[PATCH v3 24/25] sunrpc: Change how dentry's d_lock field is accessed

Because of the changes made in dcache.h header file, files that
use the d_lock field of the dentry structure need to be changed
accordingly. All the d_lock's spin_lock() and spin_unlock() calls
are replaced by the corresponding d_lock() and d_unlock() calls.
There is no change in logic and everything should just work.

Signed-off-by: Waiman Long <redacted>
---
 net/sunrpc/rpc_pipe.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/sunrpc/rpc_pipe.c b/net/sunrpc/rpc_pipe.c
index e7ce4b3..58bc128 100644
--- a/net/sunrpc/rpc_pipe.c
+++ b/net/sunrpc/rpc_pipe.c

@@ -427,14 +427,14 @@ rpc_info_open(struct inode *inode, struct file *file)
 	if (!ret) {
 		struct seq_file *m = file->private_data;
 
-		spin_lock(&file->f_path.dentry->d_lock);
+		d_lock(file->f_path.dentry);
 		if (!d_unhashed(file->f_path.dentry))
 			clnt = RPC_I(inode)->private;
 		if (clnt != NULL && atomic_inc_not_zero(&clnt->cl_count)) {
-			spin_unlock(&file->f_path.dentry->d_lock);
+			d_unlock(file->f_path.dentry);
 			m->private = clnt;
 		} else {
-			spin_unlock(&file->f_path.dentry->d_lock);
+			d_unlock(file->f_path.dentry);
 			single_release(inode, file);
 			ret = -EINVAL;
 		}

-- 
1.7.1

On Wed, Jul 03, 2013 at 04:25:32PM -0400, Waiman Long wrote:

There is no change in logic and everything should just work.

-		spin_lock(&file->f_path.dentry->d_lock);
+		d_lock(file->f_path.dentry);
 		if (!d_unhashed(file->f_path.dentry))
 			clnt = RPC_I(inode)->private;
 		if (clnt != NULL && atomic_inc_not_zero(&clnt->cl_count)) {
-			spin_unlock(&file->f_path.dentry->d_lock);
+			d_unlock(file->f_path.dentry);

Could somebody explain WTF is being protected here?  It's not ->private -
that gets set (and, more importantly, cleared) without ->d_lock in sight.
Trond, that seems to be your code from about three years ago (introduced
in "SUNRPC: Fix a race in rpc_info_open").  What's going on there?

On Thu, 2013-07-04 at 05:20 +0100, Al Viro wrote:

On Wed, Jul 03, 2013 at 04:25:32PM -0400, Waiman Long wrote:

quoted

There is no change in logic and everything should just work.

quoted

-		spin_lock(&file->f_path.dentry->d_lock);
+		d_lock(file->f_path.dentry);
 		if (!d_unhashed(file->f_path.dentry))
 			clnt = RPC_I(inode)->private;
 		if (clnt != NULL && atomic_inc_not_zero(&clnt->cl_count)) {
-			spin_unlock(&file->f_path.dentry->d_lock);
+			d_unlock(file->f_path.dentry);

Could somebody explain WTF is being protected here?  It's not ->private -
that gets set (and, more importantly, cleared) without ->d_lock in sight.
Trond, that seems to be your code from about three years ago (introduced
in "SUNRPC: Fix a race in rpc_info_open").  What's going on there?

AFAICR we're using the fact that the dentry will remain hashed until
we're in the process of freeing up the rpc_client. By testing that the
dentry is hashed under the dentry->d_lock, we are assured that the
non-NULL 'clnt' is still pointing to a valid rpc_client, and that it is
safe to access clnt->cl_count.

-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@netapp.com
www.netapp.com