RE: [PATCH V2 02/10] Drivers: hv: utils: run polling callback always in interrupt context

[KY Srinivasan]

> -----Original Message-----
> From: Dexuan Cui
> Sent: Thursday, December 10, 2015 11:33 PM
> To: KY Srinivasan <kys@xxxxxxxxxxxxx>; gregkh@xxxxxxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; devel@xxxxxxxxxxxxxxxxxxxxxx; olaf@xxxxxxxxx;
> apw@xxxxxxxxxxxxx; vkuznets@xxxxxxxxxx; jasowang@xxxxxxxxxx
> Subject: RE: [PATCH V2 02/10] Drivers: hv: utils: run polling callback always in
> interrupt context
> 
> > -----Original Message-----
> > From: KY Srinivasan
> > Sent: Friday, December 11, 2015 7:23
> > > It looks the patch has not been Greg's tree yet.
> > >
> > > I have 2 questions about the patch:
> > >
> > > 1. hv_poll_channel() is invoked in fcopy_handle_handshake(), but not in
> > > vss_handle_handshake() and kvp_handle_handshake().
> > > Why -- I guess we missed the vss/kvp cases somehow?
> > I will fix this.
> 
> Thanks, KY!
> BTW, I fixed another small issue by https://lkml.org/lkml/2015/12/10/50
> (The mail is attached for your convenience)

I will pick this up.

> 
> > > 2.  With the patch, hv_fcopy_onchannelcallback() can be invoked in the
> > > tasklet (i.e., vmbus_on_event(). NB: local irq is enabled), and in the
> > > hard irq handler(the IPI handler, e.g.,
> > > fcopy_poll_wrapper() -> fcopy_poll_wrapper()).
> > >
> > > Can the former be interrupted by the latter?
> > > e.g., when the callback is running in the tasklet on vCPU0,
> > > fcopy_timeout_func() or fcopy_on_msg() could send the IPI to
> > > vCPU0 from another vCPU.
> >
> > Keep in mind that when the poll function is run, the state will not be
> > HVUTIL_READY. The state will be set to HVUTIL_READY in the IPI
> > handler. So, it is ok if the tasklet is interrupted by the IPI handler.
> >
> > K. Y
> 
> Got it.
> 
> BTW, in fcopy_handle_handshake(), IMO the line
> fcopy_transaction.state = HVUTIL_READY;
> just before
> hv_poll_channel(fcopy_transaction.recv_channel, fcopy_poll_wrapper);
> should be removed? Because in fcopy_poll_wrapper() we always have
> the same line.
> 
> Ditto for kvp/vss.
> 
> Thanks,

I will fix this and resend.

Thanks,

K. Y
> -- Dexuan

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