Commit 06efc9fe authored by Andrea Righi's avatar Andrea Righi Committed by Tejun Heo
Browse files

sched_ext: idle: Handle migration-disabled tasks in idle selection 



When SCX_OPS_ENQ_MIGRATION_DISABLED is enabled, migration-disabled tasks
are also routed to ops.enqueue(). A scheduler may attempt to dispatch
such tasks directly to an idle CPU using the default idle selection
policy via scx_bpf_select_cpu_and() or scx_bpf_select_cpu_dfl().

This scenario must be properly handled by the built-in idle policy to
avoid returning an idle CPU where the target task isn't allowed to run.
Otherwise, it can lead to errors such as:

 EXIT: runtime error (SCX_DSQ_LOCAL[_ON] cannot move migration disabled Chrome_ChildIOT[291646] from CPU 3 to 14)

Prevent this by explicitly handling migration-disabled tasks in the
built-in idle selection logic, maintaining their CPU affinity.

Fixes: a730e3f7 ("sched_ext: idle: Consolidate default idle CPU selection kfuncs")
Signed-off-by: default avatarAndrea Righi <arighi@nvidia.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent e14fd98c

kernel/sched/ext_idle.c

+1 −1
Original line number Diff line number Diff line
@@ -903,7 +903,7 @@ s32 select_cpu_from_kfunc(struct task_struct *p, s32 prev_cpu, u64 wake_flags, 
	 * selection optimizations and simply check whether the previously

	 * used CPU is idle and within the allowed cpumask.

	 */

	if (p->nr_cpus_allowed == 1) {

	if (p->nr_cpus_allowed == 1 || is_migration_disabled(p)) {

		if (cpumask_test_cpu(prev_cpu, allowed ?: p->cpus_ptr) &&

		    scx_idle_test_and_clear_cpu(prev_cpu))

			cpu = prev_cpu;