Re: [PATCH 4/9] rpc: add an rpc_pipe_open method

["J. Bruce Fields" <bfields@fieldses.org>]

On Mon, Nov 10, 2008 at 03:37:57PM -0500, bfields wrote:
> On Mon, Nov 10, 2008 at 03:35:22PM -0500, Trond Myklebust wrote:
> > BTW: This is racy. You have to set first_open _after_ you take the
> > inode->i_mutex.
> 
> Whoops!  Good catch, thanks--fixed.

(Updated version follows.)

--b.

commit 7f5c491a32857dc8ba587cc365a2d70024f7b33e
Author: J. Bruce Fields <bfields@citi.umich.edu>
Date:   Fri Nov 7 18:53:24 2008 -0500

    rpc: call release_pipe only on last close
    
    I can't see any reason we need to call this until either the kernel or
    the last gssd closes the pipe.
    
    Also, this allows to guarantee that open_pipe and release_pipe are
    called strictly in pairs; open_pipe on gssd's first open, release_pipe
    on gssd's last close (or on the close of the kernel side of the pipe, if
    that comes first).
    
    That will make it very easy for the gss code to keep track of which
    pipes gssd is using.
    
    Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

diff --git a/net/sunrpc/rpc_pipe.c b/net/sunrpc/rpc_pipe.c
index 4171ab7..f734103 100644
--- a/net/sunrpc/rpc_pipe.c
+++ b/net/sunrpc/rpc_pipe.c
@@ -126,13 +126,14 @@ rpc_close_pipes(struct inode *inode)
 {
 	struct rpc_inode *rpci = RPC_I(inode);
 	struct rpc_pipe_ops *ops;
+	int still_open;
 
 	mutex_lock(&inode->i_mutex);
 	ops = rpci->ops;
 	if (ops != NULL) {
 		LIST_HEAD(free_list);
-
 		spin_lock(&inode->i_lock);
+		still_open = rpci->nreaders != 0 || rpci->nwriters != 0;
 		rpci->nreaders = 0;
 		list_splice_init(&rpci->in_upcall, &free_list);
 		list_splice_init(&rpci->pipe, &free_list);
@@ -141,7 +142,7 @@ rpc_close_pipes(struct inode *inode)
 		spin_unlock(&inode->i_lock);
 		rpc_purge_list(rpci, &free_list, ops->destroy_msg, -EPIPE);
 		rpci->nwriters = 0;
-		if (ops->release_pipe)
+		if (still_open && ops->release_pipe)
 			ops->release_pipe(inode);
 		cancel_delayed_work_sync(&rpci->queue_timeout);
 	}
@@ -169,12 +170,13 @@ static int
 rpc_pipe_open(struct inode *inode, struct file *filp)
 {
 	struct rpc_inode *rpci = RPC_I(inode);
-	int first_open = rpci->nreaders == 0 && rpci->nwriters == 0;
+	int first_open;
 	int res = -ENXIO;
 
 	mutex_lock(&inode->i_mutex);
 	if (rpci->ops == NULL)
 		goto out;
+	first_open = rpci->nreaders == 0 && rpci->nwriters == 0;
 	if (first_open && rpci->ops->open_pipe) {
 		res = rpci->ops->open_pipe(inode);
 		if (res)
@@ -195,6 +197,7 @@ rpc_pipe_release(struct inode *inode, struct file *filp)
 {
 	struct rpc_inode *rpci = RPC_I(inode);
 	struct rpc_pipe_msg *msg;
+	int last_close;
 
 	mutex_lock(&inode->i_mutex);
 	if (rpci->ops == NULL)
@@ -221,7 +224,8 @@ rpc_pipe_release(struct inode *inode, struct file *filp)
 					rpci->ops->destroy_msg, -EAGAIN);
 		}
 	}
-	if (rpci->ops->release_pipe)
+	last_close = rpci->nwriters == 0 && rpci->nreaders == 0;
+	if (last_close && rpci->ops->release_pipe)
 		rpci->ops->release_pipe(inode);
 out:
 	mutex_unlock(&inode->i_mutex);