linux-kernel - [PATCH 13/16] ksm: Replace smp_read_barrier_depends() with lockless

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Date:	Thu, 13 Nov 2014 14:24:19 -0500
From:	Pranith Kumar <bobby.prani@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	David Rientjes <rientjes@...gle.com>,
	Joerg Roedel <jroedel@...e.de>, NeilBrown <neilb@...e.de>,
	Sasha Levin <sasha.levin@...cle.com>,
	Paul McQuade <paulmcquad@...il.com>,
	linux-mm@...ck.org (open list:MEMORY MANAGEMENT),
	linux-kernel@...r.kernel.org (open list)
Cc:	paulmck@...ux.vnet.ibm.com
Subject: [PATCH 13/16] ksm: Replace smp_read_barrier_depends() with lockless_dereference()

Recently lockless_dereference() was added which can be used in place of
hard-coding smp_read_barrier_depends(). The following PATCH makes the change.

Signed-off-by: Pranith Kumar <bobby.prani@...il.com>
---
 mm/ksm.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/mm/ksm.c b/mm/ksm.c
index d247efa..a67de79 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -542,15 +542,14 @@ static struct page *get_ksm_page(struct stable_node *stable_node, bool lock_it)
 	expected_mapping = (void *)stable_node +
 				(PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
 again:
-	kpfn = ACCESS_ONCE(stable_node->kpfn);
-	page = pfn_to_page(kpfn);
-
 	/*
 	 * page is computed from kpfn, so on most architectures reading
 	 * page->mapping is naturally ordered after reading node->kpfn,
 	 * but on Alpha we need to be more careful.
 	 */
-	smp_read_barrier_depends();
+	kpfn = lockless_dereference(stable_node->kpfn);
+	page = pfn_to_page(kpfn);
+
 	if (ACCESS_ONCE(page->mapping) != expected_mapping)
 		goto stale;
 
-- 
1.9.1

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