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Message-Id: <20250804112743.711816-1-christian.loehle@arm.com>
Date: Mon, 4 Aug 2025 12:27:40 +0100
From: Christian Loehle <christian.loehle@....com>
To: tj@...nel.org,
arighi@...dia.com,
void@...ifault.com
Cc: linux-kernel@...r.kernel.org,
sched-ext@...ts.linux.dev,
changwoo@...lia.com,
hodgesd@...a.com,
mingo@...hat.com,
peterz@...radead.org,
Christian Loehle <christian.loehle@....com>
Subject: [PATCH v2 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 */
bpf_task_release(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/
v1:
https://lore.kernel.org/lkml/20250801141741.355059-1-christian.loehle@arm.com/
- scx_bpf_cpu_rq() now errors when a not locked rq is requested. (Andrea)
- scx_bpf_remote_curr() calls bpf_task_acquire() which BPF user needs to
release. (Andrea)
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 | 36 ++++++++++++++++++++++--
tools/sched_ext/include/scx/common.bpf.h | 1 +
2 files changed, 35 insertions(+), 2 deletions(-)
--
2.34.1
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