linux-kernel - Re: [PATCH -next] mm: Mark 'stack_vm_area' with __maybe

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Date:   Fri, 28 Dec 2018 09:58:04 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     YueHaibing <yuehaibing@...wei.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Andy Lutomirski <luto@...capital.net>,
        Will Drewry <wad@...omium.org>,
        Marcos Paulo de Souza <marcos.souza.org@...il.com>,
        David Windsor <dave@...lcore.net>,
        Roman Gushchin <guro@...com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Rik van Riel <riel@...riel.com>,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH -next] mm: Mark 'stack_vm_area' with __maybe_unused

On Fri 28-12-18 02:46:30, YueHaibing wrote:
> Fixes gcc '-Wunused-but-set-variable' warning when
> CONFIG_VMAP_STACK is not set:

Isn't this warning disabled? I can see the following
# These warnings generated too much noise in a regular build.
# Use make W=1 to enable them (see scripts/Makefile.extrawarn)
KBUILD_CFLAGS += -Wno-unused-but-set-variable

in the main makefile. IMHO this warning doesn't really give us much.

> 
> kernel/fork.c: In function 'dup_task_struct':
> kernel/fork.c:843:20: warning:
>  variable 'stack_vm_area' set but not used [-Wunused-but-set-variable]
> 
> Signed-off-by: YueHaibing <yuehaibing@...wei.com>
> ---
>  kernel/fork.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/fork.c b/kernel/fork.c
> index e2a5156..b38c392 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -840,7 +840,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
>  {
>  	struct task_struct *tsk;
>  	unsigned long *stack;
> -	struct vm_struct *stack_vm_area;
> +	struct vm_struct *stack_vm_area __maybe_unused;
>  	int err;
>  
>  	if (node == NUMA_NO_NODE)
> 
> 
> 

-- 
Michal Hocko
SUSE Labs