From e9fe182772dcb2630964724fd93e9c90b68ea0fd Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Fri, 24 Jan 2025 10:48:25 -1000 Subject: [PATCH] sched_ext: selftests/dsp_local_on: Fix sporadic failures 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 Reported-by: Ihor Solodrai Cc: Andrea Righi Cc: Changwoo Min --- tools/testing/selftests/sched_ext/dsp_local_on.bpf.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/tools/testing/selftests/sched_ext/dsp_local_on.bpf.c b/tools/testing/selftests/sched_ext/dsp_local_on.bpf.c index fbda6bf54671..758b479bd1ee 100644 --- a/tools/testing/selftests/sched_ext/dsp_local_on.bpf.c +++ b/tools/testing/selftests/sched_ext/dsp_local_on.bpf.c @@ -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);