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

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Date:   Mon, 25 Mar 2019 17:24:58 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     James Bottomley <James.Bottomley@...senpartnership.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Jens Axboe <axboe@...nel.dk>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Hannes Reinecke <hare@...e.com>,
        Matthew Wilcox <willy@...radead.org>,
        David Hildenbrand <david@...hat.com>,
        Nikolay Borisov <nborisov@...e.com>,
        linux-block <linux-block@...r.kernel.org>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] io_uring: fix big-endian compat signal mask handling

On Mon, Mar 25, 2019 at 5:19 PM James Bottomley
<James.Bottomley@...senpartnership.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