[PATCH v2] NFS: Don't skip lookup when holding a delegation

[Benjamin Coddington <bcodding@redhat.com>]

If we skip lookup revalidation while holding a delegation, we might miss
that the file has changed directories on the server.  The directory's
change attribute should still be checked against the dentry's d_time to
perform a complete revalidation.

V2 - Add some commentary as suggested-by J. Bruce Fields.

Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
---
 fs/nfs/dir.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index 0adfd8840110..8723e82f5c9d 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1197,12 +1197,20 @@ nfs_do_lookup_revalidate(struct inode *dir, struct dentry *dentry,
 		goto out_bad;
 	}
 
-	if (NFS_PROTO(dir)->have_delegation(inode, FMODE_READ))
-		return nfs_lookup_revalidate_delegated(dir, dentry, inode);
-
 	/* Force a full look up iff the parent directory has changed */
 	if (!(flags & (LOOKUP_EXCL | LOOKUP_REVAL)) &&
 	    nfs_check_verifier(dir, dentry, flags & LOOKUP_RCU)) {
+
+		/*
+		 * Note that the file can't move while we hold a
+		 * delegation.  But this dentry could have been cached
+		 * before we got a delegation.  So it's only safe to
+		 * skip revalidation when the parent directory is
+		 * unchanged:
+		 */
+		if (NFS_PROTO(dir)->have_delegation(inode, FMODE_READ))
+			return nfs_lookup_revalidate_delegated(dir, dentry, inode);
+
 		error = nfs_lookup_verify_inode(inode, flags);
 		if (error) {
 			if (error == -ESTALE)
@@ -1635,9 +1643,6 @@ nfs4_do_lookup_revalidate(struct inode *dir, struct dentry *dentry,
 	if (inode == NULL)
 		goto full_reval;
 
-	if (NFS_PROTO(dir)->have_delegation(inode, FMODE_READ))
-		return nfs_lookup_revalidate_delegated(dir, dentry, inode);
-
 	/* NFS only supports OPEN on regular files */
 	if (!S_ISREG(inode->i_mode))
 		goto full_reval;
-- 
2.20.1