From: Cornelia Huck <cohuck@redhat.com>
To: Vineeth Vijayan <vneethv@linux.ibm.com>,
Halil Pasic <pasic@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>,
Vasily Gorbik <gor@linux.ibm.com>,
Christian Borntraeger <borntraeger@de.ibm.com>,
Pierre Morel <pmorel@linux.ibm.com>,
Michael Mueller <mimu@linux.ibm.com>,
linux-s390@vger.kernel.org,
virtualization@lists.linux-foundation.org, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org, bfu@redhat.com
Subject: Re: [PATCH 1/1] virtio/s390: fix vritio-ccw device teardown
Date: Mon, 20 Sep 2021 12:07:23 +0200 [thread overview]
Message-ID: <878rzrh86c.fsf@redhat.com> (raw)
In-Reply-To: <88b514a4416cf72cda53a31ad2e15c13586350e4.camel@linux.ibm.com>
On Mon, Sep 20 2021, Vineeth Vijayan <vneethv@linux.ibm.com> wrote:
> On Mon, 2021-09-20 at 00:39 +0200, Halil Pasic wrote:
>> On Fri, 17 Sep 2021 10:40:20 +0200
>> Cornelia Huck <cohuck@redhat.com> wrote:
>>
> ...snip...
>> > >
>> > > Thanks, if I find time for it, I will try to understand this
>> > > better and
>> > > come back with my findings.
>> > >
>> > > > > * Can virtio_ccw_remove() get called while !cdev->online and
>> > > > > virtio_ccw_online() is running on a different cpu? If yes,
>> > > > > what would
>> > > > > happen then?
>> > > >
>> > > > All of the remove/online/... etc. callbacks are invoked via the
>> > > > ccw bus
>> > > > code. We have to trust that it gets it correct :) (Or have the
>> > > > common
>> > > > I/O layer maintainers double-check it.)
>> > > >
>> > >
>> > > Vineeth, what is your take on this? Are the struct ccw_driver
>> > > virtio_ccw_remove and the virtio_ccw_online callbacks mutually
>> > > exclusive. Please notice that we may initiate the onlining by
>> > > calling ccw_device_set_online() from a workqueue.
>> > >
>> > > @Conny: I'm not sure what is your definition of 'it gets it
>> > > correct'...
>> > > I doubt CIO can make things 100% foolproof in this area.
>> >
>> > Not 100% foolproof, but "don't online a device that is in the
>> > progress
>> > of going away" seems pretty basic to me.
>> >
>>
>> I hope Vineeth will chime in on this.
> Considering the online/offline processing,
> The ccw_device_set_offline function or the online/offline is handled
> inside device_lock. Also, the online_store function takes care of
> avoiding multiple online/offline processing.
>
> Now, when we consider the unconditional remove of the device,
> I am not familiar with the virtio_ccw driver. My assumptions are based
> on how CIO/dasd drivers works. If i understand correctly, the dasd
> driver sets different flags to make sure that a device_open is getting
> prevented while the the device is in progress of offline-ing.
Hm, if we are invoking the online/offline callbacks under the device
lock already, how would that affect the remove callback? Shouldn't they
be serialized under the device lock already? I think we are fine.
For dasd, I think they also need to deal with the block device
lifetimes. For virtio-ccw, we are basically a transport that does not
know about devices further down the chain (that are associated with the
virtio device, whose lifetime is tied to online/offline processing.) I'd
presume that the serialization above would be enough.
next prev parent reply other threads:[~2021-09-20 10:07 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-15 21:57 [PATCH 1/1] virtio/s390: fix vritio-ccw device teardown Halil Pasic
2021-09-15 22:00 ` Halil Pasic
2021-09-16 8:59 ` Cornelia Huck
2021-09-16 13:18 ` Halil Pasic
2021-09-17 8:40 ` Cornelia Huck
2021-09-19 22:39 ` Halil Pasic
2021-09-20 7:41 ` Vineeth Vijayan
2021-09-20 10:07 ` Cornelia Huck [this message]
2021-09-21 3:25 ` Halil Pasic
2021-09-21 12:09 ` Cornelia Huck
2021-09-21 13:31 ` Vineeth Vijayan
2021-09-21 16:52 ` Halil Pasic
2021-09-21 18:25 ` Vineeth Vijayan
2021-09-20 10:30 ` Cornelia Huck
2021-09-20 13:27 ` Halil Pasic
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=878rzrh86c.fsf@redhat.com \
--to=cohuck@redhat.com \
--cc=bfu@redhat.com \
--cc=borntraeger@de.ibm.com \
--cc=gor@linux.ibm.com \
--cc=hca@linux.ibm.com \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-s390@vger.kernel.org \
--cc=mimu@linux.ibm.com \
--cc=pasic@linux.ibm.com \
--cc=pmorel@linux.ibm.com \
--cc=virtualization@lists.linux-foundation.org \
--cc=vneethv@linux.ibm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).