From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wei Wang Subject: Re: Re: [PATCH v1 1/2] virtio-balloon: tweak config_changed implementation Date: Fri, 04 Jan 2019 13:14:27 +0800 Message-ID: <5C2EEBB3.3070109@intel.com> References: <1546493462-32244-1-git-send-email-wei.w.wang@intel.com> <1546493462-32244-2-git-send-email-wei.w.wang@intel.com> <20190103113228-mutt-send-email-mst@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Cc: virtio-dev@lists.oasis-open.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, cohuck@redhat.com, borntraeger@de.ibm.com, pbonzini@redhat.com, dgilbert@redhat.com, pasic@linux.ibm.com To: "Michael S. Tsirkin" Return-path: Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: In-Reply-To: <20190103113228-mutt-send-email-mst@kernel.org> List-Id: kvm.vger.kernel.org On 01/04/2019 12:42 AM, Michael S. Tsirkin wrote: > On Thu, Jan 03, 2019 at 01:31:01PM +0800, Wei Wang wrote: >> virtio-ccw has deadlock issues with reading config registers inside the >> interrupt context, so we tweak the virtballoon_changed implementation >> by moving the config read operations into the related workqueue contexts. >> >> Signed-off-by: Wei Wang >> --- >> drivers/virtio/virtio_balloon.c | 54 ++++++++++++++++++++--------------------- >> 1 file changed, 26 insertions(+), 28 deletions(-) >> >> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c >> index 728ecd1..9a82a11 100644 >> --- a/drivers/virtio/virtio_balloon.c >> +++ b/drivers/virtio/virtio_balloon.c >> @@ -394,33 +394,15 @@ static void virtballoon_changed(struct virtio_device *vdev) >> { >> struct virtio_balloon *vb = vdev->priv; >> unsigned long flags; >> - s64 diff = towards_target(vb); >> - >> - if (diff) { >> - spin_lock_irqsave(&vb->stop_update_lock, flags); >> - if (!vb->stop_update) >> - queue_work(system_freezable_wq, >> - &vb->update_balloon_size_work); >> - spin_unlock_irqrestore(&vb->stop_update_lock, flags); >> - } >> >> - if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) { >> - virtio_cread(vdev, struct virtio_balloon_config, >> - free_page_report_cmd_id, &vb->cmd_id_received); > There's one problem with this approach: > > previously updating the cmd_id_received here would immediately > stop the report in send_free_pages. > > With this approach we are waiting for the wq to schedule, > which might be blocked waiting for report to complete. > So host can no longer quickly stop the report in progress. > > A simple work-around would be to set some kind of flag whenever there > is a change interrupt, then have send_free_pages test it > and re-read cmd_id_received. > > Needs to be an atomic I guess ... > Yes, sounds better..will update the patch. Best, Wei