linux-kernel - Re: [PATCH v6 0/3] sched_ext: Harden scx_bpf_cpu

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Message-ID: <9025e90b-3385-467b-ac24-1b1f60767ef9@arm.com>
Date: Tue, 2 Sep 2025 14:53:56 +0100
From: Christian Loehle <christian.loehle@....com>
To: Andrea Righi <arighi@...dia.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, jake@...lion.co.uk
Subject: Re: [PATCH v6 0/3] sched_ext: Harden scx_bpf_cpu_rq()

On 9/2/25 12:58, Andrea Righi wrote:
> On Tue, Sep 02, 2025 at 12:11:40PM +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_remote_curr() that doesn't expose struct rq
>> and provide a hardened scx_bpf_cpu_rq_locked() by ensuring we hold the rq lock.
>> Add a deprecation warning to scx_bpf_cpu_rq() that mentions the two alternatives.
>>
>> This also simplifies scx code from:
>>
>> rq = scx_bpf_cpu_rq(cpu);
>> if (!rq)
>> 	return;
>> p = rq->curr
>> /* ... Do something with p */
>>
>> into:
>>
>> p = scx_bpf_remote_curr(cpu);
>> /* ... Do something with p */
> 
> This looks good to me.
> 
> We should probably add a __COMPAT_scx_bpf_remote_curr() macro, so that the
> BPF schedulers can be updated to use this new kfunc without breaking the
> compatibility with older kernels, but we can do this later, I'll send a
> follow-up patch. For now:
> 
> Acked-by: Andrea Righi <arighi@...dia.com>

Thanks!
I'd have the compat patch ready as well and would send it out in a bit.