linux-kernel - Re: [patch 4/5] posix-cpu-timers: Defer timer handling to task

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Message-ID: <alpine.DEB.2.21.1908012035130.1789@nanos.tec.linutronix.de>
Date:   Thu, 1 Aug 2019 20:41:22 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Oleg Nesterov <oleg@...hat.com>
cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Sebastian Siewior <bigeasy@...utronix.de>,
        Anna-Maria Gleixner <anna-maria@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Julia Cartwright <julia@...com>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Frederic Weisbecker <fweisbec@...il.com>,
        John Stultz <john.stultz@...aro.org>,
        Andy Lutomirski <luto@...nel.org>,
        "Paul E. McKenney" <paulmck@...ux.ibm.com>, kvm@...r.kernel.org,
        Radim Krcmar <rkrcmar@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [patch 4/5] posix-cpu-timers: Defer timer handling to
 task_work

On Thu, 1 Aug 2019, Oleg Nesterov wrote:
> On 08/01, Thomas Gleixner wrote:
> >
> > +static void __run_posix_cpu_timers(struct task_struct *tsk)
> > +{
> > +	/* FIXME: Init it proper in fork or such */
> > +	init_task_work(&tsk->cpu_timer_work, posix_cpu_timers_work);
> > +	task_work_add(tsk, &tsk->cpu_timer_work, true);
> > +}
> 
> What if update_process_times/run_posix_cpu_timers is called again before
> this task does task_work_run() ?
> 
> somehow it should check that ->cpu_timer_work is not already queued...

Right.

> Or suppose that this is called when task_work_run() executes this
> cpu_timer_work. Looks like you need another flag checked by
> __run_posix_cpu_timers() and cleare in posix_cpu_timers_work() ?

That's a non issue. The only thing which can happen is that it runs through
the task_work once more to figure out there is nothing to do.

Thanks,

	tglx