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Mon, 20 Sep 2021 06:07:33 -0400 X-MC-Unique: OvxKwz2wN0ygX4b2jsTIuQ-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 16C8B835DE4; Mon, 20 Sep 2021 10:07:31 +0000 (UTC) Received: from localhost (unknown [10.39.193.92]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C6CFE101E24F; Mon, 20 Sep 2021 10:07:24 +0000 (UTC) From: Cornelia Huck To: Vineeth Vijayan , Halil Pasic Subject: Re: [PATCH 1/1] virtio/s390: fix vritio-ccw device teardown In-Reply-To: <88b514a4416cf72cda53a31ad2e15c13586350e4.camel@linux.ibm.com> Organization: Red Hat GmbH References: <20210915215742.1793314-1-pasic@linux.ibm.com> <87pmt8hp5o.fsf@redhat.com> <20210916151835.4ab512b2.pasic@linux.ibm.com> <87mtobh9xn.fsf@redhat.com> <20210920003935.1369f9fe.pasic@linux.ibm.com> <88b514a4416cf72cda53a31ad2e15c13586350e4.camel@linux.ibm.com> User-Agent: Notmuch/0.32.1 (https://notmuchmail.org) Date: Mon, 20 Sep 2021 12:07:23 +0200 Message-ID: <878rzrh86c.fsf@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Cc: linux-s390@vger.kernel.org, Vasily Gorbik , Pierre Morel , Heiko Carstens , bfu@redhat.com, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Christian Borntraeger , kvm@vger.kernel.org, Michael Mueller X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" On Mon, Sep 20 2021, Vineeth Vijayan wrote: > On Mon, 2021-09-20 at 00:39 +0200, Halil Pasic wrote: >> On Fri, 17 Sep 2021 10:40:20 +0200 >> Cornelia Huck 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. _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization