On Fri, May 25, 2012 at 04:03:27PM +0800, Asias He wrote:
> 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+ #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: Rusty Russell <[email protected]>
> Cc: "Michael S. Tsirkin" <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Signed-off-by: Asias He <[email protected]>
It may also be worth pointing out that external lock
is inherently broken - it's kept around for historical reasons
only.
See also this discussion
https://lkml.org/lkml/2012/5/28/72
Note: a bugfix so 3.5 material I think.
Acked-by: Michael S. Tsirkin <[email protected]>
> ---
> drivers/block/virtio_blk.c | 9 +++------
> 1 file changed, 3 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index b4fa2d7..774c31d 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -21,8 +21,6 @@ struct workqueue_struct *virtblk_wq;
>
> struct virtio_blk
> {
> - spinlock_t lock;
> -
> struct virtio_device *vdev;
> struct virtqueue *vq;
>
> @@ -65,7 +63,7 @@ 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;
>
> @@ -99,7 +97,7 @@ 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,
> @@ -431,7 +429,6 @@ static int __devinit virtblk_probe(struct virtio_device
> *vdev)
> goto out_free_index;
> }
>
> - spin_lock_init(&vblk->lock);
> vblk->vdev = vdev;
> vblk->sg_elems = sg_elems;
> sg_init_table(vblk->sg, vblk->sg_elems);
> @@ -456,7 +453,7 @@ 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;
> --
> 1.7.10.2
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