From 842e7d362d0c6231ba71341b07b51dc5cdcc0914 Mon Sep 17 00:00:00 2001
From: Patrick J Cherry <patrick@bytemark.co.uk>
Date: Fri, 7 Dec 2018 16:32:58 +0000
Subject: [PATCH] Ensure control socket is closed first, and wait for it to
 close.

---
 src/server/control.c |  8 ++++++++
 src/server/control.h |  1 +
 src/server/serve.c   | 19 +++++++++++++------
 3 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/src/server/control.c b/src/server/control.c
index 394854e..51e58e9 100644
--- a/src/server/control.c
+++ b/src/server/control.c
@@ -78,6 +78,14 @@ void control_destroy(struct control *control)
     free(control);
 }
 
+void control_wait_for_close(struct control *control)
+{
+    NULLCHECK(control);
+    while (!fd_is_closed(control->control_fd)) {
+       usleep(10000);
+    }
+}
+
 struct control_client *control_client_create(struct flexnbd *flexnbd,
 					     int client_fd,
 					     struct mbox *state_mbox)
diff --git a/src/server/control.h b/src/server/control.h
index 017611d..551265f 100644
--- a/src/server/control.h
+++ b/src/server/control.h
@@ -47,6 +47,7 @@ struct control_client {
 struct control *control_create(struct flexnbd *,
 			       const char *control_socket_name);
 void control_signal_close(struct control *);
+void control_wait_for_close(struct control *control);
 void control_destroy(struct control *);
 
 void *control_runner(void *);
diff --git a/src/server/serve.c b/src/server/serve.c
index 28970aa..c262189 100644
--- a/src/server/serve.c
+++ b/src/server/serve.c
@@ -820,14 +820,21 @@ void serve_cleanup(struct server *params,
     void *status;
 
     info("cleaning up");
-
-    if (params->server_fd) {
-	close(params->server_fd);
-    }
-
-    /* close the control socket too */
+    
+    /* Close the control socket, and wait for it to close before proceeding.
+     * If we do not wait, we risk a race condition with the tail supervisor
+     * sending a status command, and deadlocking the mirroring.  */
     if (params->flexnbd && params->flexnbd->control) {
+	debug("closing control socket");
         control_signal_close(params->flexnbd->control);
+
+	debug("waiting for control socket to close");
+	control_wait_for_close(params->flexnbd->control);
+    }
+    
+    if (params->server_fd) {
+	debug("closing server_fd");
+	close(params->server_fd);
     }
 
     /* need to stop background build if we're killed very early on */