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@arm.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__);
+
 	return cpu_rq(cpu);
 }
 
-- 
2.34.1

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@arm.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).

Thanks.

-- 
tejun

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@arm.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!