bcachefs: bch2_ioctl_subvolume_destroy() fixes

bch2_evict_subvolume_inodes() was getting stuck - due to incorrectly
pruning the dcache.

Also, fix missing permissions checks.

Reported-by: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Author: Kent Overstreet

fs/bcachefs/fs-ioctl.c

@@ -541,10 +541,12 @@ static long bch2_ioctl_subvolume_destroy(struct bch_fs *c, struct file *filp,
 		ret = -ENOENT;
 		goto err;
 	}
-	ret = __bch2_unlink(dir, victim, true);
+
+	ret =   inode_permission(file_mnt_idmap(filp), d_inode(victim), MAY_WRITE) ?:
+		__bch2_unlink(dir, victim, true);
 	if (!ret) {
 		fsnotify_rmdir(dir, victim);
-		d_delete(victim);
+		d_invalidate(victim);
 	}
 err:
 	inode_unlock(dir);