SUNRPC: fix pipe->ops cleanup on pipe dentry unlink

This patch looks late due to GSS AUTH patches sent already. But it fixes a flaw
in RPC PipeFS pipes handling.
I've added this patch in the series, because this series related to pipes. But
it should be a part of previous series named "SUNPRC: cleanup PipeFS for
network-namespace-aware users".

Pipe dentry can be created and destroyed many times during pipe life cycle.
This actually means, that we can't set pipe->ops to NULL in rpc_close_pipes()
and use this variable as a flag, indicating, that pipe's dentry is unlinking.
To follow this restriction, this patch replaces "pipe->ops = NULL" assignment
and checks for NULL with "pipe->dentry = NULL" assignment and checks for
NULL respectively.
This patch also removes check for non-NULL pipe->ops (or pipe->dentry) in
rpc_close_pipes() because it always non-NULL now.
Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

net/sunrpc/rpc_pipe.c

@@ -86,10 +86,6 @@ rpc_timeout_upcall_queue(struct work_struct *work)
 	void (*destroy_msg)(struct rpc_pipe_msg *);
 
 	spin_lock(&pipe->lock);
-	if (pipe->ops == NULL) {
-		spin_unlock(&pipe->lock);
-		return;
-	}
 	destroy_msg = pipe->ops->destroy_msg;
 	if (pipe->nreaders == 0) {
 		list_splice_init(&pipe->pipe, &free_list);
@@ -135,8 +131,6 @@ rpc_queue_upcall(struct rpc_pipe *pipe, struct rpc_pipe_msg *msg)
 	int res = -EPIPE;
 
 	spin_lock(&pipe->lock);
-	if (pipe->ops == NULL)
-		goto out;
 	if (pipe->nreaders) {
 		list_add_tail(&msg->list, &pipe->pipe);
 		pipe->pipelen += msg->len;
@@ -150,7 +144,6 @@ rpc_queue_upcall(struct rpc_pipe *pipe, struct rpc_pipe_msg *msg)
 		pipe->pipelen += msg->len;
 		res = 0;
 	}
-out:
 	spin_unlock(&pipe->lock);
 	wake_up(&pipe->waitq);
 	return res;
@@ -167,27 +160,23 @@ static void
 rpc_close_pipes(struct inode *inode)
 {
 	struct rpc_pipe *pipe = RPC_I(inode)->pipe;
-	const struct rpc_pipe_ops *ops;
 	int need_release;
+	LIST_HEAD(free_list);
 
 	mutex_lock(&inode->i_mutex);
-	ops = pipe->ops;
-	if (ops != NULL) {
-		LIST_HEAD(free_list);
 	spin_lock(&pipe->lock);
 	need_release = pipe->nreaders != 0 || pipe->nwriters != 0;
 	pipe->nreaders = 0;
 	list_splice_init(&pipe->in_upcall, &free_list);
 	list_splice_init(&pipe->pipe, &free_list);
 	pipe->pipelen = 0;
-		pipe->ops = NULL;
+	pipe->dentry = NULL;
 	spin_unlock(&pipe->lock);
-		rpc_purge_list(pipe, &free_list, ops->destroy_msg, -EPIPE);
+	rpc_purge_list(pipe, &free_list, pipe->ops->destroy_msg, -EPIPE);
 	pipe->nwriters = 0;
-		if (need_release && ops->release_pipe)
-			ops->release_pipe(inode);
+	if (need_release && pipe->ops->release_pipe)
+		pipe->ops->release_pipe(inode);
 	cancel_delayed_work_sync(&pipe->queue_timeout);
-	}
 	rpc_inode_setowner(inode, NULL);
 	mutex_unlock(&inode->i_mutex);
 }
@@ -223,7 +212,7 @@ rpc_pipe_open(struct inode *inode, struct file *filp)
 	int res = -ENXIO;
 
 	mutex_lock(&inode->i_mutex);
-	if (pipe->ops == NULL)
+	if (pipe->dentry == NULL)
 		goto out;
 	first_open = pipe->nreaders == 0 && pipe->nwriters == 0;
 	if (first_open && pipe->ops->open_pipe) {
@@ -249,7 +238,7 @@ rpc_pipe_release(struct inode *inode, struct file *filp)
 	int last_close;
 
 	mutex_lock(&inode->i_mutex);
-	if (pipe->ops == NULL)
+	if (pipe->dentry == NULL)
 		goto out;
 	msg = filp->private_data;
 	if (msg != NULL) {
@@ -290,7 +279,7 @@ rpc_pipe_read(struct file *filp, char __user *buf, size_t len, loff_t *offset)
 	int res = 0;
 
 	mutex_lock(&inode->i_mutex);
-	if (pipe->ops == NULL) {
+	if (pipe->dentry == NULL) {
 		res = -EPIPE;
 		goto out_unlock;
 	}
@@ -333,7 +322,7 @@ rpc_pipe_write(struct file *filp, const char __user *buf, size_t len, loff_t *of
 
 	mutex_lock(&inode->i_mutex);
 	res = -EPIPE;
-	if (pipe->ops != NULL)
+	if (pipe->dentry != NULL)
 		res = pipe->ops->downcall(filp, buf, len);
 	mutex_unlock(&inode->i_mutex);
 	return res;
@@ -348,7 +337,7 @@ rpc_pipe_poll(struct file *filp, struct poll_table_struct *wait)
 	poll_wait(filp, &pipe->waitq, wait);
 
 	mask = POLLOUT | POLLWRNORM;
-	if (pipe->ops == NULL)
+	if (pipe->dentry == NULL)
 		mask |= POLLERR | POLLHUP;
 	if (filp->private_data || !list_empty(&pipe->pipe))
 		mask |= POLLIN | POLLRDNORM;
@@ -365,7 +354,7 @@ rpc_pipe_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 	switch (cmd) {
 	case FIONREAD:
 		spin_lock(&pipe->lock);
-		if (pipe->ops == NULL) {
+		if (pipe->dentry == NULL) {
 			spin_unlock(&pipe->lock);
 			return -EPIPE;
 		}