vhost: fix deadlock on port deletion

If the vhost-user application (e.g. OVS) deletes the vhost-user
port while Qemu sends a vhost-user request, a deadlock can
happen if the request handler tries to acquire vhost-user's
global mutex, which is also locked by the vhost-user port
deletion API (rte_vhost_driver_unregister).

This patch prevents the deadlock by making
rte_vhost_driver_unregister() to release the mutex and try
again if a request is being handled to give a chance to
the request handler to complete.

Fixes: 8b4b949144b8 ("vhost: fix dead lock on closing in server mode")
Fixes: 5fbb3941da9f ("vhost: introduce driver features related APIs")
Cc: stable@dpdk.org
Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Reviewed-by: Tiwei Bie <tiwei.bie@intel.com>
Acked-by: Eelco Chaudron <echaudro@redhat.com>

diff --git a/lib/librte_vhost/socket.c b/lib/librte_vhost/socket.c
index 8bc1e3a..9740fb3 100644 (file)
--- a/lib/librte_vhost/socket.c
+++ b/lib/librte_vhost/socket.c
@@ -1052,9 +1052,10 @@ again:
                                next = TAILQ_NEXT(conn, next);
 
                                /*
-                                * If r/wcb is executing, release the
-                                * conn_mutex lock, and try again since
-                                * the r/wcb may use the conn_mutex lock.
+                                * If r/wcb is executing, release vsocket's
+                                * conn_mutex and vhost_user's mutex locks, and
+                                * try again since the r/wcb may use the
+                                * conn_mutex and mutex locks.
                                 */
                                if (fdset_try_del(&vhost_user.fdset,
                                                  conn->connfd) == -1) {
@@ -1075,8 +1076,17 @@ again:
                        pthread_mutex_unlock(&vsocket->conn_mutex);
 
                        if (vsocket->is_server) {
-                               fdset_del(&vhost_user.fdset,
-                                               vsocket->socket_fd);
+                               /*
+                                * If r/wcb is executing, release vhost_user's
+                                * mutex lock, and try again since the r/wcb
+                                * may use the mutex lock.
+                                */
+                               if (fdset_try_del(&vhost_user.fdset,
+                                               vsocket->socket_fd) == -1) {
+                                       pthread_mutex_unlock(&vhost_user.mutex);
+                                       goto again;
+                               }
+
                                close(vsocket->socket_fd);
                                unlink(path);
                        } else if (vsocket->reconnect) {