SUNRPC: Fix potential races in xprt_lock_write_next()

We have to ensure that the wake up from the waitqueue and the assignment
of xprt->snd_task are atomic. We can do this by assigning the snd_task
while under the waitqueue spinlock.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 26 insertions, 23 deletions

diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
index c64c0ef519b5..839f6ef2326b 100644
--- a/net/sunrpc/xprt.c
+++ b/net/sunrpc/xprt.c
@@ -292,54 +292,57 @@ static inline int xprt_lock_write(struct rpc_xprt *xprt, struct rpc_task *task)
 	return retval;
 }
 
-static void __xprt_lock_write_next(struct rpc_xprt *xprt)
+static bool __xprt_lock_write_func(struct rpc_task *task, void *data)
 {
-	struct rpc_task *task;
+	struct rpc_xprt *xprt = data;
 	struct rpc_rqst *req;
 
-	if (test_and_set_bit(XPRT_LOCKED, &xprt->state))
-		return;
-
-	task = rpc_wake_up_next(&xprt->sending);
-	if (task == NULL)
-		goto out_unlock;
-
 	req = task->tk_rqstp;
 	xprt->snd_task = task;
 	if (req) {
 		req->rq_bytes_sent = 0;
 		req->rq_ntrans++;
 	}
-	return;
+	return true;
+}
 
-out_unlock:
+static void __xprt_lock_write_next(struct rpc_xprt *xprt)
+{
+	if (test_and_set_bit(XPRT_LOCKED, &xprt->state))
+		return;
+
+	if (rpc_wake_up_first(&xprt->sending, __xprt_lock_write_func, xprt))
+		return;
 	xprt_clear_locked(xprt);
 }
 
-static void __xprt_lock_write_next_cong(struct rpc_xprt *xprt)
+static bool __xprt_lock_write_cong_func(struct rpc_task *task, void *data)
 {
-	struct rpc_task *task;
+	struct rpc_xprt *xprt = data;
 	struct rpc_rqst *req;
 
-	if (test_and_set_bit(XPRT_LOCKED, &xprt->state))
-		return;
-	if (RPCXPRT_CONGESTED(xprt))
-		goto out_unlock;
-	task = rpc_wake_up_next(&xprt->sending);
-	if (task == NULL)
-		goto out_unlock;
-
 	req = task->tk_rqstp;
 	if (req == NULL) {
 		xprt->snd_task = task;
-		return;
+		return true;
 	}
 	if (__xprt_get_cong(xprt, task)) {
 		xprt->snd_task = task;
 		req->rq_bytes_sent = 0;
 		req->rq_ntrans++;
-		return;
+		return true;
 	}
+	return false;
+}
+
+static void __xprt_lock_write_next_cong(struct rpc_xprt *xprt)
+{
+	if (test_and_set_bit(XPRT_LOCKED, &xprt->state))
+		return;
+	if (RPCXPRT_CONGESTED(xprt))
+		goto out_unlock;
+	if (rpc_wake_up_first(&xprt->sending, __xprt_lock_write_cong_func, xprt))
+		return;
 out_unlock:
 	xprt_clear_locked(xprt);
 }