Re: [PATCH v2 2/2] virtio_balloon: avoid shrinker execution during PM suspend

["David Hildenbrand (Arm)" <david@kernel.org>]

On 7/17/26 02:22, Link Lin wrote:
> During PM freeze (e.g. S4 hibernation), virtballoon_freeze() calls
> remove_common() which resets the virtio device and deletes all virtqueues.
> However, the balloon shrinker remains registered with core MM.
> 
> If memory pressure occurs during S4 hibernation image creation/saving, MM
> invokes virtio_balloon_shrinker_scan(), which attempts to reclaim free
> pages. Although return_free_pages_to_mm() only frees pages back to MM,
> reclaiming free pages under memory pressure can trigger page reporting
> which might access the deleted reporting virtqueue if it is not yet
> frozen, or interact with other parts of the driver in a teardown state.

Yes, this does seem possible.

> +
>  static void virtio_balloon_queue_free_page_work(struct virtio_balloon *vb)
>  {
>  	if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
> @@ -871,6 +887,9 @@ static unsigned long virtio_balloon_shrinker_scan(struct shrinker *shrinker,
>  {
>  	struct virtio_balloon *vb = shrinker->private_data;
>  
> +	if (READ_ONCE(vb->suspended))
> +		return 0;
> +
>  	return shrink_free_pages(vb, sc->nr_to_scan);
>  }
>  
> @@ -879,6 +898,9 @@ static unsigned long virtio_balloon_shrinker_count(struct shrinker *shrinker,
>  {
>  	struct virtio_balloon *vb = shrinker->private_data;
>  
> +	if (READ_ONCE(vb->suspended))
> +		return 0;
> +
>  	return vb->num_free_page_blocks * VIRTIO_BALLOON_HINT_BLOCK_PAGES;
>  }
>  
> @@ -1089,8 +1111,11 @@ static void remove_common(struct virtio_balloon *vb)
>  	update_balloon_size(vb);
>  
>  	/* There might be free pages that are being reported: release them. */
> -	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
> -		return_free_pages_to_mm(vb, ULONG_MAX);
> +	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
> +		spin_lock_irq(&vb->free_page_list_lock);
> +		__return_free_pages_to_mm(vb, ULONG_MAX);
> +		spin_unlock_irq(&vb->free_page_list_lock);
> +	}

Why not set the boolean immediately after this, and call it "shrinker_disabled"
instead of "suspended"?

Then you can keep calling "return_free_pages_to_mm(vb, ULONG_MAX);" here.



-- 
Cheers,

David