nfsd: fix a warning in __cld_pipe_upcall()

BugLink: https://bugs.launchpad.net/bugs/1858489

[ Upstream commit b493fd31 ]

__cld_pipe_upcall() emits a "do not call blocking ops when
!TASK_RUNNING" warning due to the dput() call in rpc_queue_upcall().
Fix it by using a completion instead of hand coding the wait.
Signed-off-by: Scott Mayhew <smayhew@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

fs/nfsd/nfs4recover.c

@@ -655,7 +655,7 @@ struct cld_net {
 struct cld_upcall {
 	struct list_head	 cu_list;
 	struct cld_net		*cu_net;
-	struct task_struct	*cu_task;
+	struct completion	 cu_done;
 	struct cld_msg		 cu_msg;
 };
 
@@ -664,23 +664,18 @@ __cld_pipe_upcall(struct rpc_pipe *pipe, struct cld_msg *cmsg)
 {
 	int ret;
 	struct rpc_pipe_msg msg;
+	struct cld_upcall *cup = container_of(cmsg, struct cld_upcall, cu_msg);
 
 	memset(&msg, 0, sizeof(msg));
 	msg.data = cmsg;
 	msg.len = sizeof(*cmsg);
 
-	/*
-	 * Set task state before we queue the upcall. That prevents
-	 * wake_up_process in the downcall from racing with schedule.
-	 */
-	set_current_state(TASK_UNINTERRUPTIBLE);
 	ret = rpc_queue_upcall(pipe, &msg);
 	if (ret < 0) {
-		set_current_state(TASK_RUNNING);
 		goto out;
 	}
 
-	schedule();
+	wait_for_completion(&cup->cu_done);
 
 	if (msg.errno < 0)
 		ret = msg.errno;
@@ -747,7 +742,7 @@ cld_pipe_downcall(struct file *filp, const char __user *src, size_t mlen)
 	if (copy_from_user(&cup->cu_msg, src, mlen) != 0)
 		return -EFAULT;
 
-	wake_up_process(cup->cu_task);
+	complete(&cup->cu_done);
 	return mlen;
 }
 
@@ -762,7 +757,7 @@ cld_pipe_destroy_msg(struct rpc_pipe_msg *msg)
 	if (msg->errno >= 0)
 		return;
 
-	wake_up_process(cup->cu_task);
+	complete(&cup->cu_done);
 }
 
 static const struct rpc_pipe_ops cld_upcall_ops = {
@@ -893,7 +888,7 @@ alloc_cld_upcall(struct cld_net *cn)
 			goto restart_search;
 		}
 	}
-	new->cu_task = current;
+	init_completion(&new->cu_done);
 	new->cu_msg.cm_vers = CLD_UPCALL_VERSION;
 	put_unaligned(cn->cn_xid++, &new->cu_msg.cm_xid);
 	new->cu_net = cn;