Merge branch 'for-6.12-fixes' into for-6.13

Pull sched_ext/for-6.12-fixes to receive 0e7ffff1b811 ("scx: Fix raciness in
scx_ops_bypass()"). Planned updates for scx_ops_bypass() depends on it.

Signed-off-by: Tejun Heo <tj@kernel.org>

diff --cc kernel/sched/ext.c
index 012a7fc77263037141a361cb3883585b95589dee,3bdb08fc2056aa7341442831b4d7fd0f0055a5dc..c074a64c20f03a173516908d35bc5d6ed831b2a6
--- 1/kernel/sched/ext.c
--- 2/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@@ -3274,70 -3087,21 +3302,65 @@@ static s32 scx_select_cpu_dfl(struct ta
  
        *found = false;
  
-       if (!static_branch_likely(&scx_builtin_idle_enabled)) {
-               scx_ops_error("built-in idle tracking is disabled");
-               return prev_cpu;
-       }
- 
        /*
 -       * If WAKE_SYNC, the waker's local DSQ is empty, and the system is
 -       * under utilized, wake up @p to the local DSQ of the waker. Checking
 -       * only for an empty local DSQ is insufficient as it could give the
 -       * wakee an unfair advantage when the system is oversaturated.
 -       * Checking only for the presence of idle CPUs is also insufficient as
 -       * the local DSQ of the waker could have tasks piled up on it even if
 -       * there is an idle core elsewhere on the system.
 -       */
 -      cpu = smp_processor_id();
 -      if ((wake_flags & SCX_WAKE_SYNC) &&
 -          !cpumask_empty(idle_masks.cpu) && !(current->flags & PF_EXITING) &&
 -          cpu_rq(cpu)->scx.local_dsq.nr == 0) {
 -              if (cpumask_test_cpu(cpu, p->cpus_ptr))
 +       * Determine the scheduling domain only if the task is allowed to run
 +       * on all CPUs.
 +       *
 +       * This is done primarily for efficiency, as it avoids the overhead of
 +       * updating a cpumask every time we need to select an idle CPU (which
 +       * can be costly in large SMP systems), but it also aligns logically:
 +       * if a task's scheduling domain is restricted by user-space (through
 +       * CPU affinity), the task will simply use the flat scheduling domain
 +       * defined by user-space.
 +       */
 +      if (p->nr_cpus_allowed >= num_possible_cpus()) {
 +              if (static_branch_maybe(CONFIG_NUMA, &scx_selcpu_topo_numa))
 +                      numa_cpus = cpumask_of_node(cpu_to_node(prev_cpu));
 +
 +              if (static_branch_maybe(CONFIG_SCHED_MC, &scx_selcpu_topo_llc)) {
 +                      struct sched_domain *sd;
 +
 +                      sd = rcu_dereference(per_cpu(sd_llc, prev_cpu));
 +                      if (sd)
 +                              llc_cpus = sched_domain_span(sd);
 +              }
 +      }
 +
 +      /*
 +       * If WAKE_SYNC, try to migrate the wakee to the waker's CPU.
 +       */
 +      if (wake_flags & SCX_WAKE_SYNC) {
 +              cpu = smp_processor_id();
 +
 +              /*
 +               * If the waker's CPU is cache affine and prev_cpu is idle,
 +               * then avoid a migration.
 +               */
 +              if (cpus_share_cache(cpu, prev_cpu) &&
 +                  test_and_clear_cpu_idle(prev_cpu)) {
 +                      cpu = prev_cpu;
                        goto cpu_found;
 +              }
 +
 +              /*
 +               * If the waker's local DSQ is empty, and the system is under
 +               * utilized, try to wake up @p to the local DSQ of the waker.
 +               *
 +               * Checking only for an empty local DSQ is insufficient as it
 +               * could give the wakee an unfair advantage when the system is
 +               * oversaturated.
 +               *
 +               * Checking only for the presence of idle CPUs is also
 +               * insufficient as the local DSQ of the waker could have tasks
 +               * piled up on it even if there is an idle core elsewhere on
 +               * the system.
 +               */
 +              if (!cpumask_empty(idle_masks.cpu) &&
 +                  !(current->flags & PF_EXITING) &&
 +                  cpu_rq(cpu)->scx.local_dsq.nr == 0) {
 +                      if (cpumask_test_cpu(cpu, p->cpus_ptr))
 +                              goto cpu_found;
 +              }
        }
  
        /*