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@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
mm/huge_memory.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
--- 3.12-rc5/mm/huge_memory.c 2013-09-16 17:37:56.811072270 -0700
+++ linux/mm/huge_memory.c 2013-10-15 03:40:02.044138488 -0700
@@ -2697,6 +2697,7 @@ 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))) {
@@ -2719,7 +2720,14 @@ 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,
--
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