On Sun, Oct 06, 2024 at 10:04:26PM +0100, Al Viro wrote:
> 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?
read() from metacopied file after fsync(), with the data still in lower
layer? Or am I misreading that?
