linux-kernel - Re: [PATCH-cgroup 2/2] cgroup/cpuset: Include isolated cpuset CPUs in cpu_is

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Date:   Tue, 28 Nov 2023 06:56:08 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        Mrunal Patel <mpatel@...hat.com>,
        Ryan Phillips <rphillips@...hat.com>,
        Brent Rowsell <browsell@...hat.com>,
        Peter Hunt <pehunt@...hat.com>
Subject: Re: [PATCH-cgroup 2/2] cgroup/cpuset: Include isolated cpuset CPUs
 in cpu_is_isolated() check

Hello,

On Sun, Nov 26, 2023 at 11:19:56PM -0500, Waiman Long wrote:
> +bool cpuset_cpu_is_isolated(int cpu)
> +{
> +	unsigned int seq;
> +	bool ret;
> +
> +	do {
> +		seq = read_seqcount_begin(&isolcpus_seq);
> +		ret = cpumask_test_cpu(cpu, isolated_cpus);
> +	} while (read_seqcount_retry(&isolcpus_seq, seq));
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(cpuset_cpu_is_isolated);

We're testing a bit in a bitmask. I don't think we need to worry about value
integrity from RMW updates being broken up. ie. We can just test the bit
without seqlock and drop the first patch?

Thanks.

-- 
tejun