ovl: decide if revalidate needed on a per-dentry basis

Allow completely skipping ->revalidate() on a per-dentry basis, in case the
underlying layers used for a dentry do not themselves have ->revalidate().

E.g. negative overlay dentry has no underlying layers, hence revalidate is
unnecessary.  Or if lower layer is remote but overlay dentry is pure-upper,
then can skip revalidate.

The following places need to update whether the dentry needs revalidate or
not:

 - fill-super (root dentry)
 - lookup
 - create
 - fh_to_dentry
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/dir.c

@@ -243,6 +243,9 @@ static int ovl_instantiate(struct dentry *dentry, struct inode *inode,
 
 	ovl_dir_modified(dentry->d_parent, false);
 	ovl_dentry_set_upper_alias(dentry);
+	ovl_dentry_update_reval(dentry, newdentry,
+			DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE);
+
 	if (!hardlink) {
 		/*
 		 * ovl_obtain_alias() can be called after ovl_create_real()

fs/overlayfs/export.c

@@ -324,6 +324,8 @@ static struct dentry *ovl_obtain_alias(struct super_block *sb,
 		if (upper_alias)
 			ovl_dentry_set_upper_alias(dentry);
 	}
+	ovl_dentry_update_reval(dentry, upper,
+			DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE);
 
 	return d_instantiate_anon(dentry, inode);
 

fs/overlayfs/namei.c

@@ -1077,6 +1077,9 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 			goto out_free_oe;
 	}
 
+	ovl_dentry_update_reval(dentry, upperdentry,
+			DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE);
+
 	revert_creds(old_cred);
 	if (origin_path) {
 		dput(origin_path->dentry);

fs/overlayfs/overlayfs.h

@@ -230,6 +230,8 @@ bool ovl_index_all(struct super_block *sb);
 bool ovl_verify_lower(struct super_block *sb);
 struct ovl_entry *ovl_alloc_entry(unsigned int numlower);
 bool ovl_dentry_remote(struct dentry *dentry);
+void ovl_dentry_update_reval(struct dentry *dentry, struct dentry *upperdentry,
+			     unsigned int mask);
 bool ovl_dentry_weird(struct dentry *dentry);
 enum ovl_path_type ovl_path_type(struct dentry *dentry);
 void ovl_path_upper(struct dentry *dentry, struct path *path);

fs/overlayfs/super.c

@@ -158,11 +158,6 @@ static int ovl_dentry_weak_revalidate(struct dentry *dentry, unsigned int flags)
 static const struct dentry_operations ovl_dentry_operations = {
 	.d_release = ovl_dentry_release,
 	.d_real = ovl_d_real,
-};
-
-static const struct dentry_operations ovl_reval_dentry_operations = {
-	.d_release = ovl_dentry_release,
-	.d_real = ovl_d_real,
 	.d_revalidate = ovl_dentry_revalidate,
 	.d_weak_revalidate = ovl_dentry_weak_revalidate,
 };
@@ -779,7 +774,7 @@ static int ovl_check_namelen(struct path *path, struct ovl_fs *ofs,
 }
 
 static int ovl_lower_dir(const char *name, struct path *path,
-			 struct ovl_fs *ofs, int *stack_depth, bool *remote)
+			 struct ovl_fs *ofs, int *stack_depth)
 {
 	int fh_type;
 	int err;
@@ -794,9 +789,6 @@ static int ovl_lower_dir(const char *name, struct path *path,
 
 	*stack_depth = max(*stack_depth, path->mnt->mnt_sb->s_stack_depth);
 
-	if (ovl_dentry_remote(path->dentry))
-		*remote = true;
-
 	/*
 	 * The inodes index feature and NFS export need to encode and decode
 	 * file handles, so they require that all layers support them.
@@ -1441,7 +1433,6 @@ static struct ovl_entry *ovl_get_lowerstack(struct super_block *sb,
 	char *lowertmp, *lower;
 	struct path *stack = NULL;
 	unsigned int stacklen, numlower = 0, i;
-	bool remote = false;
 	struct ovl_entry *oe;
 
 	err = -ENOMEM;
@@ -1473,7 +1464,7 @@ static struct ovl_entry *ovl_get_lowerstack(struct super_block *sb,
 	lower = lowertmp;
 	for (numlower = 0; numlower < stacklen; numlower++) {
 		err = ovl_lower_dir(lower, &stack[numlower], ofs,
-				    &sb->s_stack_depth, &remote);
+				    &sb->s_stack_depth);
 		if (err)
 			goto out_err;
 
@@ -1501,11 +1492,6 @@ static struct ovl_entry *ovl_get_lowerstack(struct super_block *sb,
 		oe->lowerstack[i].layer = &ofs->layers[i+1];
 	}
 
-	if (remote)
-		sb->s_d_op = &ovl_reval_dentry_operations;
-	else
-		sb->s_d_op = &ovl_dentry_operations;
-
 out:
 	for (i = 0; i < numlower; i++)
 		path_put(&stack[i]);
@@ -1623,6 +1609,7 @@ static struct dentry *ovl_get_root(struct super_block *sb,
 	ovl_dentry_set_flag(OVL_E_CONNECTED, root);
 	ovl_set_upperdata(d_inode(root));
 	ovl_inode_init(d_inode(root), &oip, ino, fsid);
+	ovl_dentry_update_reval(root, upperdentry, DCACHE_OP_WEAK_REVALIDATE);
 
 	return root;
 }
@@ -1636,6 +1623,8 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 	struct cred *cred;
 	int err;
 
+	sb->s_d_op = &ovl_dentry_operations;
+
 	err = -ENOMEM;
 	ofs = kzalloc(sizeof(struct ovl_fs), GFP_KERNEL);
 	if (!ofs)

fs/overlayfs/util.c

@@ -96,6 +96,21 @@ bool ovl_dentry_remote(struct dentry *dentry)
 		(DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE);
 }
 
+void ovl_dentry_update_reval(struct dentry *dentry, struct dentry *upperdentry,
+			     unsigned int mask)
+{
+	struct ovl_entry *oe = OVL_E(dentry);
+	unsigned int i, flags = 0;
+
+	for (i = 0; i < oe->numlower; i++)
+		flags |= oe->lowerstack[i].dentry->d_flags;
+
+	spin_lock(&dentry->d_lock);
+	dentry->d_flags &= ~mask;
+	dentry->d_flags |= flags & mask;
+	spin_unlock(&dentry->d_lock);
+}
+
 bool ovl_dentry_weird(struct dentry *dentry)
 {
 	return dentry->d_flags & (DCACHE_NEED_AUTOMOUNT |