dm: remove dm_request loop

Remove queue_io return value and a loop in dm_request.

IO may be submitted to a worker thread with queue_io().  queue_io() sets
DMF_QUEUE_IO_TO_THREAD so that all further IO is queued for the thread. When
the thread finishes its work, it clears DMF_QUEUE_IO_TO_THREAD and from this
point on, requests are submitted from dm_request again. This will be used
for processing barriers.

Remove the loop in dm_request. queue_io() can submit I/Os to the worker thread
even if DMF_QUEUE_IO_TO_THREAD was not set.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 7 insertions, 15 deletions

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 9746c1eb9ef7..db022e5f3912 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -436,21 +436,18 @@ static void end_io_acct(struct dm_io *io)
 /*
  * Add the bio to the list of deferred io.
  */
-static int queue_io(struct mapped_device *md, struct bio *bio)
+static void queue_io(struct mapped_device *md, struct bio *bio)
 {
         down_write(&md->io_lock);
 
-        if (!test_bit(DMF_QUEUE_IO_TO_THREAD, &md->flags)) {
-                up_write(&md->io_lock);
-                return 1;
-        }
-
         spin_lock_irq(&md->deferred_lock);
         bio_list_add(&md->deferred, bio);
         spin_unlock_irq(&md->deferred_lock);
 
+        if (!test_and_set_bit(DMF_QUEUE_IO_TO_THREAD, &md->flags))
+                queue_work(md->wq, &md->work);
+
         up_write(&md->io_lock);
-        return 0;               /* deferred successfully */
 }
 
 /*
@@ -953,7 +950,7 @@ static int dm_request(struct request_queue *q, struct bio *bio)
          * If we're suspended or the thread is processing barriers
          * we have to queue this io for later.
          */
-        while (test_bit(DMF_QUEUE_IO_TO_THREAD, &md->flags)) {
+        if (unlikely(test_bit(DMF_QUEUE_IO_TO_THREAD, &md->flags))) {
                 up_read(&md->io_lock);
 
                 if (unlikely(test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags)) &&
@@ -962,14 +959,9 @@ static int dm_request(struct request_queue *q, struct bio *bio)
                         return 0;
                 }
 
-                if (!queue_io(md, bio))
-                        return 0;
+                queue_io(md, bio);
 
-                /*
-                 * We're in a while loop, because someone could suspend
-                 * before we get to the following read lock.
-                 */
-                down_read(&md->io_lock);
+                return 0;
         }
 
         __split_and_process_bio(md, bio);