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 <[email protected]> --- 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 _______________________________________________ Virtualization mailing list [email protected] https://lists.linuxfoundation.org/mailman/listinfo/virtualization
