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Commit b79d866c authored by Asias He's avatar Asias He Committed by Rusty Russell
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virtio-blk: Fix hot-unplug race in remove method 



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: default avatarAsias He <asias@redhat.com>
Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
parent 90e03207

drivers/block/virtio_blk.c

+11 −0
Original line number Original line Diff line number Diff line
@@ -583,6 +583,8 @@ static void __devexit virtblk_remove(struct virtio_device *vdev) 
{

{

	struct virtio_blk *vblk = vdev->priv;

	struct virtio_blk *vblk = vdev->priv;

	int index = vblk->index;

	int index = vblk->index;

	struct virtblk_req *vbr;

	unsigned long flags;





	/* Prevent config work handler from accessing the device. */

	/* Prevent config work handler from accessing the device. */

	mutex_lock(&vblk->config_lock);

	mutex_lock(&vblk->config_lock);
@@ -598,6 +600,15 @@ static void __devexit virtblk_remove(struct virtio_device *vdev) 
	flush_work(&vblk->config_work);

	flush_work(&vblk->config_work);





	del_gendisk(vblk->disk);

	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);

	blk_cleanup_queue(vblk->disk->queue);

	put_disk(vblk->disk);

	put_disk(vblk->disk);

	mempool_destroy(vblk->pool);

	mempool_destroy(vblk->pool);