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sched_ext: selftests/dsp_local_on: Fix sporadic failures

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dsp_local_on has several incorrect assumptions, one of which is that
p->nr_cpus_allowed always tracks p->cpus_ptr. This is not true when a task
is scheduled out while migration is disabled - p->cpus_ptr is temporarily
overridden to the previous CPU while p->nr_cpus_allowed remains unchanged.

This led to sporadic test faliures when dsp_local_on_dispatch() tries to put
a migration disabled task to a different CPU. Fix it by keeping the previous
CPU when migration is disabled.

There are SCX schedulers that make use of p->nr_cpus_allowed. They should
also implement explicit handling for p->migration_disabled.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Ihor Solodrai <ihor.solodrai@pm.me>
Cc: Andrea Righi <arighi@nvidia.com>
Cc: Changwoo Min <changwoo@igalia.com>
This commit is contained in:
Tejun Heo 2025-01-24 10:48:25 -10:00
parent 74ca334338
commit e9fe182772
1 changed files with 1 additions and 1 deletions
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2
tools/testing/selftests/sched_ext/dsp_local_on.bpf.c
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@ -43,7 +43,7 @@ void BPF_STRUCT_OPS(dsp_local_on_dispatch, s32 cpu, struct task_struct *prev)
if (!p)
return;
if (p->nr_cpus_allowed == nr_cpus)
if (p->nr_cpus_allowed == nr_cpus && !p->migration_disabled)
target = bpf_get_prandom_u32() % nr_cpus;
else
target = scx_bpf_task_cpu(p);