Re: [Qemu-devel] [PATCH v2] virtio-scsi: Allocate op blocker reason before blocking

[Paolo Bonzini <pbonzini@redhat.com>]

On 27/02/2015 18:11, Max Reitz wrote:
> s->blocker is really only used in hw/scsi/virtio-scsi.c; the only places
> where it is used in hw/scsi/virtio-scsi-dataplane.c is when it is
> allocated and when it is freed. That does not make a whole lot of sense
> (and is actually wrong because this leads to s->blocker potentially
> being NULL when blk_op_block_all() is called in virtio-scsi.c), so move
> the allocation and destruction of s->blocker to the device realization
> and unrealization in virtio-scsi.c, respectively.
> 
> Case in point:
> 
> $ echo -e 'eject drv\nquit' | \
>     x86_64-softmmu/qemu-system-x86_64 \
>         -monitor stdio -machine accel=qtest -display none \
>         -object iothread,id=thr -device virtio-scsi-pci,iothread=thr \
>         -drive if=none,file=test.qcow2,format=qcow2,id=drv \
>         -device scsi-cd,drive=drv
> 
> Without this patch:
> 
> (qemu) eject drv
> [1]    10102 done
>        10103 segmentation fault (core dumped)
> 
> With this patch:
> 
> (qemu) eject drv
> Device 'drv' is busy: block device is in use by data plane
> (qemu) quit
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
> v2:
> - Put the reproducer into the commit message [Markus] and modified its
>   wording to be more fitting of a commit message ("Case in point"
>   instead of the imperative "Try").
> - As noted by Fam on my bdrv_close_all() series, there can be multiple
>   block devices per virtio-scsi bus; therefore, it's wrong to delete the
>   blocker if one of these is unplugged. Instead, just allocate the
>   blocker with the virtio-scsi device itself and free it when the device
>   is unrealized.
> ---
>  hw/scsi/virtio-scsi-dataplane.c | 4 ----
>  hw/scsi/virtio-scsi.c           | 4 ++++
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/scsi/virtio-scsi-dataplane.c b/hw/scsi/virtio-scsi-dataplane.c
> index 03a1e8c..9b775d4 100644
> --- a/hw/scsi/virtio-scsi-dataplane.c
> +++ b/hw/scsi/virtio-scsi-dataplane.c
> @@ -211,8 +211,6 @@ void virtio_scsi_dataplane_start(VirtIOSCSI *s)
>  
>      s->dataplane_starting = true;
>  
> -    assert(!s->blocker);
> -    error_setg(&s->blocker, "block device is in use by data plane");
>      /* Set up guest notifier (irq) */
>      rc = k->set_guest_notifiers(qbus->parent, vs->conf.num_queues + 2, true);
>      if (rc != 0) {
> @@ -279,8 +277,6 @@ void virtio_scsi_dataplane_stop(VirtIOSCSI *s)
>      if (!s->dataplane_started || s->dataplane_stopping) {
>          return;
>      }
> -    error_free(s->blocker);
> -    s->blocker = NULL;
>      s->dataplane_stopping = true;
>      assert(s->ctx == iothread_get_aio_context(vs->conf.iothread));
>  
> diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
> index 9e2c718..9c2a272 100644
> --- a/hw/scsi/virtio-scsi.c
> +++ b/hw/scsi/virtio-scsi.c
> @@ -904,6 +904,8 @@ static void virtio_scsi_device_realize(DeviceState *dev, Error **errp)
>                      virtio_scsi_save, virtio_scsi_load, s);
>      s->migration_state_notifier.notify = virtio_scsi_migration_state_changed;
>      add_migration_state_change_notifier(&s->migration_state_notifier);
> +
> +    error_setg(&s->blocker, "block device is in use by data plane");
>  }
>  
>  static void virtio_scsi_instance_init(Object *obj)
> @@ -929,6 +931,8 @@ static void virtio_scsi_device_unrealize(DeviceState *dev, Error **errp)
>  {
>      VirtIOSCSI *s = VIRTIO_SCSI(dev);
>  
> +    error_free(s->blocker);
> +
>      unregister_savevm(dev, "virtio-scsi", s);
>      remove_migration_state_change_notifier(&s->migration_state_notifier);
>  
> 

Applying, thanks.

Paolo