On Tue, Oct 22, 2024 at 03:40:52PM +0200, Marco Elver wrote:
> Which gives us:
>
> | ==================================================================
> | BUG: KCSAN: assert: race in dequeue_entities / ttwu_do_activate
> |
> | write (marked) to 0xffff9e100329c628 of 4 bytes by interrupt on cpu 0:
> | activate_task kernel/sched/core.c:2064 [inline]
>
> This is this one:
>
> void activate_task(struct rq *rq, struct task_struct *p, int flags)
> {
> if (task_on_rq_migrating(p))
> flags |= ENQUEUE_MIGRATED;
> if (flags & ENQUEUE_MIGRATED)
> sched_mm_cid_migrate_to(rq, p);
>
> enqueue_task(rq, p, flags);
>
> WRITE_ONCE(p->on_rq, TASK_ON_RQ_QUEUED);
> ASSERT_EXCLUSIVE_WRITER(p->on_rq);
> }
>
> | ttwu_do_activate+0x153/0x3e0 kernel/sched/core.c:3671
> | ttwu_queue kernel/sched/core.c:3944 [inline]
> | try_to_wake_up+0x60f/0xaf0 kernel/sched/core.c:4270
> | assert no writes to 0xffff9e100329c628 of 4 bytes by task 10571 on cpu 3:
> | __block_task kernel/sched/sched.h:2770 [inline]
>
> And that's:
>
> static inline void __block_task(struct rq *rq, struct task_struct *p)
> {
> WRITE_ONCE(p->on_rq, 0);
> ASSERT_EXCLUSIVE_WRITER(p->on_rq);
> if (p->sched_contributes_to_load)
> rq->nr_uninterruptible++;
>
> | dequeue_entities+0xd83/0xe70 kernel/sched/fair.c:7177
> | pick_next_entity kernel/sched/fair.c:5627 [inline]
> | pick_task_fair kernel/sched/fair.c:8856 [inline]
> | pick_next_task_fair+0xaf/0x710 kernel/sched/fair.c:8876
> | __pick_next_task kernel/sched/core.c:5955 [inline]
> | pick_next_task kernel/sched/core.c:6477 [inline]
> | __schedule+0x47a/0x1130 kernel/sched/core.c:6629
> | __schedule_loop kernel/sched/core.c:6752 [inline]
> | schedule+0x7b/0x130 kernel/sched/core.c:6767
So KCSAn is trying to tell me these two paths run concurrently on the
same 'p' ?!? That would be a horrible bug -- both these call chains
should be holding rq->__lock (for task_rq(p)).
