From c8efc390c1e0eca195ae59a2f7cec46773620e0c Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" Date: Wed, 10 Aug 2016 16:27:52 -0700 Subject: [PATCH] mm, rmap: fix false positive VM_BUG() in page_add_file_rmap() PageTransCompound() doesn't distinguish THP from from any other type of compound pages. This can lead to false-positive VM_BUG_ON() in page_add_file_rmap() if called on compound page from a driver[1]. I think we can exclude such cases by checking if the page belong to a mapping. The VM_BUG_ON_PAGE() is downgraded to VM_WARN_ON_ONCE(). This path should not cause any harm to non-THP page, but good to know if we step on anything else. [1] http://lkml.kernel.org/r/c711e067-0bff-a6cb-3c37-04dfe77d2db1@redhat.com Link: http://lkml.kernel.org/r/20160810161345.GA67522@black.fi.intel.com Signed-off-by: Kirill A. Shutemov Reported-by: Laura Abbott Tested-by: Laura Abbott Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/rmap.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/mm/rmap.c b/mm/rmap.c index 709bc83703b1..d4f56060ba3f 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1284,8 +1284,9 @@ void page_add_file_rmap(struct page *page, bool compound) VM_BUG_ON_PAGE(!PageSwapBacked(page), page); __inc_node_page_state(page, NR_SHMEM_PMDMAPPED); } else { - if (PageTransCompound(page)) { - VM_BUG_ON_PAGE(!PageLocked(page), page); + if (PageTransCompound(page) && page_mapping(page)) { + VM_WARN_ON_ONCE(!PageLocked(page)); + SetPageDoubleMap(compound_head(page)); if (PageMlocked(page)) clear_page_mlock(compound_head(page)); -- 2.20.1