linux-kernel - Re: [PATCH v2 char-misc 1/1] Drivers: hv: vmbus: Fix ring buffer signaling

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Date:   Mon, 26 Feb 2018 16:10:00 -0800
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Michael Kelley <mhkelley@...look.com>
Cc:     "mikelley@...rosoft.com" <mikelley@...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>,
        "leann.ogasawara@...onical.com" <leann.ogasawara@...onical.com>,
        "marcelo.cerri@...onical.com" <marcelo.cerri@...onical.com>,
        "sthemmin@...rosoft.com" <sthemmin@...rosoft.com>,
        "kys@...rosoft.com" <kys@...rosoft.com>
Subject: Re: [PATCH v2 char-misc 1/1] Drivers: hv: vmbus: Fix ring buffer
 signaling

On Fri, 16 Feb 2018 23:05:33 +0000
Michael Kelley <mhkelley@...look.com> wrote:

> Fix bugs in signaling the Hyper-V host when freeing space in the
> host->guest ring buffer:
> 
> 1. The interrupt_mask must not be used to determine whether to signal
>    on the host->guest ring buffer
> 2. The ring buffer write_index must be read (via hv_get_bytes_to_write)
>    *after* pending_send_sz is read in order to avoid a race condition
> 3. Comparisons with pending_send_sz must treat the "equals" case as
>    not-enough-space
> 4. Don't signal if the pending_send_sz feature is not present. Older
>    versions of Hyper-V that don't implement this feature will poll.
> 
> Fixes: 03bad714a161 ("vmbus: more host signalling avoidance")
> Signed-off-by: Michael Kelley <mhkelley@...look.com>

Signed-off-by: Stephen Hemminger <sthemmin@...rosoft.com>