[PATCH 2/4] UBUNTU: xen: Check for NULL pointer before using pgd

[Stefan Bader]

In pgd_alloc(), the test for the new pgd being NULL is done
after it has already been used for test_and_unpin(). Do that
check before.

BugLink: http://bugs.launchpad.net/bugs/705562

Signed-off-by: Stefan Bader <stefan.bader at canonical.com>
---
 arch/x86/mm/pgtable_32-xen.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/arch/x86/mm/pgtable_32-xen.c b/arch/x86/mm/pgtable_32-xen.c
index 74a2e57..48242aa 100644
--- a/arch/x86/mm/pgtable_32-xen.c
+++ b/arch/x86/mm/pgtable_32-xen.c
@@ -345,9 +345,12 @@ pgd_t *pgd_alloc(struct mm_struct *mm)
 	pmd_t **pmds = NULL;
 	unsigned long flags;
 
+	if (!pgd)
+		return NULL;
+
 	pgd_test_and_unpin(pgd);
 
-	if (PTRS_PER_PMD == 1 || !pgd)
+	if (PTRS_PER_PMD == 1)
 		return pgd;
 
 #ifdef CONFIG_XEN
-- 
1.7.4.1