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>

fs/nfs/nfs4state.c

diff --git a/fs/nfs/nfs4state.c b/fs/nfs/nfs4state.c
index a42e60d..f0e9881 100644
--- a/fs/nfs/nfs4state.c
+++ b/fs/nfs/nfs4state.c
@@ -190,23 +190,22 @@
 static void nfs4_end_drain_session(struct nfs_client *clp)
 {
 	struct nfs4_session *ses = clp->cl_session;
+	struct nfs4_slot_table *tbl;
 	int max_slots;
 
 	if (ses == NULL)
 		return;
+	tbl = &ses->fc_slot_table;
 	if (test_and_clear_bit(NFS4_SESSION_DRAINING, &ses->session_state)) {
-		spin_lock(&ses->fc_slot_table.slot_tbl_lock);
-		max_slots = ses->fc_slot_table.max_slots;
+		spin_lock(&tbl->slot_tbl_lock);
+		max_slots = tbl->max_slots;
 		while (max_slots--) {
-			struct rpc_task *task;
-
-			task = rpc_wake_up_next(&ses->fc_slot_table.
-						slot_tbl_waitq);
-			if (!task)
+			if (rpc_wake_up_first(&tbl->slot_tbl_waitq,
+						nfs4_set_task_privileged,
+						NULL) == NULL)
 				break;
-			rpc_task_set_priority(task, RPC_PRIORITY_PRIVILEGED);
 		}
-		spin_unlock(&ses->fc_slot_table.slot_tbl_lock);
+		spin_unlock(&tbl->slot_tbl_lock);
 	}
 }