From: Stefan Hajnoczi <stefanha@redhat.com>
To: "Philippe Mathieu-Daudé" <philmd@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>,
qemu-block@nongnu.org, Xujun Ma <xuma@redhat.com>,
qemu-devel@nongnu.org, Max Reitz <mreitz@redhat.com>,
Yihuang Yu <yihyu@redhat.com>
Subject: Re: [Qemu-devel] [PATCH] virtio-blk: Cancel the pending BH when the dataplane is reset
Date: Thu, 22 Aug 2019 14:01:21 +0100 [thread overview]
Message-ID: <20190822130121.GF20491@stefanha-x1.localdomain> (raw)
In-Reply-To: <20190816171503.24761-1-philmd@redhat.com>
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On Fri, Aug 16, 2019 at 07:15:03PM +0200, Philippe Mathieu-Daudé wrote:
> 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.
>
> 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>
> ---
> hw/block/dataplane/virtio-blk.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
> index 9299a1a7c2..4030faa21d 100644
> --- a/hw/block/dataplane/virtio-blk.c
> +++ b/hw/block/dataplane/virtio-blk.c
> @@ -301,6 +301,8 @@ void virtio_blk_data_plane_stop(VirtIODevice *vdev)
> /* Clean up guest notifier (irq) */
> k->set_guest_notifiers(qbus->parent, nvqs, false);
>
> + qemu_bh_cancel(s->bh);
> +
> vblk->dataplane_started = false;
> s->stopping = false;
> }
> --
> 2.20.1
>
Along the lines of what John said:
diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
index 9299a1a7c2..4030faa21d 100644
--- a/hw/block/dataplane/virtio-blk.c
+++ b/hw/block/dataplane/virtio-blk.c
@@ -301,6 +301,8 @@ void virtio_blk_data_plane_stop(VirtIODevice *vdev)
+ 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);
vblk->dataplane_started = false;
s->stopping = false;
}
Let's notify the guest if any batched notifications are waiting. This
ensures that no notifications are lost when dataplane is stopped.
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next prev parent reply other threads:[~2019-08-22 13:03 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-16 17:15 [Qemu-devel] [PATCH] virtio-blk: Cancel the pending BH when the dataplane is reset Philippe Mathieu-Daudé
2019-08-16 18:35 ` [Qemu-devel] [Qemu-block] " John Snow
2019-08-22 13:03 ` Stefan Hajnoczi
2019-08-22 13:01 ` Stefan Hajnoczi [this message]
2019-08-22 14:56 ` [Qemu-devel] " Philippe Mathieu-Daudé
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