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().
-- Jamie
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