linux-kernel - [PATCH -mm] mm,numa,mprotect: always continue after finding a stable thp page

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Message-ID: <20140306173137.6a23a0b2@cuia.bos.redhat.com>
Date:	Thu, 6 Mar 2014 17:31:37 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>, mgorman@...e.de,
	hhuang@...hat.com, knoel@...hat.com, aarcange@...hat.com
Subject: [PATCH -mm] mm,numa,mprotect: always continue after finding a
 stable thp page

On Thu, 06 Mar 2014 16:12:28 -0500
Sasha Levin <sasha.levin@...cle.com> wrote:

> While fuzzing with trinity inside a KVM tools guest running latest -next kernel I've hit the
> following spew. This seems to be introduced by your patch "mm,numa: reorganize change_pmd_range()".

That patch should not introduce any functional changes, except for
the VM_BUG_ON that catches the fact that we fell through to the 4kB
pte handling code, despite having just handled a THP pmd...

Does this patch fix the issue?

Mel, am I overlooking anything obvious? :)

---8<---

Subject: mm,numa,mprotect: always continue after finding a stable thp page

When turning a thp pmds into a NUMA one, change_huge_pmd will
return 0 when the pmd already is a NUMA pmd.

However, change_pmd_range would fall through to the code that
handles 4kB pages, instead of continuing on to the next pmd.

Signed-off-by: Rik van Riel <riel@...hat.com>
Reported-by: Sasha Levin <sasha.levin@...cle.com>
Cc: Mel Gorman <mgorman@...e.de>
---
 mm/mprotect.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/mprotect.c b/mm/mprotect.c
index 61f0a07..4746608 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -138,8 +138,8 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
 						pages += HPAGE_PMD_NR;
 						nr_huge_updates++;
 					}
-					continue;
 				}
+				continue;
 			}
 			/* fall through, the trans huge pmd just split */
 		}
--
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