On Tue, 01/06 00:10, Michael S. Tsirkin wrote:
> On Mon, Jan 05, 2015 at 11:48:47AM -0800, Venkatesh Srinivas wrote:
> > On Sun, Jan 4, 2015 at 10:04 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 make is safe, the mutex added in struct virtio_scsi is held in
> > virtscsi_handle_event, so that all the events are processed in a
> > synchronized way. With this lock, the panic goes away.
> >
> > Signed-off-by: Fam Zheng <famz@xxxxxxxxxx>
> > ---
> > drivers/scsi/virtio_scsi.c | 6 ++++++
> > 1 file changed, 6 insertions(+)
> >
> > diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c
> > index c52bb5d..7f194d4 100644
> > --- a/drivers/scsi/virtio_scsi.c
> > +++ b/drivers/scsi/virtio_scsi.c
> > @@ -110,6 +110,9 @@ struct virtio_scsi {
> > /* CPU hotplug notifier */
> > struct notifier_block nb;
> >
> > + /* Protect the hotplug/unplug event handling */
> > + struct mutex scan_lock;
> > +
> > /* Protected by event_vq lock */
> > bool stop_events;
> >
> > @@ -377,6 +380,7 @@ static void virtscsi_handle_event(struct work_struct
> > *work)
> > struct virtio_scsi *vscsi = event_node->vscsi;
> > struct virtio_scsi_event *event = &event_node->event;
> >
> > + mutex_lock(&vscsi->scan_lock);
> > if (event->event &
> > cpu_to_virtio32(vscsi->vdev, VIRTIO_SCSI_T_EVENTS_MISSED)) {
> > event->event &= ~cpu_to_virtio32(vscsi->vdev,
> > @@ -397,6 +401,7 @@ static void virtscsi_handle_event(struct work_struct
> > *work)
> > pr_err("Unsupport virtio scsi event %x\n", event->event);
> > }
> > virtscsi_kick_event(vscsi, event_node);
> > + mutex_unlock(&vscsi->scan_lock);
> > }
> >
> > static void virtscsi_complete_event(struct virtio_scsi *vscsi, void *buf)
> > @@ -894,6 +899,7 @@ static int virtscsi_init(struct virtio_device *vdev,
> > const char **names;
> > struct virtqueue **vqs;
> >
> > + mutex_init(&vscsi->scan_lock);
> > num_vqs = vscsi->num_queues + VIRTIO_SCSI_VQ_BASE;
> > vqs = kmalloc(num_vqs * sizeof(struct virtqueue *), GFP_KERNEL);
> > callbacks = kmalloc(num_vqs * sizeof(vq_callback_t *), GFP_KERNEL);
> > --
> > 1.9.3
> >
> >
> > Nice find.
> >
> > This fix does have the effect of serializing all event handling via scan_lock;
> > perhaps you want to instead create a singlethreaded workqueue in virtio_scsi
> > and queue handle_event there, rather than waiting on scan_lock on the system
> > workqueue?
>
> Or use the system single-threaded wq.
Good idea, I'll change to that.
Thanks,
Fam
>
>
> > Reviewed-by: Venkatesh Srinivas <venkateshs@xxxxxxxxxx>
> >
> > -- vs;
--
To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
