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Re: [Qemu-devel] [PATCH] vhost: fix crash on virtio_error while device s
From: |
Ilya Maximets |
Subject: |
Re: [Qemu-devel] [PATCH] vhost: fix crash on virtio_error while device stop |
Date: |
Thu, 07 Dec 2017 09:39:36 +0300 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 |
On 06.12.2017 19:45, Michael S. Tsirkin wrote:
> On Wed, Dec 06, 2017 at 04:06:18PM +0300, Ilya Maximets wrote:
>> In case virtio error occured after vhost_dev_close(), qemu will crash
>> in nested cleanup while checking IOMMU flag because dev->vdev already
>> set to zero and resources are already freed.
>>
>> Example:
>>
>> Program received signal SIGSEGV, Segmentation fault.
>> vhost_virtqueue_stop at hw/virtio/vhost.c:1155
>>
>> #0 vhost_virtqueue_stop at hw/virtio/vhost.c:1155
>> #1 vhost_dev_stop at hw/virtio/vhost.c:1594
>> #2 vhost_net_stop_one at hw/net/vhost_net.c:289
>> #3 vhost_net_stop at hw/net/vhost_net.c:368
>>
>> Nested call to vhost_net_stop(). First time was at #14.
>>
>> #4 virtio_net_vhost_status at hw/net/virtio-net.c:180
>> #5 virtio_net_set_status (status=79) at hw/net/virtio-net.c:254
>> #6 virtio_set_status at hw/virtio/virtio.c:1146
>> #7 virtio_error at hw/virtio/virtio.c:2455
>>
>> virtqueue_get_head() failed here.
>>
>> #8 virtqueue_get_head at hw/virtio/virtio.c:543
>> #9 virtqueue_drop_all at hw/virtio/virtio.c:984
>> #10 virtio_net_drop_tx_queue_data at hw/net/virtio-net.c:240
>> #11 virtio_bus_set_host_notifier at hw/virtio/virtio-bus.c:297
>> #12 vhost_dev_disable_notifiers at hw/virtio/vhost.c:1431
>>
>> vhost_dev_stop() was executed here. dev->vdev == NULL now.
>>
>> #13 vhost_net_stop_one at hw/net/vhost_net.c:290
>> #14 vhost_net_stop at hw/net/vhost_net.c:368
>> #15 virtio_net_vhost_status at hw/net/virtio-net.c:180
>> #16 virtio_net_set_status (status=15) at hw/net/virtio-net.c:254
>> #17 qmp_set_link ("hostnet0", up=false) at net/net.c:1430
>> #18 chr_closed_bh at net/vhost-user.c:214
>> #19 aio_bh_call at util/async.c:90
>> #20 aio_bh_poll at util/async.c:118
>> #21 aio_dispatch at util/aio-posix.c:429
>> #22 aio_ctx_dispatch at util/async.c:261
>> #23 g_main_context_dispatch
>> #24 glib_pollfds_poll at util/main-loop.c:213
>> #25 os_host_main_loop_wait at util/main-loop.c:261
>> #26 main_loop_wait at util/main-loop.c:515
>> #27 main_loop () at vl.c:1917
>> #28 main at vl.c:4795
>>
>> Above backtrace captured from qemu crash on vhost disconnect while
>> virtio driver in guest was in failed state.
>>
>> We can just add checking for 'vdev' in 'vhost_dev_has_iommu()' but
>> it will assert further trying to free already freed ioeventfds. The
>> real problem is that we're allowing nested calls to 'vhost_net_stop'.
>>
>> This patch is aimed to forbid nested calls to 'vhost_net_stop' to avoid
>> any possible double frees and segmentation faults doue to using of
>> already freed resources by setting 'vhost_started' flag to zero prior
>> to 'vhost_net_stop' call.
>>
>> Signed-off-by: Ilya Maximets <address@hidden>
>> ---
>>
>> This issue was already addressed more than a year ago by the following
>> patch: https://lists.gnu.org/archive/html/qemu-devel/2016-03/msg06732.html
>> but it was dropped without review due to not yet implemented re-connection
>> of vhost-user. Re-connection implementation lately fixed most of the
>> nested calls, but few of them still exists. For example, above backtrace
>> captured after 'virtqueue_get_head()' failure on vhost-user disconnection.
>>
>> hw/net/virtio-net.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
>> index 38674b0..4d95a18 100644
>> --- a/hw/net/virtio-net.c
>> +++ b/hw/net/virtio-net.c
>> @@ -177,8 +177,8 @@ static void virtio_net_vhost_status(VirtIONet *n,
>> uint8_t status)
>> n->vhost_started = 0;
>> }
>> } else {
>> - vhost_net_stop(vdev, n->nic->ncs, queues);
>> n->vhost_started = 0;
>> + vhost_net_stop(vdev, n->nic->ncs, queues);
>> }
>> }
>
> Well the wider context is
>
>
> n->vhost_started = 1;
> r = vhost_net_start(vdev, n->nic->ncs, queues);
> if (r < 0) {
> error_report("unable to start vhost net: %d: "
> "falling back on userspace virtio", -r);
> n->vhost_started = 0;
> }
> } else {
> vhost_net_stop(vdev, n->nic->ncs, queues);
> n->vhost_started = 0;
>
> So we set it to 1 before start, we should clear after stop.
OK. I agree that clearing after is a bit safer. But in this case we need
a separate flag or other way to detect that we're already inside the
'vhost_net_stop()'.
What do you think about that old patch:
https://lists.gnu.org/archive/html/qemu-devel/2016-03/msg06732.html ?
It implements the same thing but introduces additional flag. It even could
be still applicable.
- [Qemu-devel] [PATCH] vhost: fix crash on virtio_error while device stop, Ilya Maximets, 2017/12/06
- Re: [Qemu-devel] [PATCH] vhost: fix crash on virtio_error while device stop, Michael S. Tsirkin, 2017/12/06
- Re: [Qemu-devel] [PATCH] vhost: fix crash on virtio_error while device stop,
Ilya Maximets <=
- Re: [Qemu-devel] [PATCH] vhost: fix crash on virtio_error while device stop, Michael S. Tsirkin, 2017/12/07
- Re: [Qemu-devel] [PATCH] vhost: fix crash on virtio_error while device stop, Michael S. Tsirkin, 2017/12/07
- Re: [Qemu-devel] [PATCH] vhost: fix crash on virtio_error while device stop, Ilya Maximets, 2017/12/08
- Re: [Qemu-devel] [PATCH] vhost: fix crash on virtio_error while device stop, Michael S. Tsirkin, 2017/12/10
- Re: [Qemu-devel] [PATCH] vhost: fix crash on virtio_error while device stop, Ilya Maximets, 2017/12/13
- Re: [Qemu-devel] [PATCH] vhost: fix crash on virtio_error while device stop, Michael S. Tsirkin, 2017/12/13
- Re: [Qemu-devel] [PATCH] vhost: fix crash on virtio_error while device stop, Ilya Maximets, 2017/12/14
- Re: [Qemu-devel] [PATCH] vhost: fix crash on virtio_error while device stop, Maxime Coquelin, 2017/12/14
- Re: [Qemu-devel] [PATCH] vhost: fix crash on virtio_error while device stop, Ilya Maximets, 2017/12/14
- Re: [Qemu-devel] [PATCH] vhost: fix crash on virtio_error while device stop, Ilya Maximets, 2017/12/14