From: Tejun Heo <tj@kernel.org> mainline inclusion from mainline-v6.12-rc1 commit e7a6395a889a82edb1cdcebc2c66646aca454658 category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/IDC9YK Reference: https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commi... -------------------------------- When a running task is migrated to another CPU, the stop_task is used to preempt the running task and migrate it. This, expectedly, invokes ops.cpu_release(). If the BPF scheduler then calls scx_bpf_reenqueue_local(), it re-enqueues all tasks on the local DSQ including the task which is being migrated. This creates an unnecessary re-enqueue of a task which is about to be deactivated and re-activated for migration anyway. It can also cause confusion for the BPF scheduler as scx_bpf_task_cpu() of the task and its allowed CPUs may not agree while migration is pending. Signed-off-by: Tejun Heo <tj@kernel.org> Fixes: 245254f7081d ("sched_ext: Implement sched_ext_ops.cpu_acquire/release()") Acked-by: David Vernet <void@manifault.com> Signed-off-by: Zicheng Qu <quzicheng@huawei.com> --- kernel/sched/ext.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index f5f58bc7d364..c71aae5a3f3f 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -5650,6 +5650,20 @@ __bpf_kfunc u32 scx_bpf_reenqueue_local(void) */ list_for_each_entry_safe(p, n, &rq->scx.local_dsq.list, scx.dsq_list.node) { + /* + * If @p is being migrated, @p's current CPU may not agree with + * its allowed CPUs and the migration_cpu_stop is about to + * deactivate and re-activate @p anyway. Skip re-enqueueing. + * + * While racing sched property changes may also dequeue and + * re-enqueue a migrating task while its current CPU and allowed + * CPUs disagree, they use %ENQUEUE_RESTORE which is bypassed to + * the current local DSQ for running tasks and thus are not + * visible to the BPF scheduler. + */ + if (p->migration_pending) + continue; + dispatch_dequeue(rq, p); list_add_tail(&p->scx.dsq_list.node, &tasks); } -- 2.34.1