From 1dd6c84f1c544e552848a8968599220bd464e338 Mon Sep 17 00:00:00 2001 From: Zqiang Date: Mon, 1 Dec 2025 19:25:40 +0800 Subject: [PATCH] sched_ext: Fix incorrect sched_class settings for per-cpu migration tasks When loading the ebpf scheduler, the tasks in the scx_tasks list will be traversed and invoke __setscheduler_class() to get new sched_class. however, this would also incorrectly set the per-cpu migration task's->sched_class to rt_sched_class, even after unload, the per-cpu migration task's->sched_class remains sched_rt_class. The log for this issue is as follows: ./scx_rustland --stats 1 [ 199.245639][ T630] sched_ext: "rustland" does not implement cgroup cpu.weight [ 199.269213][ T630] sched_ext: BPF scheduler "rustland" enabled 04:25:09 [INFO] RustLand scheduler attached bpftrace -e 'iter:task /strcontains(ctx->task->comm, "migration")/ { printf("%s:%d->%pS\n", ctx->task->comm, ctx->task->pid, ctx->task->sched_class); }' Attaching 1 probe... migration/0:24->rt_sched_class+0x0/0xe0 migration/1:27->rt_sched_class+0x0/0xe0 migration/2:33->rt_sched_class+0x0/0xe0 migration/3:39->rt_sched_class+0x0/0xe0 migration/4:45->rt_sched_class+0x0/0xe0 migration/5:52->rt_sched_class+0x0/0xe0 migration/6:58->rt_sched_class+0x0/0xe0 migration/7:64->rt_sched_class+0x0/0xe0 sched_ext: BPF scheduler "rustland" disabled (unregistered from user space) EXIT: unregistered from user space 04:25:21 [INFO] Unregister RustLand scheduler bpftrace -e 'iter:task /strcontains(ctx->task->comm, "migration")/ { printf("%s:%d->%pS\n", ctx->task->comm, ctx->task->pid, ctx->task->sched_class); }' Attaching 1 probe... migration/0:24->rt_sched_class+0x0/0xe0 migration/1:27->rt_sched_class+0x0/0xe0 migration/2:33->rt_sched_class+0x0/0xe0 migration/3:39->rt_sched_class+0x0/0xe0 migration/4:45->rt_sched_class+0x0/0xe0 migration/5:52->rt_sched_class+0x0/0xe0 migration/6:58->rt_sched_class+0x0/0xe0 migration/7:64->rt_sched_class+0x0/0xe0 This commit therefore generate a new scx_setscheduler_class() and add check for stop_sched_class to replace __setscheduler_class(). Fixes: f0e1a0643a59 ("sched_ext: Implement BPF extensible scheduler class") Cc: stable@vger.kernel.org # v6.12+ Signed-off-by: Zqiang Reviewed-by: Andrea Righi Signed-off-by: Tejun Heo --- kernel/sched/ext.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index dca9ca0c1854..b563b8c3fd24 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -248,6 +248,14 @@ static struct scx_dispatch_q *find_user_dsq(struct scx_sched *sch, u64 dsq_id) return rhashtable_lookup(&sch->dsq_hash, &dsq_id, dsq_hash_params); } +static const struct sched_class *scx_setscheduler_class(struct task_struct *p) +{ + if (p->sched_class == &stop_sched_class) + return &stop_sched_class; + + return __setscheduler_class(p->policy, p->prio); +} + /* * scx_kf_mask enforcement. Some kfuncs can only be called from specific SCX * ops. When invoking SCX ops, SCX_CALL_OP[_RET]() should be used to indicate @@ -4241,8 +4249,7 @@ static void scx_disable_workfn(struct kthread_work *work) while ((p = scx_task_iter_next_locked(&sti))) { unsigned int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK; const struct sched_class *old_class = p->sched_class; - const struct sched_class *new_class = - __setscheduler_class(p->policy, p->prio); + const struct sched_class *new_class = scx_setscheduler_class(p); update_rq_clock(task_rq(p)); @@ -5042,8 +5049,7 @@ static int scx_enable(struct sched_ext_ops *ops, struct bpf_link *link) while ((p = scx_task_iter_next_locked(&sti))) { unsigned int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE; const struct sched_class *old_class = p->sched_class; - const struct sched_class *new_class = - __setscheduler_class(p->policy, p->prio); + const struct sched_class *new_class = scx_setscheduler_class(p); if (scx_get_task_state(p) != SCX_TASK_READY) continue; -- 2.47.3