Index: sys/dev/acpica/acpi.c
===================================================================
--- sys/dev/acpica/acpi.c	(revision 196060)
+++ sys/dev/acpica/acpi.c	(working copy)
@@ -2528,6 +2528,11 @@ acpi_EnterSleepState(struct acpi_softc *sc, int st
     thread_unlock(curthread);
 #endif
 
+    /*
+     * Acquire Giant because some thirdy part handlers for suspend/resume
+     * events may not be alredy converted to newbus lock.
+     */
+    mtx_lock(&Giant);
     newbus_xlock();
 
     slp_state = ACPI_SS_NONE;
@@ -2602,6 +2607,7 @@ backout:
 	acpi_enable_fixed_events(sc);
 
     newbus_xunlock();
+    mtx_unlock(&Giant);
 
 #ifdef SMP
     thread_lock(curthread);