Re: [dpdk-dev] [PATCH 1/3] bus/pci: update device devargs on each rescan

["Gaëtan Rivet" <gaetan.rivet@6wind.com>]

On Mon, Nov 05, 2018 at 02:52:00PM +0000, Stojaczyk, Dariusz wrote:
> Hi Gaetan,
> 
> > -----Original Message-----
> > From: Gaëtan Rivet [mailto:gaetan.rivet@6wind.com]
> > Subject: Re: [dpdk-dev] [PATCH 1/3] bus/pci: update device devargs on each
> > rescan
> > 
> > Hi Darek,
> > 
> > On Mon, Nov 05, 2018 at 08:04:45AM +0100, Darek Stojaczyk wrote:
> > > Bus rescan is done e.g. during the device hotplug,
> > > where devargs are re-allocated. By not updating the
> > > rte_device->devargs pointer we potentially make it
> > > a dangling one, as previous devargs could have been
> > > (or will be soon) freed.
> > >
> > > Fixes: 55e411b301c3 ("bus/pci: fix resource mapping override")
> > > Cc: qi.z.zhang@intel.com
> > >
> > > Signed-off-by: Darek Stojaczyk <dariusz.stojaczyk@intel.com>
> > > ---
> > >  drivers/bus/pci/linux/pci.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/bus/pci/linux/pci.c b/drivers/bus/pci/linux/pci.c
> > > index f87533c5c..f3172960e 100644
> > > --- a/drivers/bus/pci/linux/pci.c
> > > +++ b/drivers/bus/pci/linux/pci.c
> > > @@ -349,10 +349,10 @@ pci_scan_one(const char *dirname, const struct
> > rte_pci_addr *addr)
> > >  			if (ret < 0) {
> > >  				rte_pci_insert_device(dev2, dev);
> > >  			} else { /* already registered */
> > > +				pci_name_set(dev2);
> > 
> > This is rather unfortunate to call pci_name_set()
> > to trigger the mapping devargs <-> devices.
> > 
> > pci_devargs_lookup could be made non-static instead,
> > if that's sufficient. 
> 
> This is unfortunately trigerred by the generic eal device hotplug path which looks as follows:
> 
> da = calloc(sizeof rte_devargs);
> [...]
> rte_devargs_insert(da); # frees the previous devargs that rte_device still references
> da->bus->scan(); # this should update the dangling devargs/name pointer in rte_device
> 
> Instead of making pci_devargs_lookup public, we would have to introduce a new bus callback for updating devargs of only a single device and that would be a really, realy ugly overkill. Thomas already mentioned in the subsequent patch within this series that we might want to re-think the devargs design in the next release.
> 

No, of course, I'm not saying to make pci_devargs_lookup public, only
private to the PCI bus, and within the bus, non-static. This way,
instead of calling pci_name_set(), you call instead only
pci_devargs_lookup().

> > Given that the PCI id matches because the device
> > is a duplicate (already registered), then the name itself probably does
> > not need to be updated.
> 
> The issue here was that old devargs/name could have been freed.
> The new name is the same as the old one, it's just in a different buffer.
> 
> I know calling pci_name_set() on each device during scan is not perfect, but IMO it's enforced by the current rte_devargs design. Besides, this used to be the original behavior before 55e411b301c3 ("bus/pci: fix resource mapping override").
> 
> Thanks,
> D.
> 
> > 
> > >  <snip>
> > 
> > --
> > Gaëtan Rivet
> > 6WIND

-- 
Gaëtan Rivet
6WIND