linux-kernel - Re: [PATCH 03/27] PCI: Protect against concurrent change of housekeeping cpumask

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Message-ID: <20250620161710.GA1296438@bhelgaas>
Date: Fri, 20 Jun 2025 11:17:10 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Frederic Weisbecker <frederic@...nel.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	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>
Subject: Re: [PATCH 03/27] PCI: Protect against concurrent change of
 housekeeping cpumask

On Fri, Jun 20, 2025 at 05:22:44PM +0200, Frederic Weisbecker wrote:
> HK_TYPE_DOMAIN will soon integrate cpuset isolated partitions and
> therefore be made modifyable at runtime. Synchronize against the cpumask
> update using appropriate locking.

s/modifyable/modifiable/

> Queue and wait for the PCI call to complete while holding the
> housekeeping rwsem. This way the housekeeping update side doesn't need
> to propagate its changes to PCI.

What PCI call are we waiting for?  I see housekeeping_lock(), but I
assume that's doing some housekeeping-related mutual exclusion, not
waiting for PCI work.

I don't know how to use housekeeping_lock() or when it's needed.  Can
you add some guidance here and at the housekeeping_lock() definition?

> Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
> ---
>  drivers/pci/pci-driver.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index 67db34fd10ee..459d211a408b 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -362,7 +362,7 @@ static int pci_call_probe(struct pci_driver *drv, struct pci_dev *dev,
>  	dev->is_probed = 1;
>  
>  	cpu_hotplug_disable();
> -
> +	housekeeping_lock();
>  	/*
>  	 * Prevent nesting work_on_cpu() for the case where a Virtual Function
>  	 * device is probed from work_on_cpu() of the Physical device.
> @@ -392,6 +392,7 @@ static int pci_call_probe(struct pci_driver *drv, struct pci_dev *dev,
>  		error = local_pci_probe(&ddi);
>  out:
>  	dev->is_probed = 0;
> +	housekeeping_unlock();
>  	cpu_hotplug_enable();
>  	return error;
>  }
> -- 
> 2.48.1
>