linux-kernel - [PATCH 1/1] powerpc/mm: Add memory barrier in __hugepte

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Message-ID: <20160405190547.GA12673@us.ibm.com>
Date:	Tue, 5 Apr 2016 12:05:47 -0700
From:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
To:	Michael Ellerman <mpe@...erman.id.au>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linuxppc-dev@...ts.ozlabs.org, James Dykman <jdykman@...ibm.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Subject: [PATCH 1/1] powerpc/mm: Add memory barrier in __hugepte_alloc()

>From f7b73c6b4508fe9b141a43d92be2f9dd7d3c4a58 Mon Sep 17 00:00:00 2001
From: Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
Date: Thu, 24 Mar 2016 02:07:57 -0400
Subject: [PATCH 1/1] powerpc/mm: Add memory barrier in __hugepte_alloc()

__hugepte_alloc() uses kmem_cache_zalloc() to allocate a zeroed PTE
and proceeds to use the newly allocated PTE. Add a memory barrier to
make sure that the other CPUs see a properly initialized PTE.

Based on a fix suggested by James Dykman.

Reported-by: James Dykman <jdykman@...ibm.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
Signed-off-by: Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
Tested-by: James Dykman <jdykman@...ibm.com>
---
Note:
	The bug was encountered and fix tested on an older version
	of the kernel. Forward porting to mainline.
---
 arch/powerpc/mm/hugetlbpage.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
index d991b9e..081f679 100644
--- a/arch/powerpc/mm/hugetlbpage.c
+++ b/arch/powerpc/mm/hugetlbpage.c
@@ -81,6 +81,13 @@ static int __hugepte_alloc(struct mm_struct *mm, hugepd_t *hpdp,
 	if (! new)
 		return -ENOMEM;
 
+	/*
+	 * Make sure other cpus find the hugepd set only after a
+	 * properly initialized page table is visible to them.
+	 * For more details look for comment in __pte_alloc().
+	 */
+	smp_wmb();
+
 	spin_lock(&mm->page_table_lock);
 #ifdef CONFIG_PPC_FSL_BOOK3E
 	/*
-- 
1.8.3.1