linux-kernel - Re: [PATCH 12/24] sched/fair: Prepare exit/cleanup paths for delayed

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <xhsmh8qx0y4n0.mognet@vschneid-thinkpadt14sgen2i.remote.csb>
Date: Tue, 13 Aug 2024 14:43:47 +0200
From: Valentin Schneider <vschneid@...hat.com>
To: Peter Zijlstra <peterz@...radead.org>, mingo@...hat.com,
 peterz@...radead.org, juri.lelli@...hat.com, vincent.guittot@...aro.org,
 dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
 mgorman@...e.de, linux-kernel@...r.kernel.org
Cc: kprateek.nayak@....com, wuyun.abel@...edance.com,
 youssefesmat@...omium.org, tglx@...utronix.de, efault@....de
Subject: Re: [PATCH 12/24] sched/fair: Prepare exit/cleanup paths for
 delayed_dequeue

On 27/07/24 12:27, Peter Zijlstra wrote:
> @@ -12817,10 +12830,26 @@ static void attach_task_cfs_rq(struct ta
>  static void switched_from_fair(struct rq *rq, struct task_struct *p)
>  {
>       detach_task_cfs_rq(p);
> +	/*
> +	 * Since this is called after changing class, this isn't quite right.
> +	 * Specifically, this causes the task to get queued in the target class
> +	 * and experience a 'spurious' wakeup.
> +	 *
> +	 * However, since 'spurious' wakeups are harmless, this shouldn't be a
> +	 * problem.
> +	 */
> +	p->se.sched_delayed = 0;
> +	/*
> +	 * While here, also clear the vlag, it makes little sense to carry that
> +	 * over the excursion into the new class.
> +	 */
> +	p->se.vlag = 0;

RQ lock is held, the task can't be current if it's ->sched_delayed; is a
dequeue_task() not possible at this point?  Or just not worth it?