linux-kernel - Re: [PATCH v0.9.1 3/6] sched/umcg: implement UMCG syscalls

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Message-ID: <YaFY0KqfPhmZjK7n@hirez.programming.kicks-ass.net>
Date:   Fri, 26 Nov 2021 22:59:44 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Peter Oskolkov <posk@...k.io>, Ingo Molnar <mingo@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-api@...r.kernel.org, Paul Turner <pjt@...gle.com>,
        Ben Segall <bsegall@...gle.com>,
        Peter Oskolkov <posk@...gle.com>,
        Andrei Vagin <avagin@...gle.com>, Jann Horn <jannh@...gle.com>,
        Thierry Delisle <tdelisle@...terloo.ca>
Subject: Re: [PATCH v0.9.1 3/6] sched/umcg: implement UMCG syscalls

On Fri, Nov 26, 2021 at 10:08:14PM +0100, Thomas Gleixner wrote:
> On Fri, Nov 26 2021 at 18:09, Peter Zijlstra wrote:
> > +
> > +	if (timo) {
> > +		hrtimer_init_sleeper_on_stack(&timeout, tsk->umcg_clock,
> > +					      HRTIMER_MODE_ABS);
> > +		hrtimer_set_expires_range_ns(&timeout.timer, (s64)timo,
> > +					     tsk->timer_slack_ns);
> > +	}
> > +
> > +	for (;;) {
> > +		set_current_state(TASK_INTERRUPTIBLE);
> > +
> > +		ret = -EINTR;
> > +		if (signal_pending(current))
> > +			break;
> > +
> > +		/*
> > +		 * Faults can block and scribble our wait state.
> > +		 */
> > +		pagefault_disable();
> > +		if (get_user(state, &self->state)) {
> > +			pagefault_enable();
> > +
> > +			ret = -EFAULT;
> > +			if (page) {
> > +				unpin_user_page(page);
> > +				page = NULL;
> > +				break;
> > +			}
> > +
> > +			if (pin_user_pages_fast((unsigned long)self, 1, 0, &page) != 1) {
> > +				page = NULL;
> > +				break;
> > +			}
> > +
> > +			continue;
> > +		}
> > +
> > +		if (page) {
> > +			unpin_user_page(page);
> > +			page = NULL;
> > +		}
> > +		pagefault_enable();
> > +
> > +		state &= UMCG_TASK_MASK;
> > +		if (state != UMCG_TASK_RUNNABLE) {
> > +			ret = 0;
> > +			if (state == UMCG_TASK_RUNNING)
> > +				break;
> > +
> > +			ret = -EINVAL;
> > +			break;
> > +		}
> > +
> > +		if (timo)
> > +			hrtimer_sleeper_start_expires(&timeout, HRTIMER_MODE_ABS);
> > +
> > +		freezable_schedule();
> 
> You can replace the whole hrtimer foo with
> 
>                 if (!schedule_hrtimeout_range_clock(timo ? &timo : NULL,
>                                                     tsk->timer_slack_ns,
>                                                     HRTIMER_MODE_ABS,
>                                                     tsk->umcg_clock)) {
>                 	ret = -ETIMEOUT;
>                         break;
>                 }

That seems to loose the freezable crud.. then again, since we're
interruptible, that shouldn't matter. Lemme go do that.