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

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Date:	Fri, 11 Dec 2015 07:33:11 +0000
From:	Dexuan Cui <decui@...rosoft.com>
To:	KY Srinivasan <kys@...rosoft.com>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"apw@...onical.com" <apw@...onical.com>,
	"vkuznets@...hat.com" <vkuznets@...hat.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>
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)

> > 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,
-- Dexuan

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