[dpdk-dev] [PATCH 1/3] vhost: fix deadlock due to vhostuser socket and fdset

[xiangxia.m.yue at gmail.com]

From: Tonghao Zhang <xiangxia.m.yue at gmail.com>

When qemu close the unix socket fd of the vhostuser as a
server, and then immediately delete the vhostuser port on
openvswitch. There will be a deadlock.

A thread (fdset event thread):       B thread:
1. fdset_event_dispatch              rte_vhost_driver_unregister
2. set the fd busy to 1.             lock vsocket->conn_mutex
3. vhost_user_read_cb                fdset_del waits busy changed to 0.
4. vhost peer closed, remove the
   conn from vsocket->conn_list:
   lock vsocket->conn_mutex

5. set the fd busy to 0

Fixes: 65388b43 ("vhost: fix fd leaks for vhost-user server mode")
Cc: stable at dpdk.org
Cc: Yuanhan Liu <yliu at fridaylinux.org>
Signed-off-by: Tonghao Zhang <xiangxia.m.yue at gmail.com>
---
 lib/librte_vhost/fd_man.c | 32 ++++++++++++++++++++++++++++++++
 lib/librte_vhost/fd_man.h |  1 +
 lib/librte_vhost/socket.c | 13 ++++++++++++-
 3 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/lib/librte_vhost/fd_man.c b/lib/librte_vhost/fd_man.c
index 8590ee5..b24c27d 100644
--- a/lib/librte_vhost/fd_man.c
+++ b/lib/librte_vhost/fd_man.c
@@ -174,6 +174,38 @@
 	return dat;
 }
 
+/**
+ *  Unregister the fd from the fdset.
+ *
+ *  If parameters are invalid, return directly -2.
+ *  And check whether fd is busy, if yes, return -1.
+ *  Otherwise, try to delete the fd from fdset and
+ *  return true.
+ */
+int
+fdset_try_del(struct fdset *pfdset, int fd)
+{
+	int i;
+
+	if (pfdset == NULL || fd == -1)
+		return -2;
+
+	pthread_mutex_lock(&pfdset->fd_mutex);
+	i = fdset_find_fd(pfdset, fd);
+	if (i != -1 && pfdset->fd[i].busy) {
+		pthread_mutex_unlock(&pfdset->fd_mutex);
+		return -1;
+	}
+
+	if (i != -1) {
+		pfdset->fd[i].fd = -1;
+		pfdset->fd[i].rcb = pfdset->fd[i].wcb = NULL;
+		pfdset->fd[i].dat = NULL;
+	}
+
+	pthread_mutex_unlock(&pfdset->fd_mutex);
+	return 0;
+}
 
 /**
  * This functions runs in infinite blocking loop until there is no fd in
diff --git a/lib/librte_vhost/fd_man.h b/lib/librte_vhost/fd_man.h
index 76a42fb..3331bcd 100644
--- a/lib/librte_vhost/fd_man.h
+++ b/lib/librte_vhost/fd_man.h
@@ -44,6 +44,7 @@ int fdset_add(struct fdset *pfdset, int fd,
 	fd_cb rcb, fd_cb wcb, void *dat);
 
 void *fdset_del(struct fdset *pfdset, int fd);
+int fdset_try_del(struct fdset *pfdset, int fd);
 
 void *fdset_event_dispatch(void *arg);
 
diff --git a/lib/librte_vhost/socket.c b/lib/librte_vhost/socket.c
index 4a561ad..822db41 100644
--- a/lib/librte_vhost/socket.c
+++ b/lib/librte_vhost/socket.c
@@ -922,13 +922,24 @@ struct vhost_user_reconnect_list {
 				vhost_user_remove_reconnect(vsocket);
 			}
 
+again:
 			pthread_mutex_lock(&vsocket->conn_mutex);
 			for (conn = TAILQ_FIRST(&vsocket->conn_list);
 			     conn != NULL;
 			     conn = next) {
 				next = TAILQ_NEXT(conn, next);
 
-				fdset_del(&vhost_user.fdset, conn->connfd);
+				/*
+				 * If r/wcb is executing, release the
+				 * conn_mutex lock, and try again since
+				 * the r/wcb may use the conn_mutex lock.
+				 */
+				if (fdset_try_del(&vhost_user.fdset,
+						  conn->connfd) == -1) {
+					pthread_mutex_unlock(&vsocket->conn_mutex);
+					goto again;
+				}
+
 				RTE_LOG(INFO, VHOST_CONFIG,
 					"free connfd = %d for device '%s'\n",
 					conn->connfd, path);
-- 
1.8.3.1