VFS: introduce end_creating_keep()

Occasionally the caller of end_creating() wants to keep using the dentry.
Rather then requiring them to dget() the dentry (when not an error)
before calling end_creating(), provide end_creating_keep() which does
this.

cachefiles and overlayfs make use of this.

Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: NeilBrown <neil@brown.name>
Link: https://patch.msgid.link/20251113002050.676694-16-neilb@ownmail.net
Tested-by: syzbot@syzkaller.appspotmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: neilbrown

fs/cachefiles/namei.c

@@ -155,8 +155,7 @@ struct dentry *cachefiles_get_directory(struct cachefiles_cache *cache,
 
 	/* Tell rmdir() it's not allowed to delete the subdir */
 	inode_lock(d_inode(subdir));
-	dget(subdir);
-	end_creating(subdir);
+	end_creating_keep(subdir);
 
 	if (!__cachefiles_mark_inode_in_use(NULL, d_inode(subdir))) {
 		pr_notice("cachefiles: Inode already in use: %pd (B=%lx)\n",

fs/overlayfs/dir.c

@@ -251,10 +251,7 @@ struct dentry *ovl_create_temp(struct ovl_fs *ofs, struct dentry *workdir,
 	if (IS_ERR(ret))
 		return ret;
 	ret = ovl_create_real(ofs, workdir, ret, attr);
-	if (!IS_ERR(ret))
-		dget(ret);
-	end_creating(ret);
-	return ret;
+	return end_creating_keep(ret);
 }
 
 static int ovl_set_opaque_xerr(struct dentry *dentry, struct dentry *upper,
@@ -364,8 +361,7 @@ static int ovl_create_upper(struct dentry *dentry, struct inode *inode,
 	if (IS_ERR(newdentry))
 		return PTR_ERR(newdentry);
 
-	dget(newdentry);
-	end_creating(newdentry);
+	end_creating_keep(newdentry);
 
 	if (ovl_type_merge(dentry->d_parent) && d_is_dir(newdentry) &&
 	    !ovl_allow_offline_changes(ofs)) {

fs/overlayfs/super.c

@@ -319,8 +319,7 @@ static struct dentry *ovl_workdir_create(struct ovl_fs *ofs,
 		};
 
 		if (work->d_inode) {
-			dget(work);
-			end_creating(work);
+			end_creating_keep(work);
 			if (persist)
 				return work;
 			err = -EEXIST;
@@ -336,9 +335,7 @@ static struct dentry *ovl_workdir_create(struct ovl_fs *ofs,
 		}
 
 		work = ovl_do_mkdir(ofs, dir, work, attr.ia_mode);
-		if (!IS_ERR(work))
-			dget(work);
-		end_creating(work);
+		end_creating_keep(work);
 		err = PTR_ERR(work);
 		if (IS_ERR(work))
 			goto out_err;
@@ -630,9 +627,7 @@ static struct dentry *ovl_lookup_or_create(struct ovl_fs *ofs,
 		if (!child->d_inode)
 			child = ovl_create_real(ofs, parent, child,
 						OVL_CATTR(mode));
-		if (!IS_ERR(child))
-			dget(child);
-		end_creating(child);
+		end_creating_keep(child);
 	}
 	dput(parent);
 

include/linux/namei.h

@@ -125,6 +125,28 @@ static inline void end_creating(struct dentry *child)
 	end_dirop(child);
 }
 
+/* end_creating_keep - finish action started with start_creating() and return result
+ * @child: dentry returned by start_creating() or vfs_mkdir()
+ *
+ * Unlock and return the child. This can be called after
+ * start_creating() whether that function succeeded or not,
+ * but it is not needed on failure.
+ *
+ * If vfs_mkdir() was called then the value returned from that function
+ * should be given for @child rather than the original dentry, as vfs_mkdir()
+ * may have provided a new dentry.
+ *
+ * Returns: @child, which may be a dentry or an error.
+ *
+ */
+static inline struct dentry *end_creating_keep(struct dentry *child)
+{
+	if (!IS_ERR(child))
+		dget(child);
+	end_dirop(child);
+	return child;
+}
+
 /**
  * end_removing - finish action started with start_removing
  * @child:  dentry returned by start_removing()