linux-kernel - Re: [PATCH v5 3/3] sched_ext: deprecation warn for scx_bpf_cpu

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Message-ID: <8559c7d7-2171-4d86-8334-7e8442e96b9a@arm.com>
Date: Wed, 3 Sep 2025 21:37:54 +0100
From: Christian Loehle <christian.loehle@....com>
To: Tejun Heo <tj@...nel.org>
Cc: arighi@...dia.com, 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 v5 3/3] sched_ext: deprecation warn for scx_bpf_cpu_rq()

On 9/3/25 16:56, Tejun Heo wrote:
> On Mon, Sep 01, 2025 at 02:26:04PM +0100, Christian Loehle wrote:
>> scx_bpf_cpu_rq() works on an unlocked rq which generally isn't safe.
>> For the common use-cases scx_bpf_cpu_rq_locked() and
>> scx_bpf_remote_curr() work, so add a deprecation warning
>> to scx_bpf_cpu_rq() so it can eventually be removed.
>>
>> Signed-off-by: Christian Loehle <christian.loehle@....com>
>> ---
>>  kernel/sched/ext.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
>> index e242a2520f06..a524d404ad09 100644
>> --- a/kernel/sched/ext.c
>> +++ b/kernel/sched/ext.c
>> @@ -7427,6 +7427,9 @@ __bpf_kfunc struct rq *scx_bpf_cpu_rq(s32 cpu)
>>  	if (!kf_cpu_valid(cpu, NULL))
>>  		return NULL;
>>  
>> +	pr_warn_once("%s() is deprecated; use scx_bpf_cpu_rq_locked() when holding rq lock "
>> +		     "or scx_bpf_remote_curr() to read remote curr safely.\n", __func__);
>> +
> 
> I wonder whether it'd make more sense to tie the once testing to the
> scheduler instance (see warned_zero_slice).
> 
Yes that makes sense to me, I'll resend with this and the renaming suggestions.
Thanks!