+ virtio_balloon-avoid-shrinker-execution-during-pm-suspend.patch added to mm-new branch

The patch titled
     Subject: virtio_balloon: avoid shrinker execution during PM suspend
has been added to the -mm mm-new branch.  Its filename is
     virtio_balloon-avoid-shrinker-execution-during-pm-suspend.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/virtio_balloon-avoid-shrinker-execution-during-pm-suspend.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: Link Lin <[email protected]>
Subject: virtio_balloon: avoid shrinker execution during PM suspend
Date: Fri, 17 Jul 2026 00:22:21 +0000

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.

Link: https://lore.kernel.org/[email protected]
Fixes: 71019de8219b ("virtio_balloon: Add free page hinting support")
Signed-off-by: Link Lin <[email protected]>
Acked-by: David Rientjes <[email protected]>
Suggested-by: James Houghton <[email protected]>
Cc: Michael S. Tsirkin <[email protected]>
Cc: Alexander Duyck <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Greg Thelen <[email protected]>
Cc: Jason Wang <[email protected]>
Cc: Jiaqi Yan <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Xuan Zhuo <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
---

 drivers/virtio/virtio_balloon.c |   49 +++++++++++++++++++++++++-----
 1 file changed, 41 insertions(+), 8 deletions(-)

--- a/drivers/virtio/virtio_balloon.c~virtio_balloon-avoid-shrinker-execution-during-pm-suspend
+++ a/drivers/virtio/virtio_balloon.c
@@ -68,6 +68,8 @@ struct virtio_balloon {
 	/* Prevent updating balloon when it is being canceled. */
 	spinlock_t stop_update_lock;
 	bool stop_update;
+	/* Prevent shrinker from running while device is suspended. */
+	bool suspended;
 	/* Bitmap to indicate if reading the related config fields are needed */
 	unsigned long config_read_bitmap;
 
@@ -471,9 +473,9 @@ static inline s64 towards_target(struct
 	return target - vb->num_pages;
 }
 
-/* Gives back @num_to_return blocks of free pages to mm. */
-static unsigned long return_free_pages_to_mm(struct virtio_balloon *vb,
-					     unsigned long num_to_return)
+/* Helper: must be called with free_page_list_lock held */
+static unsigned long __return_free_pages_to_mm(struct virtio_balloon *vb,
+					       unsigned long num_to_return)
 {
 	unsigned long num_returned = 0;
 	struct page *page, *next;
@@ -481,8 +483,6 @@ static unsigned long return_free_pages_t
 	if (unlikely(!num_to_return))
 		return 0;
 
-	spin_lock_irq(&vb->free_page_list_lock);
-
 	list_for_each_entry_safe(page, next, &vb->free_page_list, lru) {
 		list_del(&page->lru);
 		__free_pages(page, VIRTIO_BALLOON_HINT_BLOCK_ORDER);
@@ -490,11 +490,27 @@ static unsigned long return_free_pages_t
 			break;
 	}
 	vb->num_free_page_blocks -= num_returned;
-	spin_unlock_irq(&vb->free_page_list_lock);
 
 	return num_returned;
 }
 
+/* Gives back @num_to_return blocks of free pages to mm. */
+static unsigned long return_free_pages_to_mm(struct virtio_balloon *vb,
+					     unsigned long num_to_return)
+{
+	unsigned long ret;
+
+	spin_lock_irq(&vb->free_page_list_lock);
+	if (vb->suspended) {
+		spin_unlock_irq(&vb->free_page_list_lock);
+		return 0;
+	}
+	ret = __return_free_pages_to_mm(vb, num_to_return);
+	spin_unlock_irq(&vb->free_page_list_lock);
+
+	return ret;
+}
+
 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_shri
 {
 	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_shri
 {
 	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;
 }
 
@@ -1086,8 +1108,11 @@ static void remove_common(struct virtio_
 	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);
+	}
 
 	/* Now we reset the device so we can clean up the queues. */
 	virtio_reset_device(vb->vdev);
@@ -1130,6 +1155,10 @@ static int virtballoon_freeze(struct vir
 	 * The workqueue is already frozen by the PM core before this
 	 * function is called.
 	 */
+	spin_lock_irq(&vb->free_page_list_lock);
+	WRITE_ONCE(vb->suspended, true);
+	spin_unlock_irq(&vb->free_page_list_lock);
+
 	remove_common(vb);
 	return 0;
 }
@@ -1145,6 +1174,10 @@ static int virtballoon_restore(struct vi
 
 	virtio_device_ready(vdev);
 
+	spin_lock_irq(&vb->free_page_list_lock);
+	WRITE_ONCE(vb->suspended, false);
+	spin_unlock_irq(&vb->free_page_list_lock);
+
 	if (towards_target(vb))
 		virtballoon_changed(vdev);
 	update_balloon_size(vb);
_

Patches currently in -mm which might be from [email protected] are

mm-page_reporting-use-system_freezable_wq-to-fix-uaf-during-suspend.patch
virtio_balloon-avoid-shrinker-execution-during-pm-suspend.patch