thp: avoid VM_BUG_ON page_count(page) false positives in __collapse_h…

…uge_page_copy 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 <[email protected]> Reviewed-by: Rik van Riel <[email protected]> Reviewed-by: Johannes Weiner <[email protected]> Cc: Hugh Dickins <[email protected]> Cc: Mel Gorman <[email protected]> Cc: Petr Holasek <[email protected]> Cc: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
TechNexion · Sep 28, 2012 · 99a1300 · 99a1300
1 parent 6399413
commit 99a1300
Showing 1 changed file with 0 additions and 1 deletion.
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
@@ -1811,7 +1811,6 @@ 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