Commit da2d81b4 authored by Tejun Heo's avatar Tejun Heo
Browse files

sched_ext: Skip tasks with stale task_rq in bypass_lb_cpu() 



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: 95d1df61 ("sched_ext: Implement load balancer for bypass mode")
Cc: stable@vger.kernel.org # v6.19+
Reported-by: default avatarChris Mason <clm@meta.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Reviewed-by: default avatarAndrea Righi <arighi@nvidia.com>
parent 4fda9f0e

kernel/sched/ext.c

+9 −0
Original line number Diff line number Diff line
@@ -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;