diff --git a/acinclude.m4 b/acinclude.m4
index adc2b5ef12..36df23026c 100644
--- a/acinclude.m4
+++ b/acinclude.m4
@@ -697,6 +697,7 @@ case $AFS_SYSNAME in *_linux* | *_umlinux*)
                  LINUX_EXPORTS_SYS_CLOSE
                  LINUX_EXPORTS_SYS_OPEN
                  LINUX_EXPORTS_SYS_WAIT4
+		 LINUX_EXPORTS_RCU_READ_LOCK
 		 LINUX_WHICH_MODULES
                  if test "x$ac_cv_linux_config_modversions" = "xno" -o $AFS_SYSKVERS -ge 26; then
                    AC_MSG_WARN([Cannot determine sys_call_table status. assuming it isn't exported])
diff --git a/src/afs/LINUX/osi_groups.c b/src/afs/LINUX/osi_groups.c
index 9f1e618dcf..752057de56 100644
--- a/src/afs/LINUX/osi_groups.c
+++ b/src/afs/LINUX/osi_groups.c
@@ -51,12 +51,14 @@ afs_setgroups(cred_t **cr, struct group_info *group_info, int change_parent)
 
     crset(*cr);
 
+#ifdef STRUCT_TASK_STRUCT_HAS_PARENT
     if (change_parent) {
 	old_info = current->parent->group_info;
 	get_group_info(group_info);
 	current->parent->group_info = group_info;
 	put_group_info(old_info);
     }
+#endif
 
     return (0);
 }
@@ -625,32 +627,40 @@ extern rwlock_t tasklist_lock __attribute__((weak));
 void osi_keyring_init(void)
 {
     struct task_struct *p;
+
+    /* If we can't lock the tasklist, either with its explicit lock,
+     * or by using the RCU lock, then we can't safely work out the 
+     * type of a keyring. So, we have to rely on the weak reference. 
+     * If that's not available, then keyring based PAGs won't work.
+     */
     
+#if defined(EXPORTED_TASKLIST_LOCK) || (LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,16) && defined(EXPORTED_RCU_READ_LOCK))
     if (__key_type_keyring == NULL) {
-#ifdef EXPORTED_TASKLIST_LOCK
+# ifdef EXPORTED_TASKLIST_LOCK
 	if (&tasklist_lock)
 	    read_lock(&tasklist_lock);
-#endif
-#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,16)
-# ifdef EXPORTED_TASKLIST_LOCK
- 	else
 # endif
+# if (LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,16) && defined(EXPORTED_RCU_READ_LOCK))
+#  ifdef EXPORTED_TASKLIST_LOCK
+ 	else
+#  endif
 	    rcu_read_lock();
-#endif
+# endif
 	p = find_task_by_pid(1);
 	if (p && p->user->session_keyring)
 	    __key_type_keyring = p->user->session_keyring->type;
-#ifdef EXPORTED_TASKLIST_LOCK
+# ifdef EXPORTED_TASKLIST_LOCK
 	if (&tasklist_lock)
 	    read_unlock(&tasklist_lock);
-#endif
-#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,16)
-# ifdef EXPORTED_TASKLIST_LOCK
-	else
 # endif
+# if (LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,16) && defined(EXPORTED_RCU_READ_LOCK))
+#  ifdef EXPORTED_TASKLIST_LOCK
+	else
+#  endif
 	    rcu_read_unlock();
-#endif
+# endif
     }
+#endif
 
     register_key_type(&key_type_afs_pag);
 }
diff --git a/src/cf/linux-test4.m4 b/src/cf/linux-test4.m4
index 09e713dde1..448d55143b 100644
--- a/src/cf/linux-test4.m4
+++ b/src/cf/linux-test4.m4
@@ -999,3 +999,16 @@ printk("%x\n", _nd.path);],
       ac_cv_linux_struct_nameidata_has_path=no)])
   AC_MSG_RESULT($ac_cv_linux_struct_nameidata_has_path)])
 
+AC_DEFUN([LINUX_EXPORTS_RCU_READ_LOCK], [
+  AC_MSG_CHECKING([if rcu_read_lock is usable])
+  AC_CACHE_VAL([ac_cv_linux_exports_rcu_read_lock], [
+    AC_TRY_KBUILD(
+[#include <linux/rcupdate.h>],
+[rcu_read_lock();],
+      ac_cv_linux_exports_rcu_read_lock=yes,
+      ac_cv_linux_exports_rcu_read_lock=no)])
+  AC_MSG_RESULT($ac_cv_linux_exports_rcu_read_lock)
+  if test "x$ac_cv_linux_exports_rcu_read_lock" = "xyes"; then
+    AC_DEFINE([EXPORTED_RCU_READ_LOCK], 1, [define if rcu_read_lock() is usable])
+  fi])
+