diff --git a/cpus.c b/cpus.c
index c09fbef5de0ad26f710d376969e42b7d2844ee12..f547aebeaf3fe0680ca0613f5f23e96f8ab0ef01 100644
--- a/cpus.c
+++ b/cpus.c
@@ -1146,6 +1146,13 @@ bool qemu_in_vcpu_thread(void)
     return current_cpu && qemu_cpu_is_self(current_cpu);
 }
 
+static __thread bool iothread_locked = false;
+
+bool qemu_mutex_iothread_locked(void)
+{
+    return iothread_locked;
+}
+
 void qemu_mutex_lock_iothread(void)
 {
     atomic_inc(&iothread_requesting_mutex);
@@ -1164,10 +1171,12 @@ void qemu_mutex_lock_iothread(void)
         atomic_dec(&iothread_requesting_mutex);
         qemu_cond_broadcast(&qemu_io_proceeded_cond);
     }
+    iothread_locked = true;
 }
 
 void qemu_mutex_unlock_iothread(void)
 {
+    iothread_locked = false;
     qemu_mutex_unlock(&qemu_global_mutex);
 }
 
diff --git a/include/qemu/main-loop.h b/include/qemu/main-loop.h
index 0f4a0fd4b2c35bf0b63e03e5e3d2419084037d52..bc18ca30e4a8fec577b103aebd8006e27be1ec50 100644
--- a/include/qemu/main-loop.h
+++ b/include/qemu/main-loop.h
@@ -222,6 +222,16 @@ void qemu_set_fd_handler(int fd,
 int qemu_add_child_watch(pid_t pid);
 #endif
 
+/**
+ * qemu_mutex_iothread_locked: Return lock status of the main loop mutex.
+ *
+ * The main loop mutex is the coarsest lock in QEMU, and as such it
+ * must always be taken outside other locks.  This function helps
+ * functions take different paths depending on whether the current
+ * thread is running within the main loop mutex.
+ */
+bool qemu_mutex_iothread_locked(void);
+
 /**
  * qemu_mutex_lock_iothread: Lock the main loop mutex.
  *
diff --git a/stubs/iothread-lock.c b/stubs/iothread-lock.c
index 5d8aca1b37d63cba061b9bee43162b4fb905e9a3..dda6f6b58dcb72342b6fc824dd943ada1ce35f48 100644
--- a/stubs/iothread-lock.c
+++ b/stubs/iothread-lock.c
@@ -1,6 +1,11 @@
 #include "qemu-common.h"
 #include "qemu/main-loop.h"
 
+bool qemu_mutex_iothread_locked(void)
+{
+    return true;
+}
+
 void qemu_mutex_lock_iothread(void)
 {
 }