dm: improve BLK_STS_DM_REQUEUE and BLK_STS_AGAIN handling

If either BLK_STS_DM_REQUEUE or BLK_STS_AGAIN is returned for POLLED
io, we requeue the original bio into deferred list and kick md->wq to
re-submit it to block layer.

Improve the handling in the following way:

1) Factor out dm_handle_requeue() for handling dm_io requeue.

2) Unify handling for BLK_STS_DM_REQUEUE and BLK_STS_AGAIN: clear
   REQ_POLLED for BLK_STS_DM_REQUEUE too, for the sake of simplicity,
   given BLK_STS_DM_REQUEUE is very unusual.

3) Queue md->wq explicitly in dm_handle_requeue(), so requeue handling
   becomes more robust.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 84929bd..c987f9a 100644 (file)
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -880,22 +880,41 @@ static int __noflush_suspending(struct mapped_device *md)
        return test_bit(DMF_NOFLUSH_SUSPENDING, &md->flags);
 }
 
-static void dm_io_complete(struct dm_io *io)
+/*
+ * Return true if the dm_io's original bio is requeued.
+ * io->status is updated with error if requeue disallowed.
+ */
+static bool dm_handle_requeue(struct dm_io *io)
 {
-       blk_status_t io_error;
-       struct mapped_device *md = io->md;
        struct bio *bio = io->split_bio ? io->split_bio : io->orig_bio;
+       bool handle_requeue = (io->status == BLK_STS_DM_REQUEUE);
+       bool handle_polled_eagain = ((io->status == BLK_STS_AGAIN) &&
+                                    (bio->bi_opf & REQ_POLLED));
+       struct mapped_device *md = io->md;
+       bool requeued = false;
 
-       if (io->status == BLK_STS_DM_REQUEUE) {
+       if (handle_requeue || handle_polled_eagain) {
                unsigned long flags;
+
+               if (bio->bi_opf & REQ_POLLED) {
+                       /*
+                        * Upper layer won't help us poll split bio
+                        * (io->orig_bio may only reflect a subset of the
+                        * pre-split original) so clear REQ_POLLED.
+                        */
+                       bio_clear_polled(bio);
+               }
+
                /*
-                * Target requested pushing back the I/O.
+                * Target requested pushing back the I/O or
+                * polled IO hit BLK_STS_AGAIN.
                 */
                spin_lock_irqsave(&md->deferred_lock, flags);
-               if (__noflush_suspending(md) &&
-                   !WARN_ON_ONCE(dm_is_zone_write(md, bio))) {
-                       /* NOTE early return due to BLK_STS_DM_REQUEUE below */
+               if ((__noflush_suspending(md) &&
+                    !WARN_ON_ONCE(dm_is_zone_write(md, bio))) ||
+                   handle_polled_eagain) {
                        bio_list_add_head(&md->deferred, bio);
+                       requeued = true;
                } else {
                        /*
                         * noflush suspend was interrupted or this is
@@ -906,6 +925,21 @@ static void dm_io_complete(struct dm_io *io)
                spin_unlock_irqrestore(&md->deferred_lock, flags);
        }
 
+       if (requeued)
+               queue_work(md->wq, &md->work);
+
+       return requeued;
+}
+
+static void dm_io_complete(struct dm_io *io)
+{
+       struct bio *bio = io->split_bio ? io->split_bio : io->orig_bio;
+       struct mapped_device *md = io->md;
+       blk_status_t io_error;
+       bool requeued;
+
+       requeued = dm_handle_requeue(io);
+
        io_error = io->status;
        if (dm_io_flagged(io, DM_IO_ACCOUNTED))
                dm_end_io_acct(io);
@@ -925,23 +959,9 @@ static void dm_io_complete(struct dm_io *io)
        if (unlikely(wq_has_sleeper(&md->wait)))
                wake_up(&md->wait);
 
-       if (io_error == BLK_STS_DM_REQUEUE || io_error == BLK_STS_AGAIN) {
-               if (bio->bi_opf & REQ_POLLED) {
-                       /*
-                        * Upper layer won't help us poll split bio (io->orig_bio
-                        * may only reflect a subset of the pre-split original)
-                        * so clear REQ_POLLED in case of requeue.
-                        */
-                       bio_clear_polled(bio);
-                       if (io_error == BLK_STS_AGAIN) {
-                               /* io_uring doesn't handle BLK_STS_AGAIN (yet) */
-                               queue_io(md, bio);
-                               return;
-                       }
-               }
-               if (io_error == BLK_STS_DM_REQUEUE)
-                       return;
-       }
+       /* Return early if the original bio was requeued */
+       if (requeued)
+               return;
 
        if (bio_is_flush_with_data(bio)) {
                /*