[PATCH] mm,numa: remove BUG_ON in __handle_mm_fault

[Rik van Riel <riel@redhat.com>]

Changing PTEs and PMDs to pte_numa & pmd_numa is done with the
mmap_sem held for reading, which means a pmd can be instantiated
and/or turned into a numa one while __handle_mm_fault is examining
the value of orig_pmd.

If that happens, __handle_mm_fault should just return and let
the page fault retry, instead of throwing an oops.

Signed-off-by: Rik van Riel <riel@redhat.com>
Reported-by: Sunil Pandey <sunil.k.pandey@intel.com>
---
 mm/memory.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index d0f0bef..9edccb2 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3900,8 +3900,9 @@ static int __handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 		}
 	}
 
-	/* THP should already have been handled */
-	BUG_ON(pmd_numa(*pmd));
+	/* The PMD became NUMA while we examined orig_pmd. Return & retry */
+	if (pmd_numa(*pmd))
+		return 0;
 
 	/*
 	 * Use __pte_alloc instead of pte_alloc_map, because we can't

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