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Subject: Re: [PATCH v22 2/3] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_VQ

On 01/18/2018 12:44 AM, Michael S. Tsirkin wrote:
On Wed, Jan 17, 2018 at 01:10:11PM +0800, Wei Wang wrote:
+static void virtballoon_changed(struct virtio_device *vdev)
+	struct virtio_balloon *vb = vdev->priv;
+	unsigned long flags;
+	__u32 cmd_id;
+	s64 diff = towards_target(vb);
+	if (diff) {
+		spin_lock_irqsave(&vb->stop_update_lock, flags);
+		if (!vb->stop_update)
Why do you ignore stop_update for freeze?
This means new wq entries can be added during remove
causing use after free issues.

I think stop_update isn't needed, because the lock has already been handled internally by the APIs. Similar examples like mem_cgroup_css_free() in "mm/memcontrol.c", there is no such locks used for cancel_work_sync(&memcg->high_work).


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