Re: [PATCH 1/2] io_uring: fix big-endian compat signal mask handling

[Arnd Bergmann <arnd@arndb.de>]

On Mon, Mar 25, 2019 at 5:19 PM James Bottomley
<James.Bottomley@hansenpartnership.com> wrote:

> > --- a/fs/io_uring.c
> > +++ b/fs/io_uring.c
> > @@ -1968,7 +1968,15 @@ static int io_cqring_wait(struct io_ring_ctx
> > *ctx, int min_events,
> >               return 0;
> >
> >       if (sig) {
> > -             ret = set_user_sigmask(sig, &ksigmask, &sigsaved,
> > sigsz);
> > +#ifdef CONFIG_COMPAT
> > +             if (in_compat_syscall())
> > +                     ret = set_compat_user_sigmask((const
> > compat_sigset_t __user *)sig,
> > +                                                   &ksigmask,
> > &sigsaved, sigsz);
> > +             else
> > +#endif
>
> This looks a bit suboptimal: shouldn't in_compat_syscall() be hard
> coded to return 0 if CONFIG_COMPAT isn't defined?  That way the
> compiler can do the correct optimization and we don't have to litter
> #ifdefs and worry about undefined variables and other things.

The check can be outside of the #ifdef, but set_compat_user_sigmask
is not declared then.

I think for the future we can consider just moving the compat logic
into set_user_sigmask(), which would simplify most of the callers,
but that seemed to invasive as a bugfix for 5.1.

      Arnd