linux-kernel - Re: [PATCH 4/5] x86: wire up TIF_NOTIFY

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Message-ID: <87imbatj3x.fsf@nanos.tec.linutronix.de>
Date:   Fri, 16 Oct 2020 15:07:14 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
        io-uring@...r.kernel.org, peterz@...radead.org
Subject: Re: [PATCH 4/5] x86: wire up TIF_NOTIFY_SIGNAL

On Fri, Oct 16 2020 at 12:54, Oleg Nesterov wrote:
> On 10/16, Thomas Gleixner wrote:
>
> But again, I won't argue. And to remind, we do not really need to touch
> arch_do_signal() at all. We can just add
>
> 	if (test_thread_flag(TIF_NOTIFY_SIGNAL))
> 		tracehook_notify_signal();
>
> 	if (!task_sigpending(current))
> 		return 0;
>
> at the start of get_signal() and avoid the code duplication automatically.

That works as well and is smart, but it's completely non obvious while

     if (ti_work & _TIF_NOTIFY_SIGNAL)
            tracehook_notify_signal();

     arch_do_signal_or_restart(ti_work & _TIF_SIGPENDING);

makes it entirely clear to follow the logic and it just operates on
cached ti_work.

You can still do this for the non generic entry architectures:

     if (!IS_ENABLED(CONFIG_GENERIC_ENTRY) &&
     	 (test_thread_flag(TIF_NOTIFY_SIGNAL))
 		tracehook_notify_signal();

to avoid the churn in arch/*.

Thanks,

        tglx