Date: Tue, 6 Dec 2016 11:07:31 +0100
From: Greg KH <gregkh@linuxfoundation.org>
To: kys@microsoft.com
Cc: linux-kernel@vger.kernel.org, devel@linuxdriverproject.org,
        olaf@aepfle.de, apw@canonical.com, vkuznets@redhat.com,
        jasowang@redhat.com, leann.ogasawara@canonical.com
Subject: Re: [PATCH V2 01/15] Drivers: hv: vmbus: Raise retry/wait limits in
 vmbus_post_msg()
Message-ID: <20161206100731.GA32261@kroah.com>
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On Sat, Dec 03, 2016 at 12:34:28PM -0800, kys@exchange.microsoft.com wrote:
> From: Vitaly Kuznetsov <vkuznets@redhat.com>
> 
> DoS protection conditions were altered in WS2016 and now it's easy to get
> -EAGAIN returned from vmbus_post_msg() (e.g. when we try changing MTU on a
> netvsc device in a loop). All vmbus_post_msg() callers don't retry the
> operation and we usually end up with a non-functional device or crash.
> 
> While host's DoS protection conditions are unknown to me my tests show that
> it can take up to 10 seconds before the message is sent so doing udelay()
> is not an option, we really need to sleep. Almost all vmbus_post_msg()
> callers are ready to sleep but there is one special case:
> vmbus_initiate_unload() which can be called from interrupt/NMI context and
> we can't sleep there. I'm also not sure about the lonely
> vmbus_send_tl_connect_request() which has no in-tree users but its external
> users are most likely waiting for the host to reply so sleeping there is
> also appropriate.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>

Shouldn't this go to stable kernels so that 4.9 and earlier can work
properly on WS2016?

thanks,

greg k-h