linux-kernel - Re: [PATCH v2] sched/fair: Fix non-empty throttled_limbo_list warning in tg_throttle

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: <20251028063917.GD33@bytedance>
Date: Tue, 28 Oct 2025 14:39:18 +0800
From: Aaron Lu <ziqianlu@...edance.com>
To: K Prateek Nayak <kprateek.nayak@....com>
Cc: Hao Jia <jiahao.kernel@...il.com>, mingo@...hat.com,
	peterz@...radead.org, mingo@...nel.org, juri.lelli@...hat.com,
	vincent.guittot@...aro.org, dietmar.eggemann@....com,
	rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
	vschneid@...hat.com, linux-kernel@...r.kernel.org,
	Hao Jia <jiahao1@...iang.com>
Subject: Re: [PATCH v2] sched/fair: Fix non-empty throttled_limbo_list
 warning in tg_throttle_down()

On Tue, Oct 28, 2025 at 08:33:15AM +0530, K Prateek Nayak wrote:
> Hello Aaron,
> 
> On 10/27/2025 5:32 PM, Aaron Lu wrote:
> > On Mon, Oct 27, 2025 at 05:05:34PM +0800, Hao Jia wrote:
> >> @@ -6403,7 +6407,7 @@ static void do_sched_cfs_slack_timer(struct cfs_bandwidth *cfs_b)
> >>   * expired/exceeded, otherwise it may be allowed to steal additional ticks of
> >>   * runtime as update_curr() throttling can not trigger until it's on-rq.
> >>   */
> >> -static void check_enqueue_throttle(struct cfs_rq *cfs_rq)
> >> +static void check_enqueue_throttle(struct cfs_rq *cfs_rq, int flags)
> >>  {
> >>  	if (!cfs_bandwidth_used())
> >>  		return;
> >> @@ -6418,6 +6422,13 @@ static void check_enqueue_throttle(struct cfs_rq *cfs_rq)
> >>  
> >>  	/* update runtime allocation */
> >>  	account_cfs_rq_runtime(cfs_rq, 0);
> >> +	/*
> >> +	 * Do not attempt to throttle on the cfs_rq unthrottle path.
> >> +	 * and it must be placed after account_cfs_rq_runtime() to
> >> +	 * prevent a possible missed start of the bandwidth timer.
> > 
> > Hi Prateek and Hao,
> > 
> > Does it matter to start the bw timer? If no cfs_rq gets throttled, the
> > timer doesn't look that useful.
> 
> Ack! But if we've reached here with ENQUEUE_THROTTLE set, we are in fact
> trying to enqueue a task during unthrottling and we only start the timer
> if we don't have any bandwidth since __account_cfs_rq_runtime() would bail
> out if "cfs_rq->runtime_remaining > 0"
> > Also, account_cfs_rq_runtime() calls
> > assign_cfs_rq_runtime() and if assign failed, it will do resched_curr()
> > but since we do not throttle cfs_rq here, that resched would be useless.
> 
> resched only happens if "cfs_rq->curr" is set andcheck_enqueue_throttle() already bails out if "cfs_rq->curr" is set so
> the resched is avoided.

Right, sorry I missed that.