sched_ext: idle: Respect task affinity in restricted CPU selection

The restricted select_cpu kfunc path handles single-CPU and
migration-disabled tasks without going through scx_select_cpu_dfl().

It currently uses prev_cpu as the candidate, even though prev_cpu is only a
hint and may no longer be usable after an affinity change. With a
caller-provided @allowed mask, this can also return an idle CPU outside
p->cpus_ptr.

Derive the candidate from task state instead: use the sole CPU in
p->cpus_ptr for single-CPU tasks and task_cpu(p) for migration-disabled
tasks. Validate it against p->cpus_ptr and @allowed before claiming its
idle state.

Since the derived candidate may be on a different NUMA node from
prev_cpu, also preserve SCX_PICK_IDLE_IN_NODE by rejecting cross-node
candidates.

Perform all checks before scx_idle_test_and_clear_cpu(), as a successful
call consumes the CPU's idle bit.

Fixes: 683d2d0faba1 ("sched_ext: idle: Introduce scx_bpf_select_cpu_and()")
Cc: stable@vger.kernel.org
Signed-off-by: Hui Su <sh_def@163.com>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

0 files changed, 0 insertions, 0 deletions