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

[Bjorn Helgaas <helgaas@kernel.org>]

On Wed, Sep 05, 2018 at 03:12:41PM -0600, Keith Busch wrote:
> On Wed, Sep 05, 2018 at 03:58:40PM -0500, Bjorn Helgaas wrote:
> > [+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?  
> 
> Good point. It looks like the only other path to pci_iov_add_virtfn is
> through PPC eeh_reset_device, which coincidently enough already holds
> pci_lock_rescan_remove.

There are a few .probe() methods that call pci_enable_sriov(), which leads
to pci_iov_add_virtfn():

  cavium_rng_probe
  cpt_probe
  enic_probe
  be_probe -> be_setup -> be_vf_setup
  igb_probe -> igb_sw_init -> igb_probe_vfs -> igb_enable_sriov
  ...

> It's not just pci_iov_add_virtfn, though. We also need to hold it during
> pci_iov_remove_virtfn. PPC eeh_rmv_device is not holding the lock in
> that path. I'll never be able to test with that h/w, but I'll look at it.
> 
> > >  	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
> > >