linux-kernel - RE: [PATCH] Drivers: hv: vmbus: finally fix hv_need_to_signal_on

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Date:   Thu, 26 Jan 2017 06:10:19 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     Stephen Hemminger <stephen@...workplumber.org>
CC:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "driverdev-devel@...uxdriverproject.org" 
        <driverdev-devel@...uxdriverproject.org>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "olaf@...fle.de" <olaf@...fle.de>,
        Rolf Neugebauer <rolf.neugebauer@...ker.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "apw@...onical.com" <apw@...onical.com>
Subject: RE: [PATCH] Drivers: hv: vmbus: finally fix
 hv_need_to_signal_on_read()

> From: Stephen Hemminger [mailto:stephen@...workplumber.org]
> Sent: Wednesday, January 25, 2017 00:08
> To: Dexuan Cui <decui@...rosoft.com>
> Cc: gregkh@...uxfoundation.org; driverdev-devel@...uxdriverproject.org; KY
> Srinivasan <kys@...rosoft.com>; Haiyang Zhang <haiyangz@...rosoft.com>;
> Stephen Hemminger <sthemmin@...rosoft.com>; olaf@...fle.de; Rolf
> Neugebauer <rolf.neugebauer@...ker.com>; jasowang@...hat.com; linux-
> kernel@...r.kernel.org; apw@...onical.com
> Subject: Re: [PATCH] Drivers: hv: vmbus: finally fix hv_need_to_signal_on_read()
> 
> On Tue, 24 Jan 2017 06:54:46 +0000
> Dexuan Cui <decui@...rosoft.com> wrote:
> 
> > +static inline void
> > +init_cached_read_index(struct vmbus_channel *channel)
> > +{
> > +	struct hv_ring_buffer_info *rbi = &channel->inbound;
> > +
> > +	rbi->cached_read_index = rbi->ring_buffer->read_index;
> > +}
> 
> Looks good thanks. This should go in right away. Which versions are impacted?
> Should it also go to stable?

Yes, it needs to go to stable.
I have Cc-ed  <stable@...r.kernel.org> in the patch's changelog, so it should be
included in the stable tree automatically.

As I checked against the kernels listed on the homapage of www.kernel.org, the
below versions are impacted:
v3.16.39
v3.18.47
v4.1.38
v4.8.17
v4.9.5
v4.10-rc5

It's interesting v4.4.44 is not impacted, but actually it needs both the 2 patches:
i.e. this patch, and the previous one:
Commit a389fcfd2cb5 ("Drivers: hv: vmbus: Fix signaling logic in hv_need_to_signal_on_read()")

> In a future patch, the API function names for interacting with the ring buffer
> should be changed to all have common prefix (hv_) and maybe do a little
> rethinking  about what needs to be in ring buffer and what could be local variables.
> 
> For example, the cached_read_index is only useful over the span of the loop
> reading from the ring buffer. For me, it would be cleaner with a ring_buffer
> iterator object which could abstract the API better.
> 
> 	struct vmbus_ringbuffer_iter iter;
> 
> 	vmbus_begin_read(&iter, channel);
> 	while ((desc = vmbus_next_read(&iter), channel) {
> 	    ...
> 	}
> 	vmbus_end_read(&iter, channel);

I agree. Please help to clean all these up.  :-)

Thanks,
-- Dexuan