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Date: Thu, 14 Mar 2019 18:33:29 +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 17:40, 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@...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? > > 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. Hm, so it does work for your use-case, but doesn't for mine. What would be the best way forward? 1. Implement .resume properly as, for example, block front does [1] 2. Remove .resume completely: this does work as long as backend doesn't change anything I am still a bit unsure if we really need to re-initialize rings, re-read front's config from Xenstore etc - what changes on backend side are expected when we resume the front driver? > > > -boris Thank you, Oleksandr [1] https://elixir.bootlin.com/linux/v5.0.2/source/drivers/block/xen-blkfront.c#L2072
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