_PENDING nobody can change
the bits in work->data under us. This means we can also clear the "cwq"
part along with _PENDING bit lockless before return, unless the work is
queued nobody can assume get_wq_data() is stable even under cwq->lock.
This change can speedup the subsequent cancel/flush requests, and as
Dmitry pointed out this simplifies the usage of work_struct's which
can be queued on different workqueues. Consider this pseudo code from
the input subsystem:
struct workqueue_struct *WQ;
struct work_struct *WORK;
for (;;) {
WQ = create_workqueue();
...
if (condition())
queue_work(WQ, WORK);
...
cancel_work_sync(WORK);
destroy_workqueue(WQ);
}
If condition() returns T and then F, cancel_work_sync() will crash the
kernel because WORK->data still points to the already destroyed workqueue.
With this patch the code like above becomes correct.
Suggested-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
-rw-r--r-- | kernel/workqueue.c | 12 |
1 files changed, 11 insertions, 1 deletions
diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 0225fea8934..77dabbf64b8 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -229,6 +229,16 @@ static inline void set_wq_data(struct work_struct *work, atomic_long_set(&work->data, new); } +/* + * Clear WORK_STRUCT_PENDING and the workqueue on which it was queued. + */ +static inline void clear_wq_data(struct work_struct *work) +{ + unsigned long flags = *work_data_bits(work) & + (1UL << WORK_STRUCT_STATIC); + atomic_long_set(&work->data, flags); +} + static inline struct cpu_workqueue_struct *get_wq_data(struct work_struct *work) { @@ -671,7 +681,7 @@ static int __cancel_work_timer(struct work_struct *work, wait_on_work(work); } while (unlikely(ret < 0)); - work_clear_pending(work); + clear_wq_data(work); return ret; } |