netdev - Re: [Xen-devel][PATCH] xen/netfront: Remove unneeded .resume callback

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Date:   Thu, 14 Mar 2019 17:10:14 +0200
From:   Oleksandr Andrushchenko <andr2000@...il.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        netdev@...r.kernel.org, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org, jgross@...e.com,
        sstabellini@...nel.org, davem@...emloft.net
Cc:     Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>,
        Volodymyr Babchuk <Volodymyr_Babchuk@...m.com>
Subject: Re: [Xen-devel][PATCH] xen/netfront: Remove unneeded .resume callback

On 3/14/19 5:02 PM, Boris Ostrovsky wrote:
> On 3/14/19 10:52 AM, Oleksandr Andrushchenko wrote:
>> On 3/14/19 4:47 PM, Boris Ostrovsky wrote:
>>> On 3/14/19 9:17 AM, Oleksandr Andrushchenko wrote:
>>>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>
>>>>
>>>> Currently on driver resume we remove all the network queues and
>>>> destroy shared Tx/Rx rings leaving the driver in its current state
>>>> and never signaling the backend of this frontend's state change.
>>>> This leads to the number of consequences:
>>>> - when frontend withdraws granted references to the rings etc. it
>>>> cannot
>>>>     be cleanly done as the backend still holds those (it was not told to
>>>>     free the resources)
>>>> - it is not possible to resume driver operation as all the
>>>> communication
>>>>     means with the backned were destroyed by the frontend, thus
>>>>     making the frontend appear to the guest OS as functional, but
>>>>     not really.
>>> What do you mean? Are you saying that after resume you lose
>>> connectivity?
>> Exactly, if you take a look at the .resume callback as it is now
>> what it does it destroys the rings etc. and never notifies the backend
>> of that, e.g. it stays in, say, connected state with communication
>> channels destroyed. It never goes into any other Xen bus state, so
>> there is
>> no way its state machine can help recovering.
>
> My tree is about a month old so perhaps there is some sort of regression
> but this certainly works for me. After resume netfront gets
> XenbusStateInitWait from backend which causes xennet_connect().
Ah, the difference can be of the way we get the guest enter
the suspend state. I am making my guest to suspend with:
echo mem > /sys/power/state
And then I use an interrupt to the guest (this is a test code)
to wake it up.
Could you please share your exact use-case when the guest enters suspend
and what you do to resume it?
I can see no way backend may want enter XenbusStateInitWait in my use-case
as it simply doesn't know we want him to.
>
> -boris
>
>
Thank you,
Oleksandr