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sched_ext: Skip tasks with stale task_rq in bypass_lb_cpu()

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bypass_lb_cpu() transfers tasks between per-CPU bypass DSQs without
migrating them - task_cpu() only updates when the donee later consumes the
task via move_remote_task_to_local_dsq(). If the LB timer fires again before
consumption and the new DSQ becomes a donor, @p is still on the previous CPU
and task_rq(@p) != donor_rq. @p can't be moved without its own rq locked.

Skip such tasks.

Fixes: 95d1df610c ("sched_ext: Implement load balancer for bypass mode")
Cc: stable@vger.kernel.org # v6.19+
Reported-by: Chris Mason <clm@meta.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
This commit is contained in:
Tejun Heo 2026-04-24 14:31:35 -10:00
parent 4fda9f0e7c
commit da2d81b411
1 changed files with 9 additions and 0 deletions
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9
kernel/sched/ext.c
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@ -5023,6 +5023,15 @@ static u32 bypass_lb_cpu(struct scx_sched *sch, s32 donor,
if (cpumask_empty(donee_mask))
break;
/*
* If an earlier pass placed @p on @donor_dsq from a different
* CPU and the donee hasn't consumed it yet, @p is still on the
* previous CPU and task_rq(@p) != @donor_rq. @p can't be moved
* without its rq locked. Skip.
*/
if (task_rq(p) != donor_rq)
continue;
donee = cpumask_any_and_distribute(donee_mask, p->cpus_ptr);
if (donee >= nr_cpu_ids)
continue;