From 750e8165f5e87b6a142be953640eabb13a9d350a Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Wed, 16 Oct 2013 13:47:08 -0700 Subject: mm: fix BUG in __split_huge_page_pmd From: Hugh Dickins commit 750e8165f5e87b6a142be953640eabb13a9d350a upstream. Occasionally we hit the BUG_ON(pmd_trans_huge(*pmd)) at the end of __split_huge_page_pmd(): seen when doing madvise(,,MADV_DONTNEED). It's invalid: we don't always have down_write of mmap_sem there: a racing do_huge_pmd_wp_page() might have copied-on-write to another huge page before our split_huge_page() got the anon_vma lock. Forget the BUG_ON, just go back and try again if this happens. Signed-off-by: Hugh Dickins Acked-by: Kirill A. Shutemov Cc: Andrea Arcangeli Cc: Naoya Horiguchi Cc: David Rientjes Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- mm/huge_memory.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2709,6 +2709,7 @@ void __split_huge_page_pmd(struct vm_are mmun_start = haddr; mmun_end = haddr + HPAGE_PMD_SIZE; +again: mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end); spin_lock(&mm->page_table_lock); if (unlikely(!pmd_trans_huge(*pmd))) { @@ -2731,7 +2732,14 @@ void __split_huge_page_pmd(struct vm_are split_huge_page(page); put_page(page); - BUG_ON(pmd_trans_huge(*pmd)); + + /* + * We don't always have down_write of mmap_sem here: a racing + * do_huge_pmd_wp_page() might have copied-on-write to another + * huge page before our split_huge_page() got the anon_vma lock. + */ + if (unlikely(pmd_trans_huge(*pmd))) + goto again; } void split_huge_page_pmd_mm(struct mm_struct *mm, unsigned long address,