linux-kernel - Re: [PATCH] sched/fair: Add null pointer check to pick_next

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Message-ID: <0049c6a0-8802-416c-9618-9d714c22af49@meta.com>
Date: Mon, 14 Apr 2025 11:38:15 -0400
From: Chris Mason <clm@...a.com>
To: Peter Zijlstra <peterz@...radead.org>, Rik van Riel <riel@...riel.com>
Cc: Pat Cody <pat@...cody.io>, mingo@...hat.com, 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, patcody@...a.com,
        kernel-team@...a.com, stable@...r.kernel.org,
        Breno Leitao <leitao@...ian.org>
Subject: Re: [PATCH] sched/fair: Add null pointer check to pick_next_entity()



On 4/14/25 5:08 AM, Peter Zijlstra wrote:

[ math and such ]


> The zero_vruntime patch I gave earlier should avoid this particular
> issue.

Here's a crash with the zero runtime patch.  I'm trying to reproduce
this outside of prod so we can crank up the iteration speed a bit.

-chris

nr_running = 2
zero_vruntime = 19194347104893960
avg_vruntime = 6044054790
avg_load = 2
curr = {
  cgroup urgent
  vruntime = 24498183812106172
  weight = 3561684 => 3478
  rq = {
    nr_running = 0
    zero_vruntime = 505000008215941
    avg_vruntime = 0
    avg_load = 0
    curr = {
      cgroup urgent/-610604968056586240
      vruntime = 505000008302509
      weight = 455902 => 445
      rq = {
        nr_running = 0
        zero_vruntime = 12234709899
        avg_vruntime = 0
        avg_load = 0
        curr = {
          task = 279047 (fc0)
          vruntime = 12237278090
          weight = 15360 => 15
        }
        tasks_timeline = [
        ]
      }
    }
    tasks_timeline = [
    ]
  }
}
tasks_timeline = [
  {
    cgroup optional
    vruntime = 19194350126921355
    weight = 1168 => 2
    rq = {
      nr_running = 2
      zero_vruntime = 440280059357029
      avg_vruntime = 476
      avg_load = 688
      tasks_timeline = [
        {
          cgroup optional/-610613050111295488
          vruntime = 440280059333960
          weight = 291271 => 284
          rq = {
            nr_running = 5
            zero_vruntime = 65179829005
            avg_vruntime = 0
            avg_load = 75
            tasks_timeline = [
              {
                task = 261672 (fc0)
                vruntime = 65189926507
                weight = 15360 => 15
              },
              {
                task = 261332 (fc0)
                vruntime = 65189480962
                weight = 15360 => 15
              },
              {
                task = 261329 (enc1:0:vp9_fbv)
                vruntime = 65165843516
                weight = 15360 => 15
              },
              {
                task = 261334 (dec0:0:hevc_fbv)
                vruntime = 65174065035
                weight = 15360 => 15
              },
              {
                task = 261868 (fc0)
                vruntime = 65179829005
                weight = 15360 => 15
              },
            ]
          }
        },
        {
          cgroup optional/-610609318858457088
          vruntime = 440280059373247
          weight = 413911 => 404
          rq = {
            nr_running = 1
            zero_vruntime = 22819875784
            avg_vruntime = 0
            avg_load = 15
            tasks_timeline = [
              {
                task = 273291 (fc0)
                vruntime = 22819875784
                weight = 15360 => 15
              },
            ]
          }
        },
      ]
    }
  },
]