linux-kernel - Re: [PATCH] generic arch_futex_atomic_op

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Message-ID: <3d9eef14-4059-0f8a-e76f-a8a09d730913@virtuozzo.com>
Date:   Mon, 15 Jul 2019 13:29:45 +0300
From:   Vasily Averin <vvs@...tuozzo.com>
To:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH] generic arch_futex_atomic_op_inuser() cleanup

Looks like this code is dead and therefore looks strange.
I've found it during manual code review and decided to send patch
to pay your attention to this problem.
Probably it's better to remove this code at all?

On 7/15/19 1:27 PM, Vasily Averin wrote:
> Access to 'op' variable does not require pagefault_disable(),
> 'ret' variable should be initialized before using,
> 'oldval' variable can be replaced by constant.
> 
> Signed-off-by: Vasily Averin <vvs@...tuozzo.com>
> ---
>  include/asm-generic/futex.h | 8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/include/asm-generic/futex.h b/include/asm-generic/futex.h
> index 8666fe7f35d7..e9a9655d786d 100644
> --- a/include/asm-generic/futex.h
> +++ b/include/asm-generic/futex.h
> @@ -118,9 +118,7 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
>  static inline int
>  arch_futex_atomic_op_inuser(int op, u32 oparg, int *oval, u32 __user *uaddr)
>  {
> -	int oldval = 0, ret;
> -
> -	pagefault_disable();
> +	int ret = 0;
>  
>  	switch (op) {
>  	case FUTEX_OP_SET:
> @@ -132,10 +130,8 @@ arch_futex_atomic_op_inuser(int op, u32 oparg, int *oval, u32 __user *uaddr)
>  		ret = -ENOSYS;
>  	}
>  
> -	pagefault_enable();
> -
>  	if (!ret)
> -		*oval = oldval;
> +		*oval = 0;
>  
>  	return ret;
>  }
>