Commit b79d866c authored May 04, 2012 by Asias He Committed by Rusty Russell May 22, 2012

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: Asias He <asias@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

parent 90e03207

drivers/block/virtio_blk.c

+11 −0

Original line number	Diff line number	Diff line
		@@ -583,6 +583,8 @@ static void __devexit virtblk_remove(struct virtio_device *vdev)
		{
		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);
		@@ -598,6 +600,15 @@ static void __devexit virtblk_remove(struct virtio_device *vdev)
		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);

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