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selftests/sched_ext: Handle sleeping task affinity changes in numa test

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When a sleeping task's affinity is changed, task_cpu(p) can be outside
of p->cpus_ptr until after select_task_rq() selects a new runqueue for
the task during wakeup.

Thus, the task's NUMA node determined by numa_select_cpu() can be
completely outside of the task's cpumask, leading to
scx_pick_{idle,any}_cpu_node() failing to find an eligible CPU and
returning -EBUSY. This leads to the numa.bpf.c scheduler abnormally
exiting with the following message in dmesg:

sched_ext: numa: invalid CPU -16
   scx_bpf_cpu_node+0x120/0x190
   bpf_prog_0a34b8e0f515771f_numa_select_cpu+0x108/0x14e
   bpf__sched_ext_ops_select_cpu+0x4f/0xb4
   select_task_rq_scx+0xb0/0x210
   select_task_rq+0xa0/0xd0
   __try_to_wake_up+0x196/0x650
   complete_all+0x76/0x100
   migration_cpu_stop+0x22b/0x300
   cpu_stopper_thread+0xc1/0x180
   smpboot_thread_fn+0x16b/0x230
   kthread+0x2d7/0x350
   ret_from_fork+0x1c2/0x350
   ret_from_fork_asm+0x1a/0x30

Make numa_select_cpu() robust against this case by returning @prev_cpu
if no CPU could be found in the selected NUMA node _and_ we have reason
to believe that the task's affinity was changed while it was sleeping.

Fixes: 5ae5161820 ("selftests/sched_ext: Add NUMA-aware scheduler test")
Signed-off-by: Kuba Piecuch <jpiecuch@google.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Kuba Piecuch 2026-07-23 09:59:55 +00:00 committed by Tejun Heo
parent 9591fcc95d
commit d4a00d61a5
1 changed files with 12 additions and 1 deletions
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13
tools/testing/selftests/sched_ext/numa.bpf.c
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@ -34,7 +34,8 @@ static bool is_cpu_idle(s32 cpu, int node)
s32 BPF_STRUCT_OPS(numa_select_cpu,
struct task_struct *p, s32 prev_cpu, u64 wake_flags)
{
int node = __COMPAT_scx_bpf_cpu_node(scx_bpf_task_cpu(p));
s32 task_cpu = scx_bpf_task_cpu(p);
int node = __COMPAT_scx_bpf_cpu_node(task_cpu);
s32 cpu;
/*
@ -48,6 +49,16 @@ s32 BPF_STRUCT_OPS(numa_select_cpu,
cpu = __COMPAT_scx_bpf_pick_any_cpu_node(p->cpus_ptr, node,
__COMPAT_SCX_PICK_IDLE_IN_NODE);
/*
* @task_cpu may be outside of p->cpus_ptr if @p's affinity
* changed while it was sleeping. This means it's possible for
* p->cpus_ptr to not include any CPUs from @node.
* If we failed to find a cpu in @node, check if @task_cpu
* is outside of p->cpus_ptr and just return @prev_cpu if it is.
*/
if (cpu < 0 && !bpf_cpumask_test_cpu(task_cpu, p->cpus_ptr))
return prev_cpu;
if (is_cpu_idle(cpu, node))
scx_bpf_error("CPU %d should be marked as busy", cpu);