linux-kernel - linux-next: missing merge fix for the access

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Message-ID: <20141223131749.78087632@canb.auug.org.au>
Date:	Tue, 23 Dec 2014 13:17:49 +1100
From:	Stephen Rothwell <sfr@...b.auug.org.au>
To:	Linus <torvalds@...ux-foundation.org>
Cc:	Christian Borntraeger <borntraeger@...ibm.com>,
	<linux-next@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: linux-next: missing merge fix for the access_once tree

Hi Linus,

I have been carrying this merge fix patch for some time.  It should
have gone into the merge of the access_once tree.

From: Christian Borntraeger <borntraeger@...ibm.com>
Date: Sun, 7 Dec 2014 22:01:59 +0100
Subject: [PATCH] x86/xen/p2m: Replace ACCESS_ONCE with READ_ONCE

ACCESS_ONCE does not work reliably on non-scalar types. For
example gcc 4.6 and 4.7 might remove the volatile tag for such
accesses during the SRA (scalar replacement of aggregates) step
(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145)

Change the p2m code to replace ACCESS_ONCE with READ_ONCE.

Signed-off-by: Christian Borntraeger <borntraeger@...ibm.com>
---
 arch/x86/xen/p2m.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
index 8b5db51..08ddf91 100644
--- a/arch/x86/xen/p2m.c
+++ b/arch/x86/xen/p2m.c
@@ -554,7 +554,7 @@ static bool alloc_p2m(unsigned long pfn)
 		mid_mfn = NULL;
 	}
 
-	p2m_pfn = pte_pfn(ACCESS_ONCE(*ptep));
+	p2m_pfn = pte_pfn(READ_ONCE(*ptep));
 	if (p2m_pfn == PFN_DOWN(__pa(p2m_identity)) ||
 	    p2m_pfn == PFN_DOWN(__pa(p2m_missing))) {
 		/* p2m leaf page is missing */
-- 
1.8.5.5

-- 
Cheers,
Stephen Rothwell                    sfr@...b.auug.org.au

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