On Wed, Jan 7, 2015 at 6:57 PM, Fam Zheng <famz@xxxxxxxxxx> wrote:
>
> There is a race condition in virtscsi_handle_event, when many device
> hotplug/unplug events flush in quickly.
>
> The scsi_remove_device in virtscsi_handle_transport_reset may trigger
> the BUG_ON in scsi_target_reap, because the state is altered behind it,
> probably by scsi_scan_host of another event. I'm able to reproduce it by
> repeatedly plugging and unplugging a scsi disk with the same lun number.
>
> To fix this, a single thread workqueue (local to the module) is added,
> which makes the scan work serialized. With this change, the panic goes
> away.
>
> Signed-off-by: Fam Zheng <famz@xxxxxxxxxx>
Reviewed-by: Venkatesh Srinivas <venkateshs@xxxxxxxxxx>
> ---
>
> v4: Addressing MST's comments:
> Use ordered workqueue, with WQ_FREEZABLE and WQ_MEM_RECLAIM flags.
> Coding style fixes.
>
> v3: Fix spacing and destroy order. (MST)
> ---
> drivers/scsi/virtio_scsi.c | 14 +++++++++++++-
> 1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c
> index c52bb5d..0db63b5 100644
> --- a/drivers/scsi/virtio_scsi.c
> +++ b/drivers/scsi/virtio_scsi.c
> @@ -120,6 +120,7 @@ struct virtio_scsi {
>
> static struct kmem_cache *virtscsi_cmd_cache;
> static mempool_t *virtscsi_cmd_pool;
> +static struct workqueue_struct *virtscsi_scan_wq;
>
> static inline struct Scsi_Host *virtio_scsi_host(struct virtio_device *vdev)
> {
> @@ -404,7 +405,7 @@ static void virtscsi_complete_event(struct virtio_scsi *vscsi, void *buf)
> struct virtio_scsi_event_node *event_node = buf;
>
> if (!vscsi->stop_events)
> - queue_work(system_freezable_wq, &event_node->work);
> + queue_work(virtscsi_scan_wq, &event_node->work);
> }
>
> static void virtscsi_event_done(struct virtqueue *vq)
> @@ -1119,6 +1120,14 @@ static int __init init(void)
> pr_err("mempool_create() for virtscsi_cmd_pool failed\n");
> goto error;
> }
> +
> + virtscsi_scan_wq =
> + alloc_ordered_workqueue("virtscsi-scan", WQ_FREEZABLE | WQ_MEM_RECLAIM);
> + if (!virtscsi_scan_wq) {
> + pr_err("create_singlethread_workqueue() for virtscsi_scan_wq failed\n");
> + goto error;
> + }
> +
> ret = register_virtio_driver(&virtio_scsi_driver);
> if (ret < 0)
> goto error;
> @@ -1126,6 +1135,8 @@ static int __init init(void)
> return 0;
>
> error:
> + if (virtscsi_scan_wq)
> + destroy_workqueue(virtscsi_scan_wq);
> if (virtscsi_cmd_pool) {
> mempool_destroy(virtscsi_cmd_pool);
> virtscsi_cmd_pool = NULL;
> @@ -1140,6 +1151,7 @@ error:
> static void __exit fini(void)
> {
> unregister_virtio_driver(&virtio_scsi_driver);
> + destroy_workqueue(virtscsi_scan_wq);
> mempool_destroy(virtscsi_cmd_pool);
> kmem_cache_destroy(virtscsi_cmd_cache);
> }
> --
> 1.9.3
>
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