linux-kernel - Re: [PATCH] waitqueue: fix clang -Wuninitialized warnings

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Message-ID: <CAK8P3a041S8KFTz4ZjmByDUTM9pDxsWi=hGPeamkFfn4B1dcxQ@mail.gmail.com>
Date:   Tue, 9 Jul 2019 21:27:17 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] waitqueue: fix clang -Wuninitialized warnings

On Wed, Jul 3, 2019 at 7:58 PM Nathan Chancellor
<natechancellor@...il.com> wrote:
> On Wed, Jul 03, 2019 at 10:10:55AM +0200, Arnd Bergmann wrote:
> > When CONFIG_LOCKDEP is set, every use of DECLARE_WAIT_QUEUE_HEAD_ONSTACK()
> > produces an annoying warning from clang, which is particularly annoying
> > for allmodconfig builds:
> >
> > fs/namei.c:1646:34: error: variable 'wq' is uninitialized when used within its own initialization [-Werror,-Wuninitialized]
> >         DECLARE_WAIT_QUEUE_HEAD_ONSTACK(wq);
> >                                         ^~
> > include/linux/wait.h:74:63: note: expanded from macro 'DECLARE_WAIT_QUEUE_HEAD_ONSTACK'
> >         struct wait_queue_head name = __WAIT_QUEUE_HEAD_INIT_ONSTACK(name)
> >                                ~~~~                                  ^~~~
> > include/linux/wait.h:72:33: note: expanded from macro '__WAIT_QUEUE_HEAD_INIT_ONSTACK'
> >         ({ init_waitqueue_head(&name); name; })
> >                                        ^~~~
> >
> > After playing with it for a while, I have found a way to rephrase the
> > macro in a way that should work well with both gcc and clang and not
> > produce this warning. The open-coded __WAIT_QUEUE_HEAD_INIT_ONSTACK
> > is a little more verbose than the original version by Peter Zijlstra,
> > but avoids the gcc-ism that suppresses warnings when assigning a
> > variable to itself.
> >
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Signed-off-by: Arnd Bergmann <arnd@...db.de>
>
> Reviewed-by: Nathan Chancellor <natechancellor@...il.com>
> Tested-by: Nathan Chancellor <natechancellor@...il.com>

Who would be the right person to pick this patch up for mainline?

I guess it may have to wait until the end of the merge window now,
but I'd still like this to be part of 4.3 and possibly backported to
the stable kernels as we build those with clang as well.

       Arnd