[PATCH v1] mm/balloon_compaction: avoid duplicate page removal

[Wei Wang <wei.w.wang@intel.com>]

Fixes: 418a3ab1e778 (mm/balloon_compaction: List interfaces)

A #GP is reported in the guest when requesting balloon inflation via
virtio-balloon. The reason is that the virtio-balloon driver has
removed the page from its internal page list (via balloon_page_pop),
but balloon_page_enqueue_one also calls "list_del"  to do the removal.
So remove the list_del in balloon_page_enqueue_one, and have the callers
do the page removal from their own page lists.

Signed-off-by: Wei Wang <wei.w.wang@intel.com>
---
 mm/balloon_compaction.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
index 83a7b61..1a5ddc4 100644
--- a/mm/balloon_compaction.c
+++ b/mm/balloon_compaction.c
@@ -11,6 +11,7 @@
 #include <linux/export.h>
 #include <linux/balloon_compaction.h>
 
+/* Callers ensure that @page has been removed from its original list. */
 static void balloon_page_enqueue_one(struct balloon_dev_info *b_dev_info,
 				     struct page *page)
 {
@@ -21,7 +22,6 @@ static void balloon_page_enqueue_one(struct balloon_dev_info *b_dev_info,
 	 * memory corruption is possible and we should stop execution.
 	 */
 	BUG_ON(!trylock_page(page));
-	list_del(&page->lru);
 	balloon_page_insert(b_dev_info, page);
 	unlock_page(page);
 	__count_vm_event(BALLOON_INFLATE);
@@ -47,6 +47,7 @@ size_t balloon_page_list_enqueue(struct balloon_dev_info *b_dev_info,
 
 	spin_lock_irqsave(&b_dev_info->pages_lock, flags);
 	list_for_each_entry_safe(page, tmp, pages, lru) {
+		list_del(&page->lru);
 		balloon_page_enqueue_one(b_dev_info, page);
 		n_pages++;
 	}
-- 
2.7.4