Commit 2668db91 authored by Adam Litke's avatar Adam Litke Committed by Linus Torvalds
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hugetlb: correct page count for surplus huge pages

Free pages in the hugetlb pool are free and as such have a reference count of
zero.  Regular allocations into the pool from the buddy are "freed" into the
pool which results in their page_count dropping to zero.  However, surplus
pages can be directly utilized by the caller without first being freed to the
pool.  Therefore, a call to put_page_testzero() is in order so that such a
page will be handed to the caller with a correct count.

This has not affected end users because the bad page count is reset before the
page is handed off.  However, under CONFIG_DEBUG_VM this triggers a BUG when
the page count is validated.

Thanks go to Mel for first spotting this issue and providing an initial fix.
Signed-off-by: default avatarAdam Litke <>
Cc: Mel Gorman <>
Cc: Dave Hansen <>
Cc: William Lee Irwin III <>
Cc: Andy Whitcroft <>
Cc: Mel Gorman <>
Cc: David Gibson <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 84207805
......@@ -286,6 +286,12 @@ static struct page *alloc_buddy_huge_page(struct vm_area_struct *vma,
if (page) {
* This page is now managed by the hugetlb allocator and has
* no users -- drop the buddy allocator's reference.
nid = page_to_nid(page);
set_compound_page_dtor(page, free_huge_page);
......@@ -369,13 +375,14 @@ free:
else {
* Decrement the refcount and free the page using its
* destructor. This must be done with hugetlb_lock
* The page has a reference count of zero already, so
* call free_huge_page directly instead of using
* put_page. This must be done with hugetlb_lock
* unlocked which is safe because free_huge_page takes
* hugetlb_lock before deciding how to free the page.
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