SUNRPC: Ensure we release the socket write lock if the rpc_task exits early

If the rpc_task exits while holding the socket write lock before it has
allocated an rpc slot, then the usual mechanism for releasing the write
lock in xprt_release() is defeated.

The problem occurs if the call to xprt_lock_write() initially fails, so
that the rpc_task is put on the xprt->sending wait queue. If the task
exits after being assigned the lock by __xprt_lock_write_func, but
before it has retried the call to xprt_lock_and_alloc_slot(), then
it calls xprt_release() while holding the write lock, but will
immediately exit due to the test for task->tk_rqstp != NULL.

Reported-by: Chris Perl <chris.perl@gmail.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: stable@vger.kernel.org [>= 3.1]

2 files changed, 11 insertions, 4 deletions

diff --git a/net/sunrpc/sched.c b/net/sunrpc/sched.c
index b4133bd13915..bfa31714581f 100644
--- a/net/sunrpc/sched.c
+++ b/net/sunrpc/sched.c
@@ -972,8 +972,7 @@ static void rpc_async_release(struct work_struct *work)
 
 static void rpc_release_resources_task(struct rpc_task *task)
 {
-        if (task->tk_rqstp)
-                xprt_release(task);
+        xprt_release(task);
         if (task->tk_msg.rpc_cred) {
                 put_rpccred(task->tk_msg.rpc_cred);
                 task->tk_msg.rpc_cred = NULL;
diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
index bd462a532acf..33811db8788a 100644
--- a/net/sunrpc/xprt.c
+++ b/net/sunrpc/xprt.c
@@ -1136,10 +1136,18 @@ static void xprt_request_init(struct rpc_task *task, struct rpc_xprt *xprt)
 void xprt_release(struct rpc_task *task)
 {
         struct rpc_xprt *xprt;
-        struct rpc_rqst *req;
+        struct rpc_rqst *req = task->tk_rqstp;
 
-        if (!(req = task->tk_rqstp))
+        if (req == NULL) {
+                if (task->tk_client) {
+                        rcu_read_lock();
+                        xprt = rcu_dereference(task->tk_client->cl_xprt);
+                        if (xprt->snd_task == task)
+                                xprt_release_write(xprt, task);
+                        rcu_read_unlock();
+                }
                 return;
+        }
 
         xprt = req->rq_xprt;
         if (task->tk_ops->rpc_count_stats != NULL)