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Commit 750e8165 authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
Browse files

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: default avatarHugh Dickins <hughd@google.com>
Acked-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: David Rientjes <rientjes@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 5b808a23

mm/huge_memory.c

+9 −1
Original line number Diff line number Diff line
@@ -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,