ramfs: fix double freeing s_fs_info on failed mount

If ramfs mount fails, s_fs_info will be freed twice in ramfs_fill_super()
and ramfs_kill_sb(), leading to kernel oops.

Consolidate and beautify the code.
Make sure s_fs_info and s_root are in known good states.
Acked-by: NWu Fengguang <fengguang.wu@intel.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

fs/ramfs/inode.c

@@ -221,11 +221,11 @@ static int ramfs_fill_super(struct super_block * sb, void * data, int silent)
 	save_mount_options(sb, data);
 
 	fsi = kzalloc(sizeof(struct ramfs_fs_info), GFP_KERNEL);
+	sb->s_fs_info = fsi;
 	if (!fsi) {
 		err = -ENOMEM;
 		goto fail;
 	}
-	sb->s_fs_info = fsi;
 
 	err = ramfs_parse_options(data, &fsi->mount_opts);
 	if (err)
@@ -237,6 +237,7 @@ static int ramfs_fill_super(struct super_block * sb, void * data, int silent)
 	sb->s_magic		= RAMFS_MAGIC;
 	sb->s_op		= &ramfs_ops;
 	sb->s_time_gran		= 1;
+
 	inode = ramfs_get_inode(sb, S_IFDIR | fsi->mount_opts.mode, 0);
 	if (!inode) {
 		err = -ENOMEM;
@@ -244,14 +245,16 @@ static int ramfs_fill_super(struct super_block * sb, void * data, int silent)
 	}
 
 	root = d_alloc_root(inode);
+	sb->s_root = root;
 	if (!root) {
 		err = -ENOMEM;
 		goto fail;
 	}
-	sb->s_root = root;
+
 	return 0;
 fail:
 	kfree(fsi);
+	sb->s_fs_info = NULL;
 	iput(inode);
 	return err;
 }