netdev - Re: [PATCH 01/33] PCI: Prepare to protect against concurrent isolated cpuset change

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Message-ID: <20260122161419.GA1250200@bhelgaas>
Date: Thu, 22 Jan 2026 10:14:19 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Frederic Weisbecker <frederic@...nel.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
	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>,
	Jens Axboe <axboe@...nel.dk>, 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 01/33] PCI: Prepare to protect against concurrent
 isolated cpuset change

On Thu, Jan 01, 2026 at 11:13:26PM +0100, Frederic Weisbecker wrote:
> HK_TYPE_DOMAIN will soon integrate cpuset isolated partitions and
> therefore be made modifiable at runtime. Synchronize against the cpumask
> update using RCU.
> 
> The RCU locked section includes both the housekeeping CPU target
> election for the PCI probe work and the work enqueue.
> 
> This way the housekeeping update side will simply need to flush the
> pending related works after updating the housekeeping mask in order to
> make sure that no PCI work ever executes on an isolated CPU. This part
> will be handled in a subsequent patch.
> 
> Signed-off-by: Frederic Weisbecker <frederic@...nel.org>

Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>

> ---
>  drivers/pci/pci-driver.c | 47 ++++++++++++++++++++++++++++++++--------
>  1 file changed, 38 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index 7c2d9d596258..a6111140755c 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -302,9 +302,8 @@ struct drv_dev_and_id {
>  	const struct pci_device_id *id;
>  };
>  
> -static long local_pci_probe(void *_ddi)
> +static int local_pci_probe(struct drv_dev_and_id *ddi)
>  {
> -	struct drv_dev_and_id *ddi = _ddi;
>  	struct pci_dev *pci_dev = ddi->dev;
>  	struct pci_driver *pci_drv = ddi->drv;
>  	struct device *dev = &pci_dev->dev;
> @@ -338,6 +337,19 @@ static long local_pci_probe(void *_ddi)
>  	return 0;
>  }
>  
> +struct pci_probe_arg {
> +	struct drv_dev_and_id *ddi;
> +	struct work_struct work;
> +	int ret;
> +};
> +
> +static void local_pci_probe_callback(struct work_struct *work)
> +{
> +	struct pci_probe_arg *arg = container_of(work, struct pci_probe_arg, work);
> +
> +	arg->ret = local_pci_probe(arg->ddi);
> +}
> +
>  static bool pci_physfn_is_probed(struct pci_dev *dev)
>  {
>  #ifdef CONFIG_PCI_IOV
> @@ -362,34 +374,51 @@ static int pci_call_probe(struct pci_driver *drv, struct pci_dev *dev,
>  	dev->is_probed = 1;
>  
>  	cpu_hotplug_disable();
> -
>  	/*
>  	 * Prevent nesting work_on_cpu() for the case where a Virtual Function
>  	 * device is probed from work_on_cpu() of the Physical device.
>  	 */
>  	if (node < 0 || node >= MAX_NUMNODES || !node_online(node) ||
>  	    pci_physfn_is_probed(dev)) {
> -		cpu = nr_cpu_ids;
> +		error = local_pci_probe(&ddi);
>  	} else {
>  		cpumask_var_t wq_domain_mask;
> +		struct pci_probe_arg arg = { .ddi = &ddi };
>  
>  		if (!zalloc_cpumask_var(&wq_domain_mask, GFP_KERNEL)) {
>  			error = -ENOMEM;
>  			goto out;
>  		}
> +
> +		INIT_WORK_ONSTACK(&arg.work, local_pci_probe_callback);
> +
> +		/*
> +		 * The target election and the enqueue of the work must be within
> +		 * the same RCU read side section so that when the workqueue pool
> +		 * is flushed after a housekeeping cpumask update, further readers
> +		 * are guaranteed to queue the probing work to the appropriate
> +		 * targets.
> +		 */
> +		rcu_read_lock();
>  		cpumask_and(wq_domain_mask,
>  			    housekeeping_cpumask(HK_TYPE_WQ),
>  			    housekeeping_cpumask(HK_TYPE_DOMAIN));
>  
>  		cpu = cpumask_any_and(cpumask_of_node(node),
>  				      wq_domain_mask);
> +		if (cpu < nr_cpu_ids) {
> +			schedule_work_on(cpu, &arg.work);
> +			rcu_read_unlock();
> +			flush_work(&arg.work);
> +			error = arg.ret;
> +		} else {
> +			rcu_read_unlock();
> +			error = local_pci_probe(&ddi);
> +		}
> +
>  		free_cpumask_var(wq_domain_mask);
> +		destroy_work_on_stack(&arg.work);
>  	}
> -
> -	if (cpu < nr_cpu_ids)
> -		error = work_on_cpu(cpu, local_pci_probe, &ddi);
> -	else
> -		error = local_pci_probe(&ddi);
>  out:
>  	dev->is_probed = 0;
>  	cpu_hotplug_enable();
> -- 
> 2.51.1
>