diff --git a/arch/arm/xen/p2m.c b/arch/arm/xen/p2m.c
index acb464547a54..4a1991a103ea 100644
--- a/arch/arm/xen/p2m.c
+++ b/arch/arm/xen/p2m.c
@@ -62,11 +62,12 @@ static int xen_add_phys_to_mach_entry(struct xen_p2m_entry *new)
 
 unsigned long __pfn_to_mfn(unsigned long pfn)
 {
-	struct rb_node *n = phys_to_mach.rb_node;
+	struct rb_node *n;
 	struct xen_p2m_entry *entry;
 	unsigned long irqflags;
 
 	read_lock_irqsave(&p2m_lock, irqflags);
+	n = phys_to_mach.rb_node;
 	while (n) {
 		entry = rb_entry(n, struct xen_p2m_entry, rbnode_phys);
 		if (entry->pfn <= pfn &&
@@ -153,10 +154,11 @@ bool __set_phys_to_machine_multi(unsigned long pfn,
 	int rc;
 	unsigned long irqflags;
 	struct xen_p2m_entry *p2m_entry;
-	struct rb_node *n = phys_to_mach.rb_node;
+	struct rb_node *n;
 
 	if (mfn == INVALID_P2M_ENTRY) {
 		write_lock_irqsave(&p2m_lock, irqflags);
+		n = phys_to_mach.rb_node;
 		while (n) {
 			p2m_entry = rb_entry(n, struct xen_p2m_entry, rbnode_phys);
 			if (p2m_entry->pfn <= pfn &&