Merge branch 'for-3.16/drivers' of git://git.kernel.dk/linux-block into next

Pull block driver changes from Jens Axboe:
 "Now that the core bits are in, here's the pull request for the driver
  related changes for 3.16.  Nothing out of the ordinary here, mostly
  business as usual.  There are a few pulls of for-3.16/core into this
  branch, which were done when the blk-mq was modified after the
  mtip32xx conversion was put in.

  The pull request contains:

   - skd and cciss converted to use pci_enable_msix_exact().  From
     Alexander Gordeev.

   - A few mtip32xx fixes from Asai @ Micron.

   - The conversion of mtip32xx from make_request_fn to blk-mq, and a
     later small fix for that conversion on quiescing for non-queued IO.
     From me.

   - A fix for bsg to use an exported function to check whether this
     driver is request based or not.  Needed updating for blk-mq, which
     is request based, but does not have a request_fn hook.  From me.

   - Small floppy bug fix from Jiri.

   - A series of cleanups for the cdrom uniform layer from Joe Perches.
     Gets rid of various old ugly macros, making the code conform more
     to the modern coding style.

   - A series of patches for drbd from the drbd crew (Lars Ellenberg and
     Philipp Reisner).

   - A use-after-free fix for null_blk from Ming Lei.

   - Also from Ming Lei is a performance patch for virtio-blk, which can
     net us a 3x win on kvm platforms where world notification is
     expensive.

   - Ming Lei also fixed a stall issue in virtio-blk, due to a race
     between queue start/stop and resource limits.

   - A small batch of fixes for xen-blk{back,front} from Olaf Hering and
     Valentin Priescu"

* 'for-3.16/drivers' of git://git.kernel.dk/linux-block: (54 commits)
  block: virtio_blk: don't hold spin lock during world switch
  xen-blkback: defer freeing blkif to avoid blocking xenwatch
  xen blkif.h: fix comment typo in discard-alignment
  xen/blkback: disable discard feature if requested by toolstack
  xen-blkfront: remove type check from blkfront_setup_discard
  floppy: do not corrupt bio.bi_flags when reading block 0
  mtip32xx: move error handling to service thread
  virtio_blk: fix race between start and stop queue
  mtip32xx: stop block hardware queues before quiescing IO
  mtip32xx: blk_mq_init_queue() returns an ERR_PTR
  mtip32xx: convert to use blk-mq
  cdrom: Remove unnecessary prototype for cdrom_get_disc_info
  cdrom: Remove unnecessary prototype for cdrom_mrw_exit
  cdrom: Remove cdrom_count_tracks prototype
  cdrom: Remove cdrom_get_next_writeable prototype
  cdrom: Remove cdrom_get_last_written prototype
  cdrom: Move mmc_ioctls above cdrom_ioctl to remove unnecessary prototype
  cdrom: Remove unnecessary sanitize_format prototype
  cdrom: Remove unnecessary check_for_audio_disc prototype
  cdrom: Remove prototype for open_for_data
  ...

1 files changed, 6 insertions, 3 deletions

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index c8f286e8d80f..f63d358f3d93 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -162,6 +162,7 @@ static int virtio_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *req)
 	unsigned int num;
 	const bool last = (req->cmd_flags & REQ_END) != 0;
 	int err;
+	bool notify = false;
 
 	BUG_ON(req->nr_phys_segments + 2 > vblk->sg_elems);
 
@@ -214,10 +215,12 @@ static int virtio_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *req)
 		return BLK_MQ_RQ_QUEUE_ERROR;
 	}
 
-	if (last)
-		virtqueue_kick(vblk->vq);
-
+	if (last && virtqueue_kick_prepare(vblk->vq))
+		notify = true;
 	spin_unlock_irqrestore(&vblk->vq_lock, flags);
+
+	if (notify)
+		virtqueue_notify(vblk->vq);
 	return BLK_MQ_RQ_QUEUE_OK;
 }