Re: [dpdk-dev] [PATCH] eal: fix to set the rte_device ptr