linux-kernel - Re: [PATCH v1 05/20] signal: flatten do_send_sig

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Date:   Tue, 29 May 2018 07:28:27 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Christian Brauner <christian@...uner.io>
Cc:     linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org,
        mingo@...nel.org, james.morris@...rosoft.com,
        keescook@...omium.org, peterz@...radead.org, sds@...ho.nsa.gov,
        viro@...iv.linux.org.uk, akpm@...ux-foundation.org, oleg@...hat.com
Subject: Re: [PATCH v1 05/20] signal: flatten do_send_sig_info()

Christian Brauner <christian@...uner.io> writes:

> Let's return early when lock_task_sighand() fails and move send_signal()
> and unlock_task_sighand() out of the if block.

Introducing multiple exits into a function.  Ick.
You do know that is what Dijkstra was arguing against in his paper
"Goto Considered Harmful"

That introduces mutiple exits and makes the function harder to analyze.
It is especially a pain as I have something in my queue that will
shuffle things around and remove the possibility of lock_task_sighand
failing.

Eric

> Signed-off-by: Christian Brauner <christian@...uner.io>
> ---
> v0->v1:
> * patch unchanged
> ---
>  kernel/signal.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/signal.c b/kernel/signal.c
> index baae137455eb..a628b56415e6 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -1167,16 +1167,16 @@ specific_send_sig_info(int sig, struct siginfo *info, struct task_struct *t)
>  }
>  
>  int do_send_sig_info(int sig, struct siginfo *info, struct task_struct *p,
> -			bool group)
> +		     bool group)
>  {
>  	unsigned long flags;
>  	int ret = -ESRCH;
>  
> -	if (lock_task_sighand(p, &flags)) {
> -		ret = send_signal(sig, info, p, group);
> -		unlock_task_sighand(p, &flags);
> -	}
> +	if (!lock_task_sighand(p, &flags))
> +		return ret;
>  
> +	ret = send_signal(sig, info, p, group);
> +	unlock_task_sighand(p, &flags);
>  	return ret;
>  }