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
Signed-off-by: Asias He <asias@xxxxxxxxxx>
---
drivers/block/virtio_blk.c | 26 ++++++++++++++++++++++----
1 file changed, 22 insertions(+), 4 deletions(-)
diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 72fe55d..72b818b 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -46,6 +46,9 @@ struct virtio_blk
/* Ida index - used to track minor number allocations. */
int index;
+ /* Number of pending requests dispatched to driver. */
+ int req_in_flight;
+
/* Scatterlist: can be too big for stack. */
struct scatterlist sg[/*sg_elems*/];
};
@@ -95,6 +98,7 @@ static void blk_done(struct virtqueue *vq)
}
__blk_end_request_all(vbr->req, error);
+ vblk->req_in_flight--;
mempool_free(vbr, vblk->pool);
}
/* In case queue is stopped waiting for more buffers. */
@@ -190,6 +194,7 @@ static void do_virtblk_request(struct request_queue *q)
while ((req = blk_peek_request(q)) != NULL) {
BUG_ON(req->nr_phys_segments + 2 > vblk->sg_elems);
+ vblk->req_in_flight++;
/* If this request fails, stop queue and wait for something to
finish to restart it. */
@@ -443,7 +448,7 @@ static int __devinit virtblk_probe(struct virtio_device *vdev)
if (err)
goto out_free_vblk;
- vblk->pool = mempool_create_kmalloc_pool(1,sizeof(struct virtblk_req));
+ vblk->pool = mempool_create_kmalloc_pool(1, sizeof(struct virtblk_req));
if (!vblk->pool) {
err = -ENOMEM;
goto out_free_vq;
@@ -466,6 +471,7 @@ static int __devinit virtblk_probe(struct virtio_device *vdev)
virtblk_name_format("vd", index, vblk->disk->disk_name, DISK_NAME_LEN);
+ vblk->req_in_flight = 0;
vblk->disk->major = major;
vblk->disk->first_minor = index_to_minor(index);
vblk->disk->private_data = vblk;
@@ -576,22 +582,34 @@ static void __devexit virtblk_remove(struct virtio_device *vdev)
{
struct virtio_blk *vblk = vdev->priv;
int index = vblk->index;
+ unsigned long flags;
+ int req_in_flight;
/* Prevent config work handler from accessing the device. */
mutex_lock(&vblk->config_lock);
vblk->config_enable = false;
mutex_unlock(&vblk->config_lock);
+ /* Abort all request on the queue. */
+ blk_abort_queue(vblk->disk->queue);
+ del_gendisk(vblk->disk);
+
/* Stop all the virtqueues. */
vdev->config->reset(vdev);
-
+ vdev->config->del_vqs(vdev);
flush_work(&vblk->config_work);
- del_gendisk(vblk->disk);
+ /* Wait requests dispatched to device driver to finish. */
+ do {
+ spin_lock_irqsave(&vblk->lock, flags);
+ req_in_flight = vblk->req_in_flight;
+ spin_unlock_irqrestore(&vblk->lock, flags);
+ } while (req_in_flight != 0);
+
blk_cleanup_queue(vblk->disk->queue);
put_disk(vblk->disk);
+
mempool_destroy(vblk->pool);
- vdev->config->del_vqs(vdev);
kfree(vblk);
ida_simple_remove(&vd_index_ida, index);
}
--
1.7.10
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