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authorOleg Nesterov <oleg@redhat.com>2010-04-23 17:40:40 +0200
committerTejun Heo <tj@kernel.org>2010-04-30 08:57:25 +0200
commit4d707b9f48e2c4aa94b96f1133813b73df71fb55 (patch)
tree2e8e6c44e55bcea9ae2de200ebb3edaac81c2a88 /kernel/workqueue.c
parenteef6a7d5c2f38adadab8240fabf43730fe796482 (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>
Diffstat (limited to 'kernel/workqueue.c')
-rw-r--r--kernel/workqueue.c12
1 files changed, 11 insertions, 1 deletions
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 0225fea89340..77dabbf64b8f 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;
}