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From: Tejun Heo <tj@kernel.org>
To: Tianyi Chen <hi@tychen.cc>
Cc: tj@kernel.org, David Vernet <void@manifault.com>,
	Andrea Righi <arighi@nvidia.com>,
	Changwoo Min <changwoo@igalia.com>, Shuah Khan <shuah@kernel.org>,
	sched-ext@lists.linux.dev, linux-kselftest@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	Emil Tsalapatis <emil@etsalapatis.com>
Subject: Re: [PATCH] selftests/sched_ext: Validate select_cpu_and mask constraints
Date: Tue, 08 Sep 2026 08:01:34 -1000	[thread overview]
Message-ID: <53d04980eecb0e5f6eeea25a5cf0dcf5@kernel.org> (raw)
In-Reply-To: <20260906144029.848978-1-hi@tychen.cc>

Hello, Tianyi.

On Sun, Sep 06, 2026 at 10:40:29PM +0800, Tianyi Chen wrote:
> +	if (cpu >= 0 &&
> +	    (!bpf_cpumask_test_cpu(cpu, cast_mask(mask)) ||
> +	     !bpf_cpumask_test_cpu(cpu, p->cpus_ptr)))
> +		cpu = -ERANGE;

The syscall runs with migration disabled. With CONFIG_PREEMPT_RCU,
preemption between selection and this check can make
migrate_disable_switch() narrow p->cpus_ptr to the running CPU, rejecting a
valid selection on another CPU. Please check the requested affinity instead.

> +	SCX_FAIL_IF(sched_getaffinity(0, sizeof(original), &original),
> +		    "Failed to get affinity (%d)", errno);

Please use dynamically allocated masks. The fixed cpu_set_t makes
sched_getaffinity() fail with EINVAL when nr_cpu_ids exceeds 1024, even if
the task only uses low-numbered CPUs.

Thanks.
-- 
tejun

      reply	other threads:[~2026-09-08 18:05 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-09-06 14:40 Tianyi Chen
2026-09-08 18:01 ` Tejun Heo [this message]

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