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

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Date:   Thu, 1 Aug 2019 17:39:36 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>
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 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...

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() ?

Oleg.