thp: add debug checks for mapcount related invariants

Add debug checks for invariants that if broken could lead to mapcount vs
page_mapcount debug checks to trigger later in split_huge_page.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 2 deletions

diff --git a/mm/memory.c b/mm/memory.c
index 12ee1ea237f5..31250faff390 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -804,6 +804,7 @@ static inline int copy_pmd_range(struct mm_struct *dst_mm, struct mm_struct *src
                 next = pmd_addr_end(addr, end);
                 if (pmd_trans_huge(*src_pmd)) {
                         int err;
+                        VM_BUG_ON(next-addr != HPAGE_PMD_SIZE);
                         err = copy_huge_pmd(dst_mm, src_mm,
                                             dst_pmd, src_pmd, addr, vma);
                         if (err == -ENOMEM)
@@ -1015,9 +1016,10 @@ static inline unsigned long zap_pmd_range(struct mmu_gather *tlb,
         do {
                 next = pmd_addr_end(addr, end);
                 if (pmd_trans_huge(*pmd)) {
-                        if (next-addr != HPAGE_PMD_SIZE)
+                        if (next-addr != HPAGE_PMD_SIZE) {
+                                VM_BUG_ON(!rwsem_is_locked(&tlb->mm->mmap_sem));
                                 split_huge_page_pmd(vma->vm_mm, pmd);
-                        else if (zap_huge_pmd(tlb, vma, pmd)) {
+                        } else if (zap_huge_pmd(tlb, vma, pmd)) {
                                 (*zap_work)--;
                                 continue;
                         }