On Sun, Oct 06, 2024 at 10:23:57AM +0200, Amir Goldstein wrote:
> + /*
> + * Usually, if we operated on a stashed upperfile once, all following
> + * operations will operate on the stashed upperfile, but there is one
> + * exception - ovl_fsync(datasync = false) can populate the stashed
> + * upperfile to perform fsync on upper metadata inode. In this case,
> + * following read/write operations will not use the stashed upperfile.
> + */
> + if (upperfile && likely(ovl_is_real_file(upperfile, realpath))) {
> + realfile = upperfile;
> + goto checkflags;
> }
>
> + /*
> + * If realfile is lower and has been copied up since we'd opened it,
> + * open the real upper file and stash it in backing_file_private().
> + */
> + if (unlikely(!ovl_is_real_file(realfile, realpath))) {
> + struct file *old;
> +
> + /* Either stashed realfile or upperfile must match realinode */
> + if (WARN_ON_ONCE(upperfile))
> + return -EIO;
> +
> + upperfile = ovl_open_realfile(file, realpath);
> + if (IS_ERR(upperfile))
> + return PTR_ERR(upperfile);
> +
> + old = cmpxchg_release(backing_file_private_ptr(realfile), NULL,
> + upperfile);
> + if (old) {
> + fput(upperfile);
> + upperfile = old;
> + }
> +
> + /* Stashed upperfile that won the race must match realinode */
> + if (WARN_ON_ONCE(!ovl_is_real_file(upperfile, realpath)))
> + return -EIO;
> +
> + realfile = upperfile;
> + }
> +
> +checkflags:
Hmm... That still feels awkward. Question: can we reach that code with
* non-NULL upperfile
* false ovl_is_real_file(upperfile, realpath)
* true ovl_is_real_file(realfile, realpath)
Is that really possible?
