Re: [PATCH 05/10] writeback: support > 1 flusher thread per bdi

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Jamie Lokier wrote:
Artem Bityutskiy wrote:
Jens Axboe wrote:
+static void bdi_queue_work(struct backing_dev_info *bdi, struct bdi_work *work)
+{
+	if (work) {
+		work->seen = bdi->wb_mask;
+		BUG_ON(!work->seen);
+		atomic_set(&work->pending, bdi->wb_cnt);
+		BUG_ON(!bdi->wb_cnt);
+
+		/*
+		 * Make sure stores are seen before it appears on the list
+		 */
+		smp_mb();
+
+		spin_lock(&bdi->wb_lock);
+		list_add_tail_rcu(&work->list, &bdi->work_list);
+		spin_unlock(&bdi->wb_lock);
+	}
Doesn't spin_lock() include an implicit memory barrier?
After &bdi->wb_lock is acquired, it is guaranteed that all
memory operations are finished.

I'm pretty sure spin_lock() is an "acquire" barrier, which just guarantees
loads/stores after the spin_lock() are done after taking the lock.

It doesn't guarantee anything about loads/stores before the spin_lock().

Right, but comment says memops should be flushed before the
list is changed.

--
Best Regards,
Artem Bityutskiy (Артём Битюцкий)
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