linux-kernel - [PATCH v2 1/2] virtio_balloon: Give the balloon its own wakeup source

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Date: Thu, 21 Mar 2024 10:24:44 +0900
From: David Stevens <stevensd@...omium.org>
To: "Michael S . Tsirkin" <mst@...hat.com>,
	David Hildenbrand <david@...hat.com>
Cc: virtualization@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org,
	David Stevens <stevensd@...omium.org>
Subject: [PATCH v2 1/2] virtio_balloon: Give the balloon its own wakeup source

From: David Stevens <stevensd@...omium.org>

Wakeup sources don't support nesting multiple events, so sharing a
single object between multiple drivers can result in one driver
overriding the wakeup event processing period specified by another
driver. Have the virtio balloon driver use the wakeup source of the
device it is bound to rather than the wakeup source of the parent
device, to avoid conflicts with the transport layer.

Note that although the virtio balloon's virtio_device itself isn't what
actually wakes up the device, it is responsible for processing wakeup
events. In the same way that EPOLLWAKEUP uses a dedicated wakeup_source
to prevent suspend when userspace is processing wakeup events, a
dedicated wakeup_source is necessary when processing wakeup events in a
higher layer in the kernel.

Fixes: b12fbc3f787e ("virtio_balloon: stay awake while adjusting balloon")
Signed-off-by: David Stevens <stevensd@...omium.org>
Acked-by: David Hildenbrand <david@...hat.com>
---
 drivers/virtio/virtio_balloon.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 1f5b3dd31fcf..89bc8da80519 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -450,7 +450,7 @@ static void start_update_balloon_size(struct virtio_balloon *vb)
 	vb->adjustment_signal_pending = true;
 	if (!vb->adjustment_in_progress) {
 		vb->adjustment_in_progress = true;
-		pm_stay_awake(vb->vdev->dev.parent);
+		pm_stay_awake(&vb->vdev->dev);
 	}
 	spin_unlock_irqrestore(&vb->adjustment_lock, flags);
 
@@ -462,7 +462,7 @@ static void end_update_balloon_size(struct virtio_balloon *vb)
 	spin_lock_irq(&vb->adjustment_lock);
 	if (!vb->adjustment_signal_pending && vb->adjustment_in_progress) {
 		vb->adjustment_in_progress = false;
-		pm_relax(vb->vdev->dev.parent);
+		pm_relax(&vb->vdev->dev);
 	}
 	spin_unlock_irq(&vb->adjustment_lock);
 }
@@ -1029,6 +1029,15 @@ static int virtballoon_probe(struct virtio_device *vdev)
 
 	spin_lock_init(&vb->adjustment_lock);
 
+	/*
+	 * The virtio balloon itself can't wake up the device, but it is
+	 * responsible for processing wakeup events passed up from the transport
+	 * layer. Wakeup sources don't support nesting/chaining calls, so we use
+	 * our own wakeup source to ensure wakeup events are properly handled
+	 * without trampling on the transport layer's wakeup source.
+	 */
+	device_set_wakeup_capable(&vb->vdev->dev, true);
+
 	virtio_device_ready(vdev);
 
 	if (towards_target(vb))
-- 
2.44.0.291.gc1ea87d7ee-goog