Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:7 as permitted sender) client-ip=2620:137:e000::3:7;
Date:   Wed, 13 Dec 2023 13:26:52 -0600
From:   Bjorn Helgaas <helgaas@kernel.org>
To:     Jim Harris <jim.harris@samsung.com>
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()
Message-ID: <20231213192652.GA1054534@bhelgaas>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <170249390826.436889.13896090394795622449.stgit@bgt-140510-bm01.eng.stellus.in>
Precedence: bulk

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 done,
> including updating the num_VFs value.

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.)

If there's a problem report about this, include that reference as
well.

> 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(-)
> 
> 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;
>  
> -	kobject_uevent(&dev->dev.kobj, KOBJ_CHANGE);
>  	iov->num_VFs = nr_virtfn;
> +	kobject_uevent(&dev->dev.kobj, KOBJ_CHANGE);
>  
>  	return 0;
>  
>