Re: [PATCH] sched: add READ_ONCE to task_on_rq_queued

[Phil Auld]

On Thu, Nov 14, 2024 at 09:21:28AM -0700 Jon Kohler wrote:
> task_on_rq_queued read p->on_rq without READ_ONCE, though p->on_rq is
> set with WRITE_ONCE in {activate|deactivate}_task and smp_store_release
> in __block_task, and also read with READ_ONCE in task_on_rq_migrating.
> 
> Make all of these accesses pair together by adding READ_ONCE in the
> task_on_rq_queued.
> 
> Signed-off-by: Jon Kohler <jon@xxxxxxxxxxx>
> ---
>  kernel/sched/sched.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index c03b3d7b320e..dbbe5ce0dd96 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -2277,7 +2277,7 @@ static inline int task_on_cpu(struct rq *rq, struct task_struct *p)
>  
>  static inline int task_on_rq_queued(struct task_struct *p)
>  {
> -	return p->on_rq == TASK_ON_RQ_QUEUED;
> +	return READ_ONCE(p->on_rq) == TASK_ON_RQ_QUEUED;
>  }
>  
>  static inline int task_on_rq_migrating(struct task_struct *p)
> -- 
> 2.43.0
> 
> 

That looks right especially when seen with task_on_rq_migrating()
right below it, as you said.

Reviewed-by: Phil Auld <pauld@xxxxxxxxxx>


Cheers,
Phil
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