Re: [PATCH 0/4] sched: Various reweight_entity() fixes

[Dietmar Eggemann <dietmar.eggemann@arm.com>]

On 16.02.26 04:14, K Prateek Nayak wrote:
> Hello Shubhang,
> 
> On 2/14/2026 12:50 PM, Shubhang Kaushik wrote:
>> Hi Peter,
>>
>> On Fri, 30 Jan 2026, Peter Zijlstra wrote:
>>
>>> Two issues related to reweight_entity() were raised; poking at all that got me
>>> these patches.
>>>
>>> They're in queue.git/sched/core and I spend most of yesterday staring at traces
>>> trying to find anything wrong. So far, so good.
>>>
>>> Please test.
>>>
>>>
>>
>> I’m seeing a consistent NULL pointer dereference in pick_task_fair() when running hackbench on an Ampere Altra (80 cores arm64). This is happening after applying the complete patchset on the latest 6.19.0+ kernel with PREEMPT_DYNAMIC (full), CONFIG_SCHED_CLUSTER and NOHZ_FULL enabled.
> 
> Can you confirm you using the latest changes from:
> 
>   git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git sched/core
> 
> at commit bdba3187771c ("sched/fair: Use full weight to __calc_delta()")
> since this series has undergone some churn throughout the week?

I saw the same issue on my Arm64 big.Little board (12 CPUs) with the old
'queue.git sched/core' (i.e before s/div_s64()/div64_long()) in:

sched/fair: Increase weight bits for avg_vruntime

and test:

for ((i=0; i<20000; i++)) do yes > /dev/null & done

It's gone with:

  git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git sched/core

  commit bdba3187771c ("sched/fair: Use full weight to __calc_delta()")

Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>

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