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




Hi,

On 3/14/19 3:40 PM, Boris Ostrovsky wrote:
On 3/14/19 11:10 AM, Oleksandr Andrushchenko wrote:
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@xxxxxxxx>

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?


xl save / xl restore

I can see no way backend may want enter XenbusStateInitWait in my
use-case
as it simply doesn't know we want him to.


Yours looks like ACPI path, I don't know how well it was tested TBH.

I remember a series from amazon [1] that plays around suspend and hibernation. The patch [2] leads me to think that guest triggered suspend/resume does not work properly. It looks like the series has never been fully reviewed. Not sure why...

Anyway, from my understanding this series may solve Oleksandr issue. However, this would only address the common code side. AFAIK Oleksandr is targeting Arm platform. If so, I think this would require more work than this series. Arm code still miss few bits properly suspend/resume arch specific code (see [2]).

I have a branch on my git to track the series. However, they never have been resent after Ian Campbell left Citrix. I would be happy to review them if someone wants to pick them up and repost them.

Cheers,

[1] https://lists.xenproject.org/archives/html/xen-devel/2018-06/msg00823.html

[2] http://xenbits.xen.org/gitweb/?p=people/julieng/linux-arm.git;a=shortlog;h=refs/heads/xen-migration/v2



-boris

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--
Julien Grall