linux-kernel - Re: [ammarfaizi2-block:google/android/kernel/common/android12-5.4 6517/9999] fs/userfaultfd.c:1519:9: warning: variable 'ioctls

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Date:   Wed, 19 Jan 2022 14:10:04 -0800
From:   Kalesh Singh <kaleshsingh@...gle.com>
To:     Axel Rasmussen <axelrasmussen@...gle.com>
Cc:     Suren Baghdasaryan <surenb@...gle.com>,
        kernel test robot <lkp@...el.com>, llvm@...ts.linux.dev,
        kbuild-all@...ts.01.org,
        "GNU/Weeb Mailing List" <gwml@...weeb.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Todd Kjos <tkjos@...gle.com>, Peter Xu <peterx@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Lokesh Gidra <lokeshgidra@...gle.com>
Subject: Re: [ammarfaizi2-block:google/android/kernel/common/android12-5.4
 6517/9999] fs/userfaultfd.c:1519:9: warning: variable 'ioctls_out' set but
 not used

On Wed, Jan 19, 2022 at 2:03 PM Axel Rasmussen <axelrasmussen@...gle.com> wrote:
>
> On Wed, Jan 19, 2022 at 1:19 PM Suren Baghdasaryan <surenb@...gle.com> wrote:
> >
> > On Wed, Jan 19, 2022 at 12:39 PM Axel Rasmussen
> > <axelrasmussen@...gle.com> wrote:
> > >
> > > Lokesh, I only spent a few moments looking, but my suspicion is that
> > > this is the result of an incomplete backport of these patches to the
> > > Android kernel?
> > >
> > > The UFFDIO_CONTINUE patches introduced ioctls_out since the
> > > computation of it got more complicated, and those same patches also
> > > modified the put_user() on line 1533 here to use ioctls_out. I think
> > > Android backported the first part, but left out the second?
> >
> > The backport https://android-review.googlesource.com/c/kernel/common/+/1652718
> > looks like a mixture of
> > 14819305e09fe4 ("userfaultfd: wp: declare _UFFDIO_WRITEPROTECT
> > conditionally") and f619147104c8 ("userfaultfd: add UFFDIO_CONTINUE
> > ioctl").
> > Not sure why it was done this way, maybe to minimize code changes
> > while backporting.
> > Simplest fix is probably to add __maybe_unused to ioctls_out declaration.
>
> Unfortunately, that doesn't quite do it. That would fix the warning,
> but the code in the original e-mail is still wrong: we incorrectly
> don't report the _UFFDIO_CONTINUE bit, unless we use the value we
> computed in ioctls_out.

I think what happened is that Axel's patch [1] depends on the patch
from Peter [2]. [1] was backported without the dependency and the
conflict resolutions aren't quite correct.

[1] https://lore.kernel.org/lkml/20210301222728.176417-5-axelrasmussen@google.com/
[2] https://lore.kernel.org/lkml/20200220163112.11409-18-peterx@redhat.com/

- Kalesh