> From: Michael Kelley <mikelley@xxxxxxxxxxxxx>
> Sent: Wednesday, January 22, 2020 10:28 AM
> ...
> > +int hv_fcopy_pre_suspend(void)
> > +{
> > + struct vmbus_channel *channel = fcopy_transaction.recv_channel;
> > + struct hv_fcopy_hdr *fcopy_msg;
> > +
> > + tasklet_disable(&channel->callback_event);
> > + ...
> > + fcopy_msg = kzalloc(sizeof(*fcopy_msg), GFP_KERNEL);
> > + if (!fcopy_msg)
> > + goto err;
> > +
> > + fcopy_msg->operation = CANCEL_FCOPY;
> > +
> > + hv_fcopy_cancel_work();
> > +
> > + /* We don't care about the return value. */
> > + hvutil_transport_send(hvt, fcopy_msg, sizeof(*fcopy_msg), NULL);
> > +
> > + kfree(fcopy_msg);
> > +
> > + fcopy_transaction.state = HVUTIL_READY;
>
> Is the ordering correct here?
This is intentional. I'll add a comment (please see the below).
> It seems like the fcopy daemon could receive
> the cancel message and do the write before the state is forced to
> HVUTIL_READY.
This can not happen, because when we're here from util_suspend(), all the
userspace processes have been frozen (please refer to another mail from me
https://lkml.org/lkml/2020/1/13/1021). The userspace is thawed only after
util_resume() and the other part of the resume procedure finish.
When we're here in util_suspend(), we can be in any of the below states:
#1: hv_utils has not queued any message to the userspace daemon.
Now hv_fcopy_pre_suspend() queues a message to the daemon, and forces
the state to HVUTIL_READY; the daemon should read the message without
any error; later when the daemon calls write(), the write() returns -1 because
fcopy_transaction.state != HVUTIL_USERSPACE_REQ and fcopy_on_msg()
returns -EINVAL; the daemon responds to the write() error by closing and
re-opening the dev file, which triggers a reset in the hv_utils driver: see
hvt_op_release() -> hvt_reset() -> fcopy_on_reset(), and later the daemon
registers itself to the hv_utils driver, and everything comes back to normal.
#2: hv_utils has queued a message to the userspace daemon.
Now hv_fcopy_pre_suspend() fails to queue an extra message to the
daemon, but still forces the state to HVUTIL_READY.
#2.1 the userspace has not read the message.
The daemon reads the queued message and later the write() fails, so the
daemon closes and re-opens the dev file.
#2.2 the userspace has read the message, but has not called write() yet.
The write() fails, so the daemon closes and re-opens the dev file.
#2.3 the userspace has read the message, and has called write().
This is actualy the same as #1.
So, IMO the patch should be handling the scenarios correctly.
> > +
> > + /* tasklet_enable() will be called in hv_fcopy_pre_resume(). */
> > +
> > + return 0;
> > +err:
> > + tasklet_enable(&channel->callback_event);
>
> A nit, but if you did the memory allocation first, you could return -ENOMEM
> immediately on error and avoid the err: label and re-enabling the tasklet.
Good idea! I'll fix this.
> > + return -ENOMEM;
> > +}
> > ...
> > --- a/drivers/hv/hv_snapshot.c
> > +++ b/drivers/hv/hv_snapshot.c
> > @@ -229,6 +229,7 @@ static void vss_handle_request(struct work_struct
> *dummy)
> > vss_transaction.state = HVUTIL_HOSTMSG_RECEIVED;
> > vss_send_op();
> > return;
> > +
>
> Gratuitous blank line added?
Will remove it. I probably tried to make the "return;" more noticeable.
> > case VSS_OP_GET_DM_INFO:
> > vss_transaction.msg->dm_info.flags = 0;
> > break;
> > ...
> > +int hv_vss_pre_suspend(void)
> > +{
> > ...
> > + /* We don't care about the return value. */
> > + hvutil_transport_send(hvt, vss_msg, sizeof(*vss_msg), NULL);
> > +
> > + kfree(vss_msg);
> > +
> > + vss_transaction.state = HVUTIL_READY;
>
> Same comment about the ordering.
I'll add a comment for this. I may add a long comment in util_suspend()
and add a short comment here.
> > +
> > + /* tasklet_enable() will be called in hv_vss_pre_resume(). */
> > +
> > + return 0;
> > +err:
> > + tasklet_enable(&channel->callback_event);
> > + return -ENOMEM;
>
> Same comment about simplifying the error handling applies here.
Will fix this.
> > +static int util_suspend(struct hv_device *dev)
> > +{
> > + struct hv_util_service *srv = hv_get_drvdata(dev);
> > + int ret = 0;
> > +
> > + if (srv->util_pre_suspend) {
> > + ret = srv->util_pre_suspend();
> > +
>
> Unneeded blank line?
Will remove this.
> > + if (ret)
> > + return ret;
> > + }
> > +
> > + vmbus_close(dev->channel);
> > +
> > + return 0;
> > +}
> > +
> > +static int util_resume(struct hv_device *dev)
> > +{
> > + struct hv_util_service *srv = hv_get_drvdata(dev);
> > + int ret = 0;
> > +
> > + if (srv->util_pre_resume) {
> > + ret = srv->util_pre_resume();
> > +
>
> Unneeded blank line?
Will remove this.
Thanks,
-- Dexuan
