[RFC, 2.6.26.2-rc1] Fix shared mmap when more than two maps of the same file exist

[Oliver Pinter <oliver@zipernowsky.hu>]

>From 53cdb27a933e4032934cbda0b447cfc9943c0eac Mon Sep 17 00:00:00 2001
From: Russell King <rmk@dyn-67.arm.linux.org.uk>
Date: Sun, 27 Jul 2008 10:35:54 +0100
Subject: [PATCH] [ARM] Fix shared mmap when more than two maps of the same
file exist

[ Upstream commit 53cdb27a933e4032934cbda0b447cfc9943c0eac ]

The shared mmap code works fine for the test case, which only checked
for two shared maps of the same file.  However, three shared maps
result in one mapping remaining cached, resulting in stale data being
visible via that mapping.  Fix this.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
CC: Oliver Pinter <oliver.pntr@gmail.com>

diff --git a/arch/arm/mm/fault-armv.c b/arch/arm/mm/fault-armv.c
index fbfa260..a8ec97b 100644
--- a/arch/arm/mm/fault-armv.c
+++ b/arch/arm/mm/fault-armv.c
@@ -37,7 +37,7 @@ static int adjust_pte(struct vm_area_struct *vma,
unsigned long address)
 	pgd_t *pgd;
 	pmd_t *pmd;
 	pte_t *pte, entry;
-	int ret = 0;
+	int ret;
 
 	pgd = pgd_offset(vma->vm_mm, address);
 	if (pgd_none(*pgd))
@@ -55,15 +55,19 @@ static int adjust_pte(struct vm_area_struct *vma,
unsigned long address)
 	entry = *pte;
 
 	/*
+	 * If this page is present, it's actually being shared.
+	 */
+	ret = pte_present(entry);
+
+	/*
 	 * If this page isn't present, or is already setup to
 	 * fault (ie, is old), we can safely ignore any issues.
 	 */
-	if (pte_present(entry) && pte_val(entry) & shared_pte_mask) {
+	if (ret && pte_val(entry) & shared_pte_mask) {
 		flush_cache_page(vma, address, pte_pfn(entry));
 		pte_val(entry) &= ~shared_pte_mask;
 		set_pte_at(vma->vm_mm, address, pte, entry);
 		flush_tlb_page(vma, address);
-		ret = 1;
 	}
 	pte_unmap(pte);
 	return ret;