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

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Message-Id: <20250801141741.355059-1-christian.loehle@arm.com>
Date: Fri,  1 Aug 2025 15:17:38 +0100
From: Christian Loehle <christian.loehle@....com>
To: christian.loehle@....com,
	linux-kernel@...r.kernel.org,
	sched-ext@...ts.linux.dev,
	tj@...nel.org,
	void@...ifault.com,
	arighi@...dia.com
Cc: mingo@...hat.com,
	peterz@...radead.org
Subject: [PATCH 0/3] sched_ext: Harden scx_bpf_cpu_rq()

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 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_remote_curr(cpu);
if (!p)
	return;
/* ... Do something with p */

Patch 1 was previously submitted and can be applied independently of
the other two.
https://lore.kernel.org/lkml/43a9cbdc-5121-4dc8-8438-0f01c90a4687@arm.com/
https://lore.kernel.org/lkml/0b8111c6-1b14-41dc-a674-14a6361992b3@arm.com/

Christian Loehle (3):
  sched_ext: Mark scx_bpf_cpu_rq as NULL returnable
  sched_ext: Provide scx_bpf_remote_curr()
  sched_ext: Guarantee rq lock on scx_bpf_cpu_rq()

 kernel/sched/ext.c                       | 21 ++++++++++++++++++---
 tools/sched_ext/include/scx/common.bpf.h |  1 +
 2 files changed, 19 insertions(+), 3 deletions(-)

--
2.34.1