linux-kernel - Re: [PATCH 0/4] sched: Various reweight

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: <d3e16de8-cf41-40b0-a976-fb2f37608b70@amd.com>
Date: Wed, 11 Feb 2026 14:20:31 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: Peter Zijlstra <peterz@...radead.org>
CC: Doug Smythies <dsmythies@...us.net>, <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>,
	<wangtao554@...wei.com>, <quzicheng@...wei.com>, <wuyun.abel@...edance.com>
Subject: Re: [PATCH 0/4] sched: Various reweight_entity() fixes

Hello Peter,

On 2/11/2026 11:58 AM, K Prateek Nayak wrote:
> I'll go back and fix my debug patch to give a full view of series of
> events that leads to this but in the meantime I've added the full log
> below if someone wants to take a look.

Attached is archive of trace. Should expand to give a "timeline.trace"
file. Following are some series of events before the failed pick:


  Note: "cfs_rq: depth(1) ..." is the cfs_rq which fails but the first
  "dump_h_overflow_cfs_rq: cfs_rq: ..." will note depth as "0" which is
  the depth of padding and is not the actual cfs-rq depth.

  The lines after "pick_task_fair: cfs_rq of overflow:" dumps the cfs_rq
  and the queued entities that failed the pick.

  ...
  [006] ... : __enqueue_entity: Enqueue cfs_rq: depth(1) weight(2169503744) nr_queued(2069) sum_w_vruntime(-7389160032126894080) sum_weight(2169503744) zero_vruntime(18446744052406571137) sum_shift(0) avg_vruntime(18446744052406571137)
  [006] ... : __dequeue_entity: Dequeue cfs_rq: depth(1) weight(2169503744) nr_queued(2069) sum_w_vruntime(3512818056739946496) sum_weight(2168455168) zero_vruntime(18446744055883646744) sum_shift(0) avg_vruntime(18446744055883646744)
  [006] ... : __enqueue_entity: Enqueue cfs_rq: depth(1) weight(2169503744) nr_queued(2069) sum_w_vruntime(1653261820069150720) sum_weight(2169503744) zero_vruntime(18446744056741357296) sum_shift(0) avg_vruntime(18446744056741357296)
  [006] ... : __dequeue_entity: Dequeue cfs_rq: depth(1) weight(2169503744) nr_queued(2069) sum_w_vruntime(3337798565006147584) sum_weight(2168455168) zero_vruntime(18446744055964215508) sum_shift(0) avg_vruntime(18446744055964215508)
  ...
  [006] ... : __enqueue_entity: Enqueue cfs_rq: depth(1) weight(2169503744) nr_queued(2069) sum_w_vruntime(-4817868778594369536) sum_weight(2169503744) zero_vruntime(18446744051221380982) sum_shift(0) avg_vruntime(18446744051221380982)
  [006] ... : __dequeue_entity: Dequeue cfs_rq: depth(1) weight(2169503744) nr_queued(2069) sum_w_vruntime(8703580922935508992) sum_weight(2168455168) zero_vruntime(18446744053489887930) sum_shift(0) avg_vruntime(18446744053489887930)
  ...
  [006] ... : __enqueue_entity: Enqueue cfs_rq: depth(1) weight(2169503744) nr_queued(2069) sum_w_vruntime(1049195167414747136) sum_weight(2169503744) zero_vruntime(18446744057019812035) sum_shift(0) avg_vruntime(18446744057019812035)
  [006] ... : __dequeue_entity: Dequeue cfs_rq: depth(1) weight(2169503744) nr_queued(2069) sum_w_vruntime(2118331978874880000) sum_weight(2168455168) zero_vruntime(18446744056526599437) sum_shift(0) avg_vruntime(18446744056526599437)
  ...
  [006] ... : __enqueue_entity: Enqueue cfs_rq: depth(1) weight(2169503744) nr_queued(2069) sum_w_vruntime(8649466989629145088) sum_weight(2169503744) zero_vruntime(18446744053516583405) sum_shift(0) avg_vruntime(18446744053516583405)
  [006] ... : __dequeue_entity: Dequeue cfs_rq: depth(1) weight(2169503744) nr_queued(2069) sum_w_vruntime(-984823152929406976) sum_weight(2168455168) zero_vruntime(18446744049450913118) sum_shift(0) avg_vruntime(18446744049450913118)

  ...

