Re: [PATCH] sched: Fix race between yield_to() and try_to_wake_up()

[Tianchen Ding]

On 2024/12/31 13:50, Tianchen Ding wrote:
> We met a SCHED_WARN in set_next_buddy():
>    __warn_printk
>    set_next_buddy
>    yield_to_task_fair
>    yield_to
>    kvm_vcpu_yield_to [kvm]
>    ...
>
> After a short dig, we found the rq_lock held by yield_to() may not
> be exactly the rq that the target task belongs to. There is a race
> window against try_to_wake_up().
>
>           CPU0                             target_task
>
>                                          blocking on CPU1
>     lock rq0 & rq1
>     double check task_rq == p_rq, ok
>                                          woken to CPU2 (lock task_pi & rq2)
>                                          task_rq = rq2
>     yield_to_task_fair (w/o lock rq2)
>
> In this race window, yield_to() is operating the task w/o the currect
Sorry... a typo for "correct"