NFS: Fix a jiffie wraparound issue

dentry verifiers are always set to the parent directory's
cache_change_attribute. There is no reason to be testing for anything other
than equality when we're trying to find out if the dentry has been checked
since the last time the directory was modified.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/dir.c

@@ -650,12 +650,17 @@ int nfs_fsync_dir(struct file *filp, struct dentry *dentry, int datasync)
  */
 static int nfs_check_verifier(struct inode *dir, struct dentry *dentry)
 {
+	unsigned long verf;
+
 	if (IS_ROOT(dentry))
 		return 1;
+	verf = (unsigned long)dentry->d_fsdata;
 	if ((NFS_I(dir)->cache_validity & NFS_INO_INVALID_ATTR) != 0
-			|| nfs_attribute_timeout(dir))
+			|| nfs_attribute_timeout(dir)
+			|| nfs_caches_unstable(dir)
+			|| verf != NFS_I(dir)->cache_change_attribute)
 		return 0;
-	return nfs_verify_change_attribute(dir, (unsigned long)dentry->d_fsdata);
+	return 1;
 }
 
 static inline void nfs_set_verifier(struct dentry * dentry, unsigned long verf)
@@ -665,7 +670,6 @@ static inline void nfs_set_verifier(struct dentry * dentry, unsigned long verf)
 
 static void nfs_refresh_verifier(struct dentry * dentry, unsigned long verf)
 {
-	if (time_after(verf, (unsigned long)dentry->d_fsdata))
 	nfs_set_verifier(dentry, verf);
 }