memory: use RCU_READ_LOCK_GUARD

Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/exec/memory.h

diff --git a/include/exec/memory.h b/include/exec/memory.h
index 27a84e0..9d3fdb5 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -2171,7 +2171,7 @@
 
     if (__builtin_constant_p(len)) {
         if (len) {
-            rcu_read_lock();
+            RCU_READ_LOCK_GUARD();
             fv = address_space_to_flatview(as);
             l = len;
             mr = flatview_translate(fv, addr, &addr1, &l, false, attrs);
@@ -2182,7 +2182,6 @@
                 result = flatview_read_continue(fv, addr, attrs, buf, len,
                                                 addr1, l, mr);
             }
-            rcu_read_unlock();
         }
     } else {
         result = address_space_read_full(as, addr, attrs, buf, len);