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

[Dexuan Cui]

> -----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
> --- Begin Message ---
> I found this by chance. I don't have a specific bug caused by this.
>
> Cc: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> Cc: "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx>
> Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> ---
>  tools/hv/hv_vss_daemon.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/hv/hv_vss_daemon.c b/tools/hv/hv_vss_daemon.c
> index 96234b6..5d51d6f 100644
> --- a/tools/hv/hv_vss_daemon.c
> +++ b/tools/hv/hv_vss_daemon.c
> @@ -254,7 +254,7 @@ int main(int argc, char *argv[])
>                         syslog(LOG_ERR, "Illegal op:%d\n", op);
>                 }
>                 vss_msg->error = error;
> -               len = write(vss_fd, &error, sizeof(struct hv_vss_msg));
> +               len = write(vss_fd, vss_msg, sizeof(struct hv_vss_msg));
>                 if (len != sizeof(struct hv_vss_msg)) {
>                         syslog(LOG_ERR, "write failed; error: %d %s", errno,
>                                strerror(errno));
> --
> 1.9.1
>
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> --- End Message ---