linux-kernel - [PATCH -v2] mm,numa: remove BUG_ON in __handle_mm

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Message-ID: <20140429153615.2d72098e@annuminas.surriel.com>
Date:	Tue, 29 Apr 2014 15:36:15 -0400
From:	Rik van Riel <riel@...hat.com>
To:	n-horiguchi@...jp.nec.com
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	lwoodman@...hat.com, peterz@...radead.org, mgorman@...e.de,
	dave.hansen@...el.com, sunil.k.pandey@...el.com
Subject: [PATCH -v2] mm,numa: remove BUG_ON in __handle_mm_fault

Peter pointed out we can do this slightly simpler, since we already
have a test for pmd_trans_huge(*pmd) below...

---8<---

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 turned into a numa one while __handle_mm_fault is examining
the value of old_pmd.

If that happens, __handle_mm_fault should just return and let
the page fault retry, instead of throwing an oops. This is
handled by the test for pmd_trans_huge(*pmd) below.

Signed-off-by: Rik van Riel <riel@...hat.com>
Reviewed-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Reported-by: Sunil Pandey <sunil.k.pandey@...el.com>
Cc: stable@...nel.org
---
 mm/memory.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index d0f0bef..9c2dc65 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3900,9 +3900,6 @@ 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));
-
 	/*
 	 * Use __pte_alloc instead of pte_alloc_map, because we can't
 	 * run pte_offset_map on the pmd, if an huge pmd could
--
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