On Wed, May 13, 2020 at 11:20:50AM +0800, Jason Wang wrote: > > On 2020/5/12 下午5:35, Dima Stepanov wrote: > >On Tue, May 12, 2020 at 11:32:50AM +0800, Jason Wang wrote: > >>On 2020/5/11 下午5:25, Dima Stepanov wrote: > >>>On Mon, May 11, 2020 at 11:15:53AM +0800, Jason Wang wrote: > >>>>On 2020/4/30 下午9:36, Dima Stepanov wrote: > >>>>>If vhost-user daemon is used as a backend for the vhost device, then we > >>>>>should consider a possibility of disconnect at any moment. If such > >>>>>disconnect happened in the vhost_migration_log() routine the vhost > >>>>>device structure will be clean up. > >>>>>At the start of the vhost_migration_log() function there is a check: > >>>>> if (!dev->started) { > >>>>> dev->log_enabled = enable; > >>>>> return 0; > >>>>> } > >>>>>To be consistent with this check add the same check after calling the > >>>>>vhost_dev_set_log() routine. This in general help not to break a > >>>>>migration due the assert() message. But it looks like that this code > >>>>>should be revised to handle these errors more carefully. > >>>>> > >>>>>In case of vhost-user device backend the fail paths should consider the > >>>>>state of the device. In this case we should skip some function calls > >>>>>during rollback on the error paths, so not to get the NULL dereference > >>>>>errors. > >>>>> > >>>>>Signed-off-by: Dima Stepanov<dimas...@yandex-team.ru> > >>>>>--- > >>>>> hw/virtio/vhost.c | 39 +++++++++++++++++++++++++++++++++++---- > >>>>> 1 file changed, 35 insertions(+), 4 deletions(-) > >>>>> > >>>>>diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c > >>>>>index 3ee50c4..d5ab96d 100644 > >>>>>--- a/hw/virtio/vhost.c > >>>>>+++ b/hw/virtio/vhost.c > >>>>>@@ -787,6 +787,17 @@ static int vhost_dev_set_features(struct vhost_dev > >>>>>*dev, > >>>>> static int vhost_dev_set_log(struct vhost_dev *dev, bool enable_log) > >>>>> { > >>>>> int r, i, idx; > >>>>>+ > >>>>>+ if (!dev->started) { > >>>>>+ /* > >>>>>+ * If vhost-user daemon is used as a backend for the > >>>>>+ * device and the connection is broken, then the vhost_dev > >>>>>+ * structure will be reset all its values to 0. > >>>>>+ * Add additional check for the device state. > >>>>>+ */ > >>>>>+ return -1; > >>>>>+ } > >>>>>+ > >>>>> r = vhost_dev_set_features(dev, enable_log); > >>>>> if (r < 0) { > >>>>> goto err_features; > >>>>>@@ -801,12 +812,19 @@ static int vhost_dev_set_log(struct vhost_dev > >>>>>*dev, bool enable_log) > >>>>> } > >>>>> return 0; > >>>>> err_vq: > >>>>>- for (; i >= 0; --i) { > >>>>>+ /* > >>>>>+ * Disconnect with the vhost-user daemon can lead to the > >>>>>+ * vhost_dev_cleanup() call which will clean up vhost_dev > >>>>>+ * structure. > >>>>>+ */ > >>>>>+ for (; dev->started && (i >= 0); --i) { > >>>>> idx = dev->vhost_ops->vhost_get_vq_index( > >>>>Why need the check of dev->started here, can started be modified outside > >>>>mainloop? If yes, I don't get the check of !dev->started in the beginning > >>>>of > >>>>this function. > >>>> > >>>No dev->started can't change outside the mainloop. The main problem is > >>>only for the vhost_user_blk daemon. Consider the case when we > >>>successfully pass the dev->started check at the beginning of the > >>>function, but after it we hit the disconnect on the next call on the > >>>second or third iteration: > >>> r = vhost_virtqueue_set_addr(dev, dev->vqs + i, idx, enable_log); > >>>The unix socket backend device will call the disconnect routine for this > >>>device and reset the structure. So the structure will be reset (and > >>>dev->started set to false) inside this set_addr() call. > >>I still don't get here. I think the disconnect can not happen in the middle > >>of vhost_dev_set_log() since both of them were running in mainloop. And even > >>if it can, we probably need other synchronization mechanism other than > >>simple check here. > >Disconnect isn't happened in the separate thread it is happened in this > >routine inside vhost_dev_set_log. When for instance vhost_user_write() > >call failed: > > vhost_user_set_log_base() > > vhost_user_write() > > vhost_user_blk_disconnect() > > vhost_dev_cleanup() > > vhost_user_backend_cleanup() > >So the point is that if we somehow got a disconnect with the > >vhost-user-blk daemon before the vhost_user_write() call then it will > >continue clean up by running vhost_user_blk_disconnect() function. I > >wrote a more detailed backtrace stack in the separate thread, which is > >pretty similar to what we have here: > > Re: [PATCH v2 4/5] vhost: check vring address before calling unmap > >The places are different but the problem is pretty similar. > > > Yes. > > > > > >So if vhost-user commands handshake then everything is fine and > >reconnect will work as expected. The only problem is how to handle > >reconnect properly between vhost-user command send/receive. > > > >As i wrote we have a test: > > - run src VM with vhost-usr-blk daemon used > > - run fio inside it > > - perform reconnect every X seconds (just kill and restart daemon), > > X is random > > - run dst VM > > - perform migration > > - fio should complete in dst VM > >And we cycle this test like forever. > >So it fails once per ~25 iteration. By adding some delays inside qemu we > >were able to make the race window larger. > > > It would be better if we can draft some qtest for this. Yes, i'm in process of figuring out how to make/reproduce it in the qtest framework instead of our internal one.
> > Thanks > > > > >