Re: [PATCH] pci/sriov: Hold rescan lock while enumerating

[Bjorn Helgaas <helgaas@kernel.org>]

[+cc Lukas, -stable]

On Thu, Aug 09, 2018 at 10:33:56AM -0600, Keith Busch wrote:
> PCI enumeration/de-enumeration needs to run single threaded to prevent
> race conditions with other threads changing the topology. Altering the
> number of virtual functions was not taking the rescan/remove lock hile
> adding or removing those virtual functions, so this patch adds that.
> 
> Reported-by: Krzysztof Wierzbicki <krzysztof.wierzbicki@intel.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: Keith Busch <keith.busch@intel.com>
> ---
>  drivers/pci/pci-sysfs.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index 9ecfe13157c0..611abe220b6f 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -591,6 +591,7 @@ static ssize_t sriov_numvfs_store(struct device *dev,
>  	if (num_vfs > pci_sriov_get_totalvfs(pdev))
>  		return -ERANGE;
>  
> +	pci_lock_rescan_remove();

I assume the usual path is something like this, where we end up in
pci_enable_sriov():

  sriov_numvfs_store
+   pci_lock_rescan_remove
    pdev->driver->sriov_configure
      ...
        pci_enable_sriov
          sriov_enable
            pci_iov_add_virtfn
              pci_alloc_dev
              pci_device_add

But what about the other paths leading to pci_iov_add_virtfn()?  Don't
we need similar locking for all of them?  

>  	device_lock(&pdev->dev);
>  
>  	if (num_vfs == pdev->sriov->num_VFs)
> @@ -627,6 +628,7 @@ static ssize_t sriov_numvfs_store(struct device *dev,
>  
>  exit:
>  	device_unlock(&pdev->dev);
> +	pci_unlock_rescan_remove();
>  
>  	if (ret < 0)
>  		return ret;
> -- 
> 2.14.4
>