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dataplane: avoid reentrancy during virtio_blk_data_plane_stop()

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When dataplane is stopping, the s->vdev->binding->set_host_notifier(...,
false) call can invoke the virtqueue handler if an ioeventfd
notification is pending.  This causes hw/virtio-blk.c to invoke
virtio_blk_data_plane_start() before virtio_blk_data_plane_stop()
returns!

The result is that we try to restart dataplane while trying to stop it
and the following assertion is raised:

  msix_set_mask_notifier: Assertion `!dev->msix_mask_notifier' failed.

Although the code was intended to prevent this scenario, the s->started
boolean isn't enough.  Add s->stopping so that we can postpone clearing
s->started until we've completely stopped dataplane.

This way, virtqueue handler calls during virtio_blk_data_plane_stop()
are ignored.  When dataplane is legitimately started again later we
already self-kick ourselves to resume processing.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2013-01-15 17:19:38 +01:00
parent 3249dbe661
commit cd7fdfe59f
1 changed files with 6 additions and 3 deletions
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9
hw/dataplane/virtio-blk.c
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@ -40,6 +40,7 @@ typedef struct {
struct VirtIOBlockDataPlane {
bool started;
bool stopping;
QEMUBH *start_bh;
QemuThread thread;
@ -357,7 +358,7 @@ static void *data_plane_thread(void *opaque)
do {
event_poll(&s->event_poll);
} while (s->started || s->num_reqs > 0);
} while (!s->stopping || s->num_reqs > 0);
return NULL;
}
@ -486,10 +487,10 @@ void virtio_blk_data_plane_start(VirtIOBlockDataPlane *s)
void virtio_blk_data_plane_stop(VirtIOBlockDataPlane *s)
{
if (!s->started) {
if (!s->started || s->stopping) {
return;
}
s->started = false;
s->stopping = true;
trace_virtio_blk_data_plane_stop(s);
/* Stop thread or cancel pending thread creation BH */
@ -511,4 +512,6 @@ void virtio_blk_data_plane_stop(VirtIOBlockDataPlane *s)
s->vdev->binding->set_guest_notifiers(s->vdev->binding_opaque, 1, false);
vring_teardown(&s->vring);
s->started = false;
s->stopping = false;
}