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

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Message-ID: <aF1hMDVJcXKda_cY@localhost.localdomain>
Date: Thu, 26 Jun 2025 17:03:12 +0200
From: Frederic Weisbecker <frederic@...nel.org>
To: Bart Van Assche <bvanassche@....org>
Cc: LKML <linux-kernel@...r.kernel.org>, 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

Le Fri, Jun 20, 2025 at 08:59:58AM -0700, Bart Van Assche a écrit :
> 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.

Perhaps. "housekeeping_" doesn't match "isolation.c" but there is
already a whole set of APIs with the housekeeping prefix.

Anyway, this will likely disappear and be replaced by RCU instead.

Thanks.

-- 
Frederic Weisbecker
SUSE Labs