From 750e8165f5e87b6a142be953640eabb13a9d350a Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Wed, 16 Oct 2013 13:47:08 -0700 Subject: [PATCH] mm: fix BUG in __split_huge_page_pmd 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 Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/huge_memory.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 7489884682d8..610e3df2768a 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2697,6 +2697,7 @@ void __split_huge_page_pmd(struct vm_area_struct *vma, unsigned long address, 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))) { @@ -2719,7 +2720,14 @@ void __split_huge_page_pmd(struct vm_area_struct *vma, unsigned long address, 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, -- 2.34.1