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>

diff --git a/mm/memory.c b/mm/memory.c
index 12ee1ea237f515b086eb01a30e69069eeb955ea9..31250faff39050bd6e45d9ace17cf5e9983ea8f2 100644 (file)
--- 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;
                        }