Received-SPF: pass (google.com: domain of linux-kernel+bounces-1733-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45e3:2400::1 as permitted sender) client-ip=2604:1380:45e3:2400::1;
From: Jim Harris <jim.harris@samsung.com>
To: Bjorn Helgaas <helgaas@kernel.org>
CC: 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>
Subject: Re: [PATCH] pci/iov: fix kobject_uevent() ordering in
 sriov_enable()
Thread-Topic: [PATCH] pci/iov: fix kobject_uevent() ordering in
	sriov_enable()
Thread-Index: AQHaLfZbfzSE7OYN20WpA0TR5aL0dLCoHtUAgANSmoA=
Date: Fri, 15 Dec 2023 22:11:17 +0000
Message-ID: <ZXzPBTZ2rK/CPy5o@ubuntu>
In-Reply-To: <20231213192652.GA1054534@bhelgaas>
Accept-Language: en-US
Content-Language: en-US
Content-Type: text/plain; charset="us-ascii"
Content-ID: <A9BE0741C2887B4194448243347D1463@ssi.samsung.com>
Content-Transfer-Encoding: quoted-printable
Precedence: bulk
MIME-Version: 1.0
CMS-TYPE: 301P
References: <170249390826.436889.13896090394795622449.stgit@bgt-140510-bm01.eng.stellus.in>
	<20231213192652.GA1054534@bhelgaas>
	<CGME20231215221118uscas1p1b407f67deb53a75ae03d67247653b30b@uscas1p1.samsung.com>

On Wed, Dec 13, 2023 at 01:26:52PM -0600, Bjorn Helgaas wrote:
> On Wed, Dec 13, 2023 at 06:58:28PM +0000, Jim Harris wrote:
> > Wait to call kobject_uevent() until all of the associated changes are d=
one,
> > including updating the num_VFs value.
>=20
> This seems right to me.  Can we add a little rationale to the commit
> log?  E.g., something about how num_VFs is visible to userspace via
> sysfs and we don't want a race between (a) userspace reading num_VFs
> because of KOBJ_CHANGE and (b) the kernel updating num_VFs?  (If
> that's the actual reason.)
>=20
> If there's a problem report about this, include that reference as
> well.

There's a second patch that I haven't pushed yet that has more of the
rationale that led to this suggestion from Leon - see thread
"Locking between vfio hot-remove..." I'll push the two patches as a series.

The second patch will effectively revert 35ff867b7, since Leon felt the
reasoning behind that patch was incorrect. I'll tie all of that into the
cover letter.

-Jim

>=20
> > Suggested by: Leon Romanovsky <leonro@nvidia.com>
> > Signed-off-by: Jim Harris <jim.harris@samsung.com>
> > ---
> >  drivers/pci/iov.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >=20
> > diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
> > index 25dbe85c4217..3b768e20c7ab 100644
> > --- a/drivers/pci/iov.c
> > +++ b/drivers/pci/iov.c
> > @@ -683,8 +683,8 @@ static int sriov_enable(struct pci_dev *dev, int nr=
_virtfn)
> >  	if (rc)
> >  		goto err_pcibios;
> > =20
> > -	kobject_uevent(&dev->dev.kobj, KOBJ_CHANGE);
> >  	iov->num_VFs =3D nr_virtfn;
> > +	kobject_uevent(&dev->dev.kobj, KOBJ_CHANGE);
> > =20
> >  	return 0;
> > =20
> > =