workqueue: Remember whether a work item was on a BH workqueue

Add an off-queue flag, WORK_OFFQ_BH, that indicates whether the last
workqueue the work item was on was a BH one. This will be used to test
whether a work item is BH in cancel_sync path to implement atomic
cancel_sync'ing for BH work items.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <jiangshanlai@gmail.com>

kernel/workqueue.c

@@ -764,6 +764,11 @@ static int work_next_color(int color)
 	return (color + 1) % WORK_NR_COLORS;
 }
 
+static unsigned long pool_offq_flags(struct worker_pool *pool)
+{
+	return (pool->flags & POOL_BH) ? WORK_OFFQ_BH : 0;
+}
+
 /*
  * While queued, %WORK_STRUCT_PWQ is set and non flag bits of a work's data
  * contain the pointer to the queued pwq.  Once execution starts, the flag
@@ -2122,7 +2127,8 @@ static int try_to_grab_pending(struct work_struct *work, u32 cflags,
 		 * this destroys work->data needed by the next step, stash it.
 		 */
 		work_data = *work_data_bits(work);
-		set_work_pool_and_keep_pending(work, pool->id, 0);
+		set_work_pool_and_keep_pending(work, pool->id,
+					       pool_offq_flags(pool));
 
 		/* must be the last step, see the function comment */
 		pwq_dec_nr_in_flight(pwq, work_data);
@@ -3175,7 +3181,7 @@ __acquires(&pool->lock)
 	 * PENDING and queued state changes happen together while IRQ is
 	 * disabled.
 	 */
-	set_work_pool_and_clear_pending(work, pool->id, 0);
+	set_work_pool_and_clear_pending(work, pool->id, pool_offq_flags(pool));
 
 	pwq->stats[PWQ_STAT_STARTED]++;
 	raw_spin_unlock_irq(&pool->lock);