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Date:   Thu, 15 Oct 2020 17:17:56 +0200
From:   Oleg Nesterov <oleg@redhat.com>
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     Jens Axboe <axboe@kernel.dk>, linux-kernel@vger.kernel.org,
        io-uring@vger.kernel.org, peterz@infradead.org
Subject: Re: [PATCH 4/5] x86: wire up TIF_NOTIFY_SIGNAL
Message-ID: <20201015151756.GK24156@redhat.com>
References: <20201015143409.GC24156@redhat.com>
 <87v9fbv8te.fsf@nanos.tec.linutronix.de>
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On 10/15, Thomas Gleixner wrote:
>
> On Thu, Oct 15 2020 at 16:34, Oleg Nesterov wrote:
> > On 10/15, Thomas Gleixner wrote:
> >> Instead of adding this to every architectures signal magic, we can
> >> handle TIF_NOTIFY_SIGNAL in the core code:
> >>
> >> static void handle_singal_work(ti_work, regs)
> >> {
> >> 	if (ti_work & _TIF_NOTIFY_SIGNAL)
> >>         	tracehook_notify_signal();
> >>
> >>         arch_do_signal(ti_work, regs);
> >> }
> >>
> >>       loop {
> >>       		if (ti_work & (SIGPENDING | NOTIFY_SIGNAL))
> >>                 	handle_signal_work(ti_work, regs);
> >>       }
> >
> > To me this looks like unnecessary complication. We need to change
> > every architecture anyway, how can this helper help?
>
> You need to change ONE architecture because nobody else uses the common
> entry loop right now.

so we need to change other arches to use the common entry loop.

> For those who move over they have to supply
> arch_do_signal() anyway,

and this arch_do_signal() should be changed to check _TIF_SIGPENDING.


See also my replies to 3/5. I strongly disagree with CONFIG_GENERIC_ENTRY.
But even if we require CONFIG_GENERIC_ENTRY, why do we want this helper?

We can just change exit_to_user_mode_loop() to do

	if (ti_work & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL)) {
		if (ti_work & _TIF_NOTIFY_SIGNAL)
			tracehook_notify_signal();
		arch_do_signal(ti_work, regs);
	}

but I'd prefer to handle SIGPENDING/NOTIFY_SIGNAL in one place.

Oleg.