virtio-blk: Use block layer provided spinlock

BugLink: http://bugs.launchpad.net/bugs/1035435

commit 2c95a32 upstream.

Block layer will allocate a spinlock for the queue if the driver does
not provide one in blk_init_queue().

The reason to use the internal spinlock is that blk_cleanup_queue() will
switch to use the internal spinlock in the cleanup code path.

        if (q->queue_lock != &q->__queue_lock)
                q->queue_lock = &q->__queue_lock;

However, processes which are in D state might have taken the driver
provided spinlock, when the processes wake up, they would release the
block provided spinlock.

=====================================
[ BUG: bad unlock balance detected! ]
3.4.0-rc7+ torvalds#238 Not tainted
-------------------------------------
fio/3587 is trying to release lock (&(&q->__queue_lock)->rlock) at:
[<ffffffff813274d2>] blk_queue_bio+0x2a2/0x380
but there are no more locks to release!

other info that might help us debug this:
1 lock held by fio/3587:
 #0:  (&(&vblk->lock)->rlock){......}, at:
[<ffffffff8132661a>] get_request_wait+0x19a/0x250

Other drivers use block layer provided spinlock as well, e.g. SCSI.

Switching to the block layer provided spinlock saves a bit of memory and
does not increase lock contention. Performance test shows no real
difference is observed before and after this patch.

Changes in v2: Improve commit log as Michael suggested.

Cc: [email protected]
Cc: [email protected]
Signed-off-by: Asias He <[email protected]>
Acked-by: Michael S. Tsirkin <[email protected]>
Signed-off-by: Rusty Russell <[email protected]>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <[email protected]>
Signed-off-by: Herton Ronaldo Krzesinski <[email protected]>

drivers/block/virtio_blk.c

@@ -20,8 +20,6 @@ struct workqueue_struct *virtblk_wq;
 
 struct virtio_blk
 {
- spinlock_t lock;
-
  struct virtio_device *vdev;
  struct virtqueue *vq;
 
@@ -62,7 +60,7 @@ static void blk_done(struct virtqueue *vq)
  unsigned int len;
  unsigned long flags;
 
- spin_lock_irqsave(&vblk->lock, flags);
+ spin_lock_irqsave(vblk->disk->queue->queue_lock, flags);
  while ((vbr = virtqueue_get_buf(vblk->vq, &len)) != NULL) {
  int error;
 
@@ -97,7 +95,7 @@ static void blk_done(struct virtqueue *vq)
  }
  /* In case queue is stopped waiting for more buffers. */
  blk_start_queue(vblk->disk->queue);
- spin_unlock_irqrestore(&vblk->lock, flags);
+ spin_unlock_irqrestore(vblk->disk->queue->queue_lock, flags);
 }
 
 static bool do_req(struct request_queue *q, struct virtio_blk *vblk,
@@ -384,7 +382,6 @@ static int __devinit virtblk_probe(struct virtio_device *vdev)
  }
 
  INIT_LIST_HEAD(&vblk->reqs);
- spin_lock_init(&vblk->lock);
  vblk->vdev = vdev;
  vblk->sg_elems = sg_elems;
  sg_init_table(vblk->sg, vblk->sg_elems);
@@ -410,7 +407,7 @@ static int __devinit virtblk_probe(struct virtio_device *vdev)
  goto out_mempool;
  }
 
- q = vblk->disk->queue = blk_init_queue(do_virtblk_request, &vblk->lock);
+ q = vblk->disk->queue = blk_init_queue(do_virtblk_request, NULL);
  if (!q) {
  err = -ENOMEM;
  goto out_put_disk;