[PATCH] thp: avoid VM_BUG_ON page_count(page) false positives in __collapse_huge_page_copy

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Speculative cache pagecache lookups can elevate the refcount from
under us, so avoid the false positive. If the refcount is < 2 we'll be
notified by a VM_BUG_ON in put_page_testzero as there are two
put_page(src_page) in a row before returning from this function.

Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
---
 mm/huge_memory.c |    1 -
 1 files changed, 0 insertions(+), 1 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 1598708..ad56497 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1814,7 +1814,6 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
 			src_page = pte_page(pteval);
 			copy_user_highpage(page, src_page, address, vma);
 			VM_BUG_ON(page_mapcount(src_page) != 1);
-			VM_BUG_ON(page_count(src_page) != 2);
 			release_pte_page(src_page);
 			/*
 			 * ptl mostly unnecessary, but preempt has to

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