Re: Qemu-arm64: LTP: cfs_bandwidth01: Unable to handle kernel NULL pointer dereference at virtual address 0000000000000038

[Cyril Hrubis]

Hi!
> Following kernel crash noticed on Linux stable-rc 6.5.3-rc1 on qemu-arm64 while
> running LTP sched tests cases.
> 
> This is not always reproducible.

What the test does is to create three levels of cgroups, sets CPU
quotas for them, runs bussy loop proceses in the groups and changes the
quotas during the time the bussy processes runs.

And the test is regression test for quite a few commits:

commit 39f23ce07b9355d05a64ae303ce20d1c4b92b957
Author: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Date:   Wed May 13 15:55:28 2020 +0200

    sched/fair: Fix unthrottle_cfs_rq() for leaf_cfs_rq list


commit b34cb07dde7c2346dec73d053ce926aeaa087303
Author: Phil Auld <pauld@xxxxxxxxxx>
Date:   Tue May 12 09:52:22 2020 -0400

    sched/fair: Fix enqueue_task_fair() warning some more

commit fe61468b2cbc2b7ce5f8d3bf32ae5001d4c434e9
Author: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Date:   Fri Mar 6 14:52:57 2020 +0100

    sched/fair: Fix enqueue_task_fair warning

commit 5ab297bab984310267734dfbcc8104566658ebef
Author: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Date:   Fri Mar 6 09:42:08 2020 +0100

    sched/fair: Fix reordering of enqueue/dequeue_task_fair()

commit 6d4d22468dae3d8757af9f8b81b848a76ef4409d
Author: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Date:   Mon Feb 24 09:52:14 2020 +0000

    sched/fair: Reorder enqueue/dequeue_task_fair path

commit fdaba61ef8a268d4136d0a113d153f7a89eb9984
Author: Rik van Riel <riel@xxxxxxxxxxx>
Date:   Mon Jun 21 19:43:30 2021 +0200

    sched/fair: Ensure that the CFS parent is added after unthrottling


Unless this is a random corruption we should look closer at scheduller
changes.

-- 
Cyril Hrubis
chrubis@xxxxxxx