[Qemu-devel] [PULL 0/1] Block patches

[Qemu-devel] [PULL 0/1] Block patches

[Stefan Hajnoczi]

The following changes since commit cc6613e244e86c66f83467eab5284825d7057cea:

  Merge remote-tracking branch 'remotes/stefanha/tags/tracing-pull-request' into staging (2019-09-03 11:06:09 +0100)

are available in the Git repository at:

  https://github.com/stefanha/qemu.git tags/block-pull-request

for you to fetch changes up to ebb6ff25cd888a52a64a9adc3692541c6d1d9a42:

  virtio-blk: Cancel the pending BH when the dataplane is reset (2019-09-03 16:11:18 +0100)

----------------------------------------------------------------
Pull request

----------------------------------------------------------------

Philippe Mathieu-Daudé (1):
  virtio-blk: Cancel the pending BH when the dataplane is reset

 hw/block/dataplane/virtio-blk.c | 3 +++
 1 file changed, 3 insertions(+)

-- 
2.21.0

[Qemu-devel] [PULL 1/1] virtio-blk: Cancel the pending BH when the dataplane is reset

[Stefan Hajnoczi]

From: Philippe Mathieu-Daudé <philmd@redhat.com>

When 'system_reset' is called, the main loop clear the memory
region cache before the BH has a chance to execute. Later when
the deferred function is called, some assumptions that were
made when scheduling them are no longer true when they actually
execute.

This is what happens using a virtio-blk device (fresh RHEL7.8 install):

 $ (sleep 12.3; echo system_reset; sleep 12.3; echo system_reset; sleep 1; echo q) \
   | qemu-system-x86_64 -m 4G -smp 8 -boot menu=on \
     -device virtio-blk-pci,id=image1,drive=drive_image1 \
     -drive file=/var/lib/libvirt/images/rhel78.qcow2,if=none,id=drive_image1,format=qcow2,cache=none \
     -device virtio-net-pci,netdev=net0,id=nic0,mac=52:54:00:c4:e7:84 \
     -netdev tap,id=net0,script=/bin/true,downscript=/bin/true,vhost=on \
     -monitor stdio -serial null -nographic
  (qemu) system_reset
  (qemu) system_reset
  (qemu) qemu-system-x86_64: hw/virtio/virtio.c:225: vring_get_region_caches: Assertion `caches != NULL' failed.
  Aborted

  (gdb) bt
  Thread 1 (Thread 0x7f109c17b680 (LWP 10939)):
  #0  0x00005604083296d1 in vring_get_region_caches (vq=0x56040a24bdd0) at hw/virtio/virtio.c:227
  #1  0x000056040832972b in vring_avail_flags (vq=0x56040a24bdd0) at hw/virtio/virtio.c:235
  #2  0x000056040832d13d in virtio_should_notify (vdev=0x56040a240630, vq=0x56040a24bdd0) at hw/virtio/virtio.c:1648
  #3  0x000056040832d1f8 in virtio_notify_irqfd (vdev=0x56040a240630, vq=0x56040a24bdd0) at hw/virtio/virtio.c:1662
  #4  0x00005604082d213d in notify_guest_bh (opaque=0x56040a243ec0) at hw/block/dataplane/virtio-blk.c:75
  #5  0x000056040883dc35 in aio_bh_call (bh=0x56040a243f10) at util/async.c:90
  #6  0x000056040883dccd in aio_bh_poll (ctx=0x560409161980) at util/async.c:118
  #7  0x0000560408842af7 in aio_dispatch (ctx=0x560409161980) at util/aio-posix.c:460
  #8  0x000056040883e068 in aio_ctx_dispatch (source=0x560409161980, callback=0x0, user_data=0x0) at util/async.c:261
  #9  0x00007f10a8fca06d in g_main_context_dispatch () at /lib64/libglib-2.0.so.0
  #10 0x0000560408841445 in glib_pollfds_poll () at util/main-loop.c:215
  #11 0x00005604088414bf in os_host_main_loop_wait (timeout=0) at util/main-loop.c:238
  #12 0x00005604088415c4 in main_loop_wait (nonblocking=0) at util/main-loop.c:514
  #13 0x0000560408416b1e in main_loop () at vl.c:1923
  #14 0x000056040841e0e8 in main (argc=20, argv=0x7ffc2c3f9c58, envp=0x7ffc2c3f9d00) at vl.c:4578

Fix this by cancelling the BH when the virtio dataplane is stopped.

[This is version of the patch was modified as discussed with Philippe on
the mailing list thread.
--Stefan]

Reported-by: Yihuang Yu <yihyu@redhat.com>
Suggested-by: Stefan Hajnoczi <stefanha@redhat.com>
Fixes: https://bugs.launchpad.net/qemu/+bug/1839428
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20190816171503.24761-1-philmd@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 hw/block/dataplane/virtio-blk.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
index 9299a1a7c2..119906a5fe 100644
--- a/hw/block/dataplane/virtio-blk.c
+++ b/hw/block/dataplane/virtio-blk.c
@@ -298,6 +298,9 @@ void virtio_blk_data_plane_stop(VirtIODevice *vdev)
         virtio_bus_cleanup_host_notifier(VIRTIO_BUS(qbus), i);
     }
 
+    qemu_bh_cancel(s->bh);
+    notify_guest_bh(s); /* final chance to notify guest */
+
     /* Clean up guest notifier (irq) */
     k->set_guest_notifiers(qbus->parent, nvqs, false);
 
-- 
2.21.0

Re: [Qemu-devel] [PULL 0/1] Block patches

[Peter Maydell]

On Wed, 11 Sep 2019 at 15:36, Stefan Hajnoczi <stefanha@redhat.com> wrote:
>
> The following changes since commit cc6613e244e86c66f83467eab5284825d7057cea:
>
>   Merge remote-tracking branch 'remotes/stefanha/tags/tracing-pull-request' into staging (2019-09-03 11:06:09 +0100)
>
> are available in the Git repository at:
>
>   https://github.com/stefanha/qemu.git tags/block-pull-request
>
> for you to fetch changes up to ebb6ff25cd888a52a64a9adc3692541c6d1d9a42:
>
>   virtio-blk: Cancel the pending BH when the dataplane is reset (2019-09-03 16:11:18 +0100)
>
> ----------------------------------------------------------------
> Pull request
>
> ----------------------------------------------------------------
>
> Philippe Mathieu-Daudé (1):
>   virtio-blk: Cancel the pending BH when the dataplane is reset
>
>  hw/block/dataplane/virtio-blk.c | 3 +++
>  1 file changed, 3 insertions(+)


Applied, thanks.

Please update the changelog at https://wiki.qemu.org/ChangeLog/4.2
for any user-visible changes.

-- PMM