Commit 750e8165 authored Oct 16, 2013 by Hugh Dickins Committed by Linus Torvalds Oct 16, 2013

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 <hughd@google.com>
Acked-by: Kirill 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus 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,

Admin message