  [006] ... : pick_task_fair: cfs_rq of overflow: /* Essentially failed pick. */
  [006] ... : dump_h_overflow_cfs_rq: cfs_rq: ... weight(2169503744) nr_queued(2069) sum_w_vruntime(-59587237455593472) sum_weight(2168455168) zero_vruntime(18446744049024233365) sum_shift(0) avg_vruntime(18446744049024233365)
  [006] ... : dump_h_overflow_entity: se: weight(1048576) vruntime(18446744057295755695) slice(2800000) deadline(18446744057298552230) curr?(1) task?(1) delayed?(0) se_depth(1)
  [006] ... : dump_h_overflow_entity: se: weight(1048576) vruntime(18446744057379145967) slice(2800000) deadline(18446744057381940989) curr?(0) task?(1) delayed?(0) se_depth(1)
  [006] ... : dump_h_overflow_entity: se: weight(1048576) vruntime(18446744057463106601) slice(2800000) deadline(18446744057465901974) curr?(0) task?(1) delayed?(0) se_depth(1)
  [006] ... : dump_h_overflow_entity: se: weight(1048576) vruntime(18446744057487667304) slice(2800000) deadline(18446744057490461976) curr?(0) task?(1) delayed?(0) se_depth(1)
  [006] ... : dump_h_overflow_entity: se: weight(1048576) vruntime(18446744058420769904) slice(2800000) deadline(18446744058423566108) curr?(0) task?(1) delayed?(0) se_depth(1)
  [006] ... : dump_h_overflow_entity: se: weight(1048576) vruntime(18446744058486927372) slice(2800000) deadline(18446744058489723636) curr?(0) task?(1) delayed?(0) se_depth(1)
  [006] ... : dump_h_overflow_entity: se: weight(1048576) vruntime(18446744061273836896) slice(2800000) deadline(18446744061276631077) curr?(0) task?(1) delayed?(0) se_depth(1)
  [006] ... : dump_h_overflow_entity: se: weight(1048576) vruntime(18446744061535759861) slice(2800000) deadline(18446744061538554473) curr?(0) task?(1) delayed?(0) se_depth(1)
  [006] ... : dump_h_overflow_entity: se: weight(1048576) vruntime(18446744061788668421) slice(2800000) deadline(18446744061791464976) curr?(0) task?(1) delayed?(0) se_depth(1)
  [006] ... : dump_h_overflow_entity: se: weight(1048576) vruntime(18446744062846656914) slice(2800000) deadline(18446744062849454680) curr?(0) task?(1) delayed?(0) se_depth(1)
  [006] ... : dump_h_overflow_entity: se: weight(1048576) vruntime(18446744064164417134) slice(2800000) deadline(18446744064167214230) curr?(0) task?(1) delayed?(0) se_depth(1)
  [006] ... : dump_h_overflow_entity: se: weight(1048576) vruntime(18446744065239426914) slice(2800000) deadline(18446744065242224540) curr?(0) task?(1) delayed?(0) se_depth(1)
  [006] ... : dump_h_overflow_entity: se: weight(1048576) vruntime(880604900) slice(2800000) deadline(883328346) curr?(0) task?(1) delayed?(0) se_depth(1)
  [006] ... : dump_h_overflow_entity: se: weight(1048576) vruntime(880537321) slice(2800000) deadline(883331492) curr?(0) task?(1) delayed?(0) se_depth(1)
  [006] ... : dump_h_overflow_entity: se: weight(1048576) vruntime(880537194) slice(2800000) deadline(883333328) curr?(0) task?(1) delayed?(0) se_depth(1)
  [006] ... : dump_h_overflow_entity: se: weight(1048576) vruntime(880540318) slice(2800000) deadline(883334689) curr?(0) task?(1) delayed?(0) se_depth(1)
  ...


The avg_vruntime(18446744049024233365) = -24685318251 (s64) is smaller
than that of all the vruntime of queued entities.

Peter, Could it be the "left bias" in avg_vruntime() coming into play
with larger "cfs_rq->sum_weight"?

-- 
Thanks and Regards,
Prateek

Download attachment "timeline.tar.gz" of type "application/x-gzip" (1200020 bytes)