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Message-ID: <20240222190546.GA5993@redhat.com>
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(¤t->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(¤t->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.
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