linux-kernel - Re: [PATCH v2 2/2] pci/iov: fix kobject_uevent() ordering in sriov

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Message-ID: <Zco2pmQWR49V9Imw@kbusch-mbp.mynextlight.net>
Date: Mon, 12 Feb 2024 08:17:58 -0700
From: Keith Busch <kbusch@...nel.org>
To: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc: Jim Harris <jim.harris@...sung.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Leon Romanovsky <leonro@...dia.com>,
	Jason Gunthorpe <jgg@...dia.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	"pierre.cregut@...nge.com" <pierre.cregut@...nge.com>
Subject: Re: [PATCH v2 2/2] pci/iov: fix kobject_uevent() ordering in
 sriov_enable()

On Fri, Feb 09, 2024 at 07:22:17PM -0800, Kuppuswamy Sathyanarayanan wrote:
> On 2/9/24 3:52 PM, Jim Harris wrote:
> > @@ -677,8 +677,8 @@ static int sriov_enable(struct pci_dev *dev, int nr_virtfn)
> >  	if (rc)
> >  		goto err_pcibios;
> >  
> > -	kobject_uevent(&dev->dev.kobj, KOBJ_CHANGE);
> >  	iov->num_VFs = nr_virtfn;
> > +	kobject_uevent(&dev->dev.kobj, KOBJ_CHANGE);

Since it's accessed unlocked now, I *think* this wants appropriate
barriers to ensure the order is observed the same on all CPUs. Something
like 'smp_store_release(&iov->num_VFs, nr_virtfn)' for writing it, and
use 'smp_load_acquire()' on the read-side.