Hi,

在 2025/05/12 13:17, Christoph Hellwig 写道:
On Mon, May 12, 2025 at 09:19:23AM +0800, Yu Kuai wrote:
+static void llbitmap_unplug(struct mddev *mddev, bool sync)
+{
+       DECLARE_COMPLETION_ONSTACK(done);
+       struct llbitmap *llbitmap = mddev->bitmap;
+       struct llbitmap_unplug_work unplug_work = {
+               .llbitmap = llbitmap,
+               .done = &done,
+       };
+
+       if (!llbitmap_dirty(llbitmap))
+               return;
+
+       INIT_WORK_ONSTACK(&unplug_work.work, llbitmap_unplug_fn);
+       queue_work(md_llbitmap_unplug_wq, &unplug_work.work);
+       wait_for_completion(&done);
+       destroy_work_on_stack(&unplug_work.work);

Why is this deferring the work to a workqueue, but then synchronously
waits on it?

This is the same as old bitmap, by the fact that issue new IO and wait
for such IO to be done from submit_bio() context will deadlock.

1) bitmap bio must be done before this bio can be issued;
2) bitmap bio will be added to current->bio_list, and wait for this bio
to be issued;

Do you have a better sulution to this problem?

Thanks,
Kuai


.



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