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

[Max Reitz <mreitz@redhat.com>]

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 blk_op_block_all() and
blk_op_unblock_all() in virtio-scsi.c, respectively.

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
Try:

$ 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

What it should do:

QEMU 2.2.50 monitor - type 'help' for more information
(qemu) eject drv
Device 'drv' is busy: block device is in use by data plane
(qemu) quit

What it should not do:

QEMU 2.2.50 monitor - type 'help' for more information
(qemu) eject drv
[1]    10102 done
       10103 segmentation fault (core dumped)
---
 hw/scsi/virtio-scsi-dataplane.c | 4 ----
 hw/scsi/virtio-scsi.c           | 6 +++++-
 2 files changed, 5 insertions(+), 5 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..5469bad 100644
--- a/hw/scsi/virtio-scsi.c
+++ b/hw/scsi/virtio-scsi.c
@@ -766,6 +766,8 @@ static void virtio_scsi_hotplug(HotplugHandler *hotplug_dev, DeviceState *dev,
         if (blk_op_is_blocked(sd->conf.blk, BLOCK_OP_TYPE_DATAPLANE, errp)) {
             return;
         }
+        assert(!s->blocker);
+        error_setg(&s->blocker, "block device is in use by data plane");
         blk_op_block_all(sd->conf.blk, s->blocker);
     }
 
@@ -789,8 +791,10 @@ static void virtio_scsi_hotunplug(HotplugHandler *hotplug_dev, DeviceState *dev,
                                VIRTIO_SCSI_EVT_RESET_REMOVED);
     }
 
-    if (s->ctx) {
+    if (s->ctx && s->blocker) {
         blk_op_unblock_all(sd->conf.blk, s->blocker);
+        error_free(s->blocker);
+        s->blocker = NULL;
     }
     qdev_simple_device_unplug_cb(hotplug_dev, dev, errp);
 }
-- 
2.1.0