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? 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