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

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Message-ID: <20190703175845.GA68011@archlinux-epyc>
Date:   Wed, 3 Jul 2019 10:58:45 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: Re: [PATCH] waitqueue: fix clang -Wuninitialized warnings

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>

Thank you for sending the fix for these warnings, they are the last
major ones that I can see across various defconfig and allyesconfig
testing. This resolves all of them.

Reviewed-by: Nathan Chancellor <natechancellor@...il.com>
Tested-by: Nathan Chancellor <natechancellor@...il.com>