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Date: Mon, 12 Feb 2024 08:17:58 -0700
From: Keith Busch <kbusch@kernel.org>
To: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Cc: Jim Harris <jim.harris@samsung.com>,
	Bjorn Helgaas <bhelgaas@google.com>,
	"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Leon Romanovsky <leonro@nvidia.com>,
	Jason Gunthorpe <jgg@nvidia.com>,
	Alex Williamson <alex.williamson@redhat.com>,
	"pierre.cregut@orange.com" <pierre.cregut@orange.com>
Subject: Re: [PATCH v2 2/2] pci/iov: fix kobject_uevent() ordering in
 sriov_enable()
Message-ID: <Zco2pmQWR49V9Imw@kbusch-mbp.mynextlight.net>
References: <170752254154.1693615.9176696143128338408.stgit@bgt-140510-bm01.eng.stellus.in>
 <CGME20240209235218uscas1p2d0978af6623037fa1b9358a2ad2320c5@uscas1p2.samsung.com>
 <170752273749.1693615.1293677023514112939.stgit@bgt-140510-bm01.eng.stellus.in>
 <d9c89ad1-990d-4a4c-a16d-27d978673e57@linux.intel.com>
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In-Reply-To: <d9c89ad1-990d-4a4c-a16d-27d978673e57@linux.intel.com>

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.