[PATCH] virtio_balloon: stay awake while adjusting balloon

[David Stevens]

From: David Stevens <steve...@chromium.org>

Add a wakeup event for when the balloon is inflating or deflating.
Userspace can enable this wakeup event to prevent the system from
suspending while the balloon is being adjusted. This allows
/sys/power/wakeup_count to be used without breaking virtio_balloon's
cooperative memory management.

Signed-off-by: David Stevens <steve...@chromium.org>
---
 drivers/virtio/virtio_balloon.c | 59 +++++++++++++++++++++++++++------
 1 file changed, 49 insertions(+), 10 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 1fe93e93f5bc..811d8937246a 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -119,6 +119,11 @@ struct virtio_balloon {
        /* Free page reporting device */
        struct virtqueue *reporting_vq;
        struct page_reporting_dev_info pr_dev_info;
+
+       /* State for keeping the wakeup_source active while adjusting the 
balloon */
+       spinlock_t adjustment_lock;
+       u32 adjustment_seqno;
+       bool adjustment_in_progress;
 };
 
 static const struct virtio_device_id id_table[] = {
@@ -437,6 +442,31 @@ static void virtio_balloon_queue_free_page_work(struct 
virtio_balloon *vb)
        queue_work(vb->balloon_wq, &vb->report_free_page_work);
 }
 
+static void start_update_balloon_size(struct virtio_balloon *vb)
+{
+       unsigned long flags;
+
+       spin_lock_irqsave(&vb->adjustment_lock, flags);
+       vb->adjustment_seqno++;
+       if (!vb->adjustment_in_progress) {
+               vb->adjustment_in_progress = true;
+               pm_stay_awake(&vb->vdev->dev);
+       }
+       spin_unlock_irqrestore(&vb->adjustment_lock, flags);
+
+       queue_work(system_freezable_wq, &vb->update_balloon_size_work);
+}
+
+static void end_update_balloon_size(struct virtio_balloon *vb, u32 seqno)
+{
+       spin_lock(&vb->adjustment_lock);
+       if (vb->adjustment_seqno == seqno && vb->adjustment_in_progress) {
+               vb->adjustment_in_progress = false;
+               pm_relax(&vb->vdev->dev);
+       }
+       spin_unlock(&vb->adjustment_lock);
+}
+
 static void virtballoon_changed(struct virtio_device *vdev)
 {
        struct virtio_balloon *vb = vdev->priv;
@@ -444,8 +474,7 @@ static void virtballoon_changed(struct virtio_device *vdev)
 
        spin_lock_irqsave(&vb->stop_update_lock, flags);
        if (!vb->stop_update) {
-               queue_work(system_freezable_wq,
-                          &vb->update_balloon_size_work);
+               start_update_balloon_size(vb);
                virtio_balloon_queue_free_page_work(vb);
        }
        spin_unlock_irqrestore(&vb->stop_update_lock, flags);
@@ -473,22 +502,29 @@ static void update_balloon_size_func(struct work_struct 
*work)
 {
        struct virtio_balloon *vb;
        s64 diff;
+       u32 seqno;
 
        vb = container_of(work, struct virtio_balloon,
                          update_balloon_size_work);
-       diff = towards_target(vb);
 
-       if (!diff)
-               return;
+       spin_lock(&vb->adjustment_lock);
+       seqno = vb->adjustment_seqno;
+       spin_unlock(&vb->adjustment_lock);
 
-       if (diff > 0)
-               diff -= fill_balloon(vb, diff);
-       else
-               diff += leak_balloon(vb, -diff);
-       update_balloon_size(vb);
+       diff = towards_target(vb);
+
+       if (diff) {
+               if (diff > 0)
+                       diff -= fill_balloon(vb, diff);
+               else
+                       diff += leak_balloon(vb, -diff);
+               update_balloon_size(vb);
+       }
 
        if (diff)
                queue_work(system_freezable_wq, work);
+       else
+               end_update_balloon_size(vb, seqno);
 }
 
 static int init_vqs(struct virtio_balloon *vb)
@@ -992,6 +1028,9 @@ static int virtballoon_probe(struct virtio_device *vdev)
                        goto out_unregister_oom;
        }
 
+       spin_lock_init(&vb->adjustment_lock);
+       device_set_wakeup_capable(&vb->vdev->dev, true);
+
        virtio_device_ready(vdev);
 
        if (towards_target(vb))
-- 
2.43.0.472.g3155946c3a-goog