Re: [Qemu-devel] [PATCH 5/8] virtio-blk: fix "disabled data plane" mode

[Christian Borntraeger]

On 03/09/2016 01:55 PM, Paolo Bonzini wrote:
> 
> 
> On 09/03/2016 13:21, Christian Borntraeger wrote:
>> I have some random crashes at startup 
>>                 
>>                 Stack trace of thread 48326:
>>                 #0  0x000002aa2e0cce46 bdrv_co_do_rw (qemu-system-s390x)
>>                 #1  0x000002aa2e159e8e coroutine_trampoline 
>> (qemu-system-s390x)
>>                 #2  0x000003ffbc35150a __makecontext_ret (libc.so.6)
>>
>>
>> that I was able to bisect.
>> commit 2906cddfecff21af20eedab43288b485a679f9ac does crash regularly, 
>> 2906cddfecff21af20eedab43288b485a679f9ac^ does not.
>>
>> I will try to find somebody that looks into that - unless you have an idea.
> 
> The only random idea is to move
> 
>     vblk->dataplane_started = true
> 
> to the beginning of virtio_blk_data_plane_start rather than the end.
> 
> Paolo
> 

Indeed

diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
index 36f3d2b..1908d59 100644
--- a/hw/block/dataplane/virtio-blk.c
+++ b/hw/block/dataplane/virtio-blk.c
@@ -195,6 +195,7 @@ void virtio_blk_data_plane_start(VirtIOBlockDataPlane *s)
     if (vblk->dataplane_started || s->starting) {
         return;
     }
+    vblk->dataplane_started = true;
 
     s->starting = true;
     s->vq = virtio_get_queue(s->vdev, 0);
@@ -235,7 +236,6 @@ void virtio_blk_data_plane_start(VirtIOBlockDataPlane *s)
   fail_guest_notifiers:
     s->disabled = true;
     s->starting = false;
-    vblk->dataplane_started = true;
 }
 
 /* Context: QEMU global mutex held */

seems to fix the issue.