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

[Link Lin]

On Thu, Jul 16, 2026 at 5:24 PM Link Lin <linkl@xxxxxxxxxx> 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.
>
> Avoid this by adding a `suspended` flag to `struct virtio_balloon`. Set
> this flag to true in virtballoon_freeze() and false in
> virtballoon_restore(). Check this flag in both shrinker callbacks (scan
> and count) and return 0 if the device is suspended, preventing any
> shrinker execution while virtqueues are deleted. Wrap the lockless reads
> in READ_ONCE() and writes in WRITE_ONCE() to prevent compiler
> optimization issues and KCSAN data race warnings.
>
> Fixes: 71019de8219b ("virtio_balloon: Add free page hinting support")
> Cc: stable@xxxxxxxxxxxxxxx
> Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
> Signed-off-by: Link Lin <linkl@xxxxxxxxxx>

Apologies, I missed adding a tag for the feedback that led to the
TOCTOU locking fix in this patch.

Maintainers, if this series is applied, could you please add the following?
Suggested-by: James Houghton <jthoughton@xxxxxxxxxx>

(I will be sure to include it if a v3 is otherwise required).