linux-kernel - Re: [PATCH 2/2] kernel/signal.c: explicitly initialize si

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Date: Thu, 22 Feb 2024 20:05:47 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: wenyang.linux@...mail.com
Cc: Christian Brauner <brauner@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Luis Chamberlain <mcgrof@...nel.org>,
	Mike Christie <michael.christie@...cle.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Vincent Whitchurch <vincent.whitchurch@...s.com>,
	Ard Biesheuvel <ardb@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] kernel/signal.c: explicitly initialize si_code and
 use ksig->info uniformly

On 02/23, wenyang.linux@...mail.com wrote:
>
> From: Wen Yang <wenyang.linux@...mail.com>
>
> By explicitly initializing ksig->info.si_code and uniformly using ksig->info,
> get_signal() function could be slightly optimized, as folowes:

I don't understand. Why do you think it will be optimized? in what sense?

> 	clear_siginfo(&ksig->info);
> 	ksig->info.si_signo = signr = SIGKILL;          --> missed si_code

because we do not need to set .si_code in this case?

> 	sigdelset(&current->pending.signal, SIGKILL);
> 	trace_signal_deliver(SIGKILL, SEND_SIG_NOINFO,  --> unnecessary SEND_SIG_NOINFO

Why do you think the usage of SEND_SIG_NOINFO is "unnecessary" or bad?
To me this looks good.

> @@ -2732,8 +2732,9 @@ bool get_signal(struct ksignal *ksig)
>  		     signal->group_exec_task) {
>  			clear_siginfo(&ksig->info);
>  			ksig->info.si_signo = signr = SIGKILL;
> +			ksig->info.si_code = SI_USER;
>  			sigdelset(&current->pending.signal, SIGKILL);
> -			trace_signal_deliver(SIGKILL, SEND_SIG_NOINFO,
> +			trace_signal_deliver(SIGKILL, &ksig->info,

Well. to me this look like the minor but unnecessary pessimization.

AFAICS, we do not need to initialize .si_code. The usage if ksig->info
instead of ksig->info means that TP_STORE_SIGINFO() will actually read
the memory.

Sorry, I don't understand the point at all :/

and it seems that we can simply kill clear_siginfo(), but this is
another story.

Oleg.