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>
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@ -583,6 +583,8 @@ static void __devexit virtblk_remove(struct virtio_device *vdev)
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{
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struct virtio_blk *vblk = vdev->priv;
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int index = vblk->index;
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struct virtblk_req *vbr;
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unsigned long flags;
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/* Prevent config work handler from accessing the device. */
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mutex_lock(&vblk->config_lock);
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@ -598,6 +600,15 @@ static void __devexit virtblk_remove(struct virtio_device *vdev)
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flush_work(&vblk->config_work);
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del_gendisk(vblk->disk);
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/* Abort requests dispatched to driver. */
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spin_lock_irqsave(&vblk->lock, flags);
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while ((vbr = virtqueue_detach_unused_buf(vblk->vq))) {
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__blk_end_request_all(vbr->req, -EIO);
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mempool_free(vbr, vblk->pool);
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}
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spin_unlock_irqrestore(&vblk->lock, flags);
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blk_cleanup_queue(vblk->disk->queue);
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put_disk(vblk->disk);
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mempool_destroy(vblk->pool);
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