[PATCH 3.4 44/88] virtio-blk: Fix hot-unplug race in remove method

Greg Kroah-Hartman
2014-06-10T00:24:54Z

From: Asias He <asias@redhat.com>

commit b79d866c8b7014a51f611a64c40546109beaf24a upstream.

If we reset the virtio-blk device before the requests already dispatched
to the virtio-blk driver from the block layer are finised, we will stuck
in blk_cleanup_queue() and the remove will fail.

blk_cleanup_queue() calls blk_drain_queue() to drain all requests queued
before DEAD marking. However it will never success if the device is
already stopped. We'll have q->in_flight[] > 0, so the drain will not
finish.

How to reproduce the race:
1. hot-plug a virtio-blk device
2. keep reading/writing the device in guest
3. hot-unplug while the device is busy serving I/O

Test:
~1000 rounds of hot-plug/hot-unplug test passed with this patch.

Changes in v3:
- Drop blk_abort_queue and blk_abort_request
- Use __blk_end_request_all to complete request dispatched to driver

Changes in v2:
- Drop req_in_flight
- Use virtqueue_detach_unused_buf to get request dispatched to driver

Signed-off-by: Asias He <asias@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: Yijing Wang <wangyijing@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/block/virtio_blk.c | 11 +++++++++++
1 file changed, 11 insertions(+)

--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -573,6 +573,8 @@ static void __devexit virtblk_remove(str
{
struct virtio_blk *vblk = vdev->priv;
int index = vblk->index;
+ struct virtblk_req *vbr;
+ unsigned long flags;

/* Prevent config work handler from accessing the device. */
mutex_lock(&vblk->config_lock);
@@ -585,6 +587,15 @@ static void __devexit virtblk_remove(str
flush_work(&vblk->config_work);

del_gendisk(vblk->disk);
+
+ /* Abort requests dispatched to driver. */
+ spin_lock_irqsave(&vblk->lock, flags);
+ while ((vbr = virtqueue_detach_unused_buf(vblk->vq))) {
+ __blk_end_request_all(vbr->req, -EIO);
+ mempool_free(vbr, vblk->pool);
+ }
+ spin_unlock_irqrestore(&vblk->lock, flags);
+
blk_cleanup_queue(vblk->disk->queue);
put_disk(vblk->disk);
mempool_destroy(vblk->pool);