linux-kernel - Re: [PATCH v3 0/3] sched_ext: Harden scx_bpf_cpu

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Message-ID: <aJIWHk_4IuOxyh5d@gpd4>
Date: Tue, 5 Aug 2025 16:33:02 +0200
From: Andrea Righi <arighi@...dia.com>
To: Christian Loehle <christian.loehle@....com>
Cc: tj@...nel.org, void@...ifault.com, linux-kernel@...r.kernel.org,
	sched-ext@...ts.linux.dev, changwoo@...lia.com, hodgesd@...a.com,
	mingo@...hat.com, peterz@...radead.org
Subject: Re: [PATCH v3 0/3] sched_ext: Harden scx_bpf_cpu_rq()

On Tue, Aug 05, 2025 at 12:10:33PM +0100, Christian Loehle wrote:
> scx_bpf_cpu_rq() currently allows accessing struct rq fields without
> holding the associated rq.
> It is being used by scx_cosmos, scx_flash, scx_lavd, scx_layered, and
> scx_tickless. Fortunately it is only ever used to fetch rq->curr.
> So provide an alternative scx_bpf_task_acquire_remote_curr() that
> doesn't expose struct rq and harden scx_bpf_cpu_rq() by ensuring we
> hold the rq lock.
> 
> This also simplifies scx code from:
> 
> rq = scx_bpf_cpu_rq(cpu);
> if (!rq)
> 	return;
> p = rq->curr
> if (!p)
> 	return;
> /* ... Do something with p */
> 
> into:
> 
> p = scx_bpf_tas_acquire_remote_curr(cpu);
> if (!p)
> 	return;
> /* ... Do something with p */
> bpf_task_release(p);

Looks good to me.

Reviewed-by: Andrea Righi <arighi@...dia.com>

Thanks,
-Andrea