linux-kernel - Re: [PATCH] hugetlb: avoid gratuitous BUG_ON in hugetlb_fault() -> hugetlb

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Message-ID: <201205011333.q41DXsK7026759@farm-0013.internal.tilera.com>
Date:	Sun, 29 Apr 2012 15:04:51 -0400
From:	Chris Metcalf <cmetcalf@...era.com>
To:	Hugh Dickins <hughd@...gle.com>
CC:	Mel Gorman <mel@....ul.ie>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hillf Danton <dhillf@...il.com>, Michal Hocko <mhocko@...e.cz>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] hugetlb: avoid gratuitous BUG_ON in hugetlb_fault() ->
 hugetlb_cow()

Commit 66aebce747eaf added code to avoid a race condition by
elevating the page refcount in hugetlb_fault() while calling
hugetlb_cow().  However, one code path in hugetlb_cow() includes
an assertion that the page count is 1, whereas it may now also
have the value 2 in this path.  Consensus is that this BUG_ON
has served its purpose, so rather than extending it to cover both
cases, we just remove it.

Signed-off-by: Chris Metcalf <cmetcalf@...era.com>
---
 mm/hugetlb.c |    1 -
 1 files changed, 0 insertions(+), 1 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index cd65cb1..baaad5d 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2498,7 +2498,6 @@ retry_avoidcopy:
 		if (outside_reserve) {
 			BUG_ON(huge_pte_none(pte));
 			if (unmap_ref_private(mm, vma, old_page, address)) {
-				BUG_ON(page_count(old_page) != 1);
 				BUG_ON(huge_pte_none(pte));
 				spin_lock(&mm->page_table_lock);
 				ptep = huge_pte_offset(mm, address & huge_page_mask(h));
-- 
1.6.5.2

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