[patch] add dentry revalidate to follow mount.

[pravin shelar <Pravin.Shelar@xxxxxxx>]

Hi
         i have seen error in lustre while setting permission on fs root
from a client. problem is permission are not getting propagated to
other clients.

this is because of do_lookup() call path which does not revalidate
fs root dentry in follow_mount()

attached patch adds revalidation call in follow_mount.

Thanks,
Pravin

Signed-off-by: pravin shelar <pravin.shelar@xxxxxxx>

Index: linux-2.6-latest/fs/namei.c
===================================================================
--- linux-2.6-latest.orig/fs/namei.c
+++ linux-2.6-latest/fs/namei.c
@@ -691,9 +691,11 @@ int follow_up(struct vfsmount **mnt, str
 /* no need for dcache_lock, as serialization is taken care in
  * namespace.c
  */
-static int __follow_mount(struct path *path)
+static int __follow_mount(struct nameidata *nd, struct path *path)
 {
 	int res = 0;
+	struct dentry *dentry;
+
 	while (d_mountpoint(path->dentry)) {
 		struct vfsmount *mounted = lookup_mnt(path->mnt, path->dentry);
 		if (!mounted)
@@ -703,6 +705,18 @@ static int __follow_mount(struct path *p
 			mntput(path->mnt);
 		path->mnt = mounted;
 		path->dentry = dget(mounted->mnt_root);
+		dentry = path->dentry;
+
+		if (dentry->d_op && dentry->d_op->d_revalidate){
+			dentry = do_revalidate(dentry, nd);
+			if (!dentry)
+				return -EINVAL;
+			if (IS_ERR(dentry))
+				return PTR_ERR(dentry);
+		}
+
+		path->dentry = dentry;
+
 		res = 1;
 	}
 	return res;
@@ -788,6 +802,7 @@ static int do_lookup(struct nameidata *n
 {
 	struct vfsmount *mnt = nd->path.mnt;
 	struct dentry *dentry = __d_lookup(nd->path.dentry, name);
+	int rc;
 
 	if (!dentry)
 		goto need_lookup;
@@ -796,7 +811,9 @@ static int do_lookup(struct nameidata *n
 done:
 	path->mnt = mnt;
 	path->dentry = dentry;
-	__follow_mount(path);
+	rc = __follow_mount(nd, path);
+	if (rc < 0)
+		return rc;
 	return 0;
 
 need_lookup:
@@ -1747,11 +1764,15 @@ do_last:
 	if (flag & O_EXCL)
 		goto exit_dput;
 
-	if (__follow_mount(&path)) {
-		error = -ELOOP;
-		if (flag & O_NOFOLLOW)
+	error = __follow_mount(&nd, &path);
+	if (error == 1) {
+		if (flag & O_NOFOLLOW) {
+			error = -ELOOP;
 			goto exit_dput;
+		}
 	}
+	if (error < 0)
+		goto exit_dput;
 
 	error = -ENOENT;
 	if (!path.dentry->d_inode)