linux-kernel - Re: [PATCH sched_ext/for-6.15 v3 3/5] sched_ext: Add scx_kfunc_ids_ops_context_sensitive for unified filtering of context-sensitive SCX kfuncs

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Message-ID: <Z8InUDxSbSR_d3kk@slm.duckdns.org>
Date: Fri, 28 Feb 2025 11:14:56 -1000
From: Tejun Heo <tj@...nel.org>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Juntong Deng <juntong.deng@...look.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	John Fastabend <john.fastabend@...il.com>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>, Eddy Z <eddyz87@...il.com>,
	Song Liu <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>,
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>,
	Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
	Kumar Kartikeya Dwivedi <memxor@...il.com>,
	David Vernet <void@...ifault.com>, Andrea Righi <arighi@...dia.com>,
	Changwoo Min <changwoo@...lia.com>, bpf <bpf@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH sched_ext/for-6.15 v3 3/5] sched_ext: Add
 scx_kfunc_ids_ops_context_sensitive for unified filtering of
 context-sensitive SCX kfuncs

Hello,

On Thu, Feb 27, 2025 at 06:38:32PM -0800, Alexei Starovoitov wrote:
...
> > > Not from this change but these can probably be allowed from TRACING too.
> > >
> >
> > Not sure if it is safe to make these kfuncs available in TRACING.
> > If Alexei sees this email, could you please leave a comment?
> 
> Hold on, you want to enable all of scx_kfunc_ids_unlocked[] set
> to all of TRACING ? What is the use case ?

I thought it may be useful to be able to iterate DSQs and trigger
dispatching from there but

> Maybe it's safe, but without in-depth analysis we shouldn't.
> Currently sched-ext allows scx_kfunc_set_any[] for tracing.
> I would stick to that in this patch set.

I haven't thought through about safety at all and was mostly naively
thinking that if _any is safe _unlocked should too. Right now, unlocked has
two groups of kfuncs - the ones that should be able to sleep and the ones
that can be called from within scx_dsq_iter iterations. The former is
excluded from TRACING through KF_SLEEPABLE, I think. I don't know whether
dsq iteration is allowed in TRACING.

Anyways, not a real issue either way.

Thanks.

-- 
tejun