Re: [Qemu-devel] [PATCH 0/4] Tweaks around virtio-blk start/stop

[Fam Zheng]

On Thu, 03/17 19:03, tu bo wrote:
> 
> On 03/17/2016 08:39 AM, Fam Zheng wrote:
> >On Wed, 03/16 14:45, Paolo Bonzini wrote:
> >>
> >>
> >>On 16/03/2016 14:38, Christian Borntraeger wrote:
> >>>>If you just remove the calls to virtio_queue_host_notifier_read, here
> >>>>and in virtio_queue_aio_set_host_notifier_fd_handler, does it work
> >>>>(keeping patches 2-4 in)?
> >>>
> >>>With these changes and patch 2-4 it does no longer locks up.
> >>>I keep it running some hour to check if a crash happens.
> >>>
> >>>Tu Bo, your setup is currently better suited for reproducing. Can you also 
> >>>check?
> >>
> >>Great, I'll prepare a patch to virtio then sketching the solution that
> >>Conny agreed with.
> >>
> >>While Fam and I agreed that patch 1 is not required, I'm not sure if the
> >>mutex is necessary in the end.
> >
> >If we can fix this from the virtio_queue_host_notifier_read side, the 
> >mutex/BH
> >are not necessary; but OTOH the mutex does catch such bugs, so maybe it's 
> >good
> >to have it. I'm not sure about the BH.
> >
> >And on a hindsight I realize we don't want patches 2-3 too. Actually the
> >begin/end pair won't work as expected because of the blk_set_aio_context.
> >
> >Let's hold on this series.
> >
> >>
> >>So if Tu Bo can check without the virtio_queue_host_notifier_read calls,
> >>and both with/without Fam's patches, it would be great.
> >
> >Tu Bo, only with/withoug patch 4, if you want to check. Sorry for the noise.
> >
> 1. without the virtio_queue_host_notifier_read calls,  without patch 4
> 
> crash happens very often,
> 
> (gdb) bt
> #0  bdrv_co_do_rw (opaque=0x0) at block/io.c:2172
> #1  0x000002aa165da37e in coroutine_trampoline (i0=<optimized out>,
> i1=1812051552) at util/coroutine-ucontext.c:79
> #2  0x000003ff7dd5150a in __makecontext_ret () from /lib64/libc.so.6
> 
> 
> 2. without the virtio_queue_host_notifier_read calls, with patch 4
> 
> crash happens very often,
> 
> (gdb) bt
> #0  bdrv_co_do_rw (opaque=0x0) at block/io.c:2172
> #1  0x000002aa39dda43e in coroutine_trampoline (i0=<optimized out>,
> i1=-1677715600) at util/coroutine-ucontext.c:79
> #2  0x000003ffab6d150a in __makecontext_ret () from /lib64/libc.so.6
> 
> 

Tu Bo,

Could you help test this patch (on top of master, without patch 4)?

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 08275a9..47f8043 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -1098,7 +1098,14 @@ void virtio_queue_notify_vq(VirtQueue *vq)
 
 void virtio_queue_notify(VirtIODevice *vdev, int n)
 {
-    virtio_queue_notify_vq(&vdev->vq[n]);
+    VirtQueue *vq = &vdev->vq[n];
+    EventNotifier *n;
+    n = virtio_queue_get_host_notifier(vq);
+    if (n) {
+        event_notifier_set(n);
+    } else {
+        virtio_queue_notify_vq(vq);
+    }
 }
 
 uint16_t virtio_queue_vector(VirtIODevice *vdev, int n)