linux-kernel - Re: [PATCH 09/33] block: Protect against concurrent isolated cpuset change

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Message-ID: <0f65c4fe-8b10-403d-b5b6-ed33fc4eb69c@kernel.dk>
Date: Mon, 29 Dec 2025 17:37:29 -0700
From: Jens Axboe <axboe@...nel.dk>
To: Frederic Weisbecker <frederic@...nel.org>,
 LKML <linux-kernel@...r.kernel.org>
Cc: Michal Koutný <mkoutny@...e.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Bjorn Helgaas <bhelgaas@...gle.com>,
 Catalin Marinas <catalin.marinas@....com>,
 Chen Ridong <chenridong@...wei.com>, Danilo Krummrich <dakr@...nel.org>,
 "David S . Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Gabriele Monaco <gmonaco@...hat.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Ingo Molnar <mingo@...hat.com>, Jakub Kicinski <kuba@...nel.org>,
 Johannes Weiner <hannes@...xchg.org>, Lai Jiangshan
 <jiangshanlai@...il.com>, Marco Crivellari <marco.crivellari@...e.com>,
 Michal Hocko <mhocko@...e.com>, Muchun Song <muchun.song@...ux.dev>,
 Paolo Abeni <pabeni@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
 Phil Auld <pauld@...hat.com>, "Rafael J . Wysocki" <rafael@...nel.org>,
 Roman Gushchin <roman.gushchin@...ux.dev>,
 Shakeel Butt <shakeel.butt@...ux.dev>, Simon Horman <horms@...nel.org>,
 Tejun Heo <tj@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
 Vlastimil Babka <vbabka@...e.cz>, Waiman Long <longman@...hat.com>,
 Will Deacon <will@...nel.org>, cgroups@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-block@...r.kernel.org,
 linux-mm@...ck.org, linux-pci@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH 09/33] block: Protect against concurrent isolated cpuset
 change

On 12/24/25 6:44 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 1978eef95dca..0037af1216f3 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -4257,12 +4257,16 @@ 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.
>  		 */
> +		rcu_read_lock();
>  		for_each_cpu(cpu, hctx->cpumask) {
>  			if (cpu_is_isolated(cpu))
>  				cpumask_clear_cpu(cpu, hctx->cpumask);
>  		}
> +		rcu_read_unlock();

Want me to just take this one separately and get it out of your hair?
Doesn't seem to have any dependencies.

-- 
Jens Axboe