linux-kernel - Re: [PATCH 11/27] block: Protect against concurrent isolated cpuset change

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Message-ID: <ef9bcc7e-a726-43e1-a51e-47093589b01c@acm.org>
Date: Fri, 20 Jun 2025 08:59:58 -0700
From: Bart Van Assche <bvanassche@....org>
To: Frederic Weisbecker <frederic@...nel.org>,
 LKML <linux-kernel@...r.kernel.org>
Cc: Jens Axboe <axboe@...nel.dk>, Marco Crivellari
 <marco.crivellari@...e.com>, Michal Hocko <mhocko@...e.com>,
 Peter Zijlstra <peterz@...radead.org>, Tejun Heo <tj@...nel.org>,
 Thomas Gleixner <tglx@...utronix.de>, Vlastimil Babka <vbabka@...e.cz>,
 Waiman Long <longman@...hat.com>, linux-block@...r.kernel.org
Subject: Re: [PATCH 11/27] block: Protect against concurrent isolated cpuset
 change

On 6/20/25 8:22 AM, Frederic Weisbecker wrote:
> The block subsystem prevents running the workqueue to isolated CPUs,
> including those defined by cpuset isolated partitions. Since
> HK_TYPE_DOMAIN will soon contain both and be subject to runtime
> modifications, synchronize against housekeeping using the relevant lock.
> 
> For full support of cpuset changes, the block subsystem may need to
> propagate changes to isolated cpumask through the workqueue in the
> future.
> 
> Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
> ---
>   block/blk-mq.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 4806b867e37d..ece3369825fe 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -4237,12 +4237,16 @@ static void blk_mq_map_swqueue(struct request_queue *q)
>   
>   		/*
>   		 * Rule out isolated CPUs from hctx->cpumask to avoid
> -		 * running block kworker on isolated CPUs
> +		 * running block kworker on isolated CPUs.
> +		 * FIXME: cpuset should propagate further changes to isolated CPUs
> +		 * here.
>   		 */
> +		housekeeping_lock();
>   		for_each_cpu(cpu, hctx->cpumask) {
>   			if (cpu_is_isolated(cpu))
>   				cpumask_clear_cpu(cpu, hctx->cpumask);
>   		}
> +		housekeeping_unlock();
>   
>   		/*
>   		 * Initialize batch roundrobin counts

Isn't it expected that function names have the subsystem name as a
prefix? The function name "housekeeping_lock" is not a good name because
that name does not make it clear what subsystem that function affects.
Additionally, "housekeeping" is very vague. Please choose a better name.

Thanks,

Bart.