Re: [PATCH v2 3/3] virtio-blk: Use block layer provided spinlock
From: "Michael S. Tsirkin" <mst@redhat.com>
Date: 2012-06-01 08:49:08
Also in:
kvm
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 <redacted>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: virtualization@lists.linux-foundation.org
Cc: kvm@vger.kernel.org
Signed-off-by: Asias He <redacted>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 <mst@redhat.com>
quoted hunk ↗ jump to hunk
--- 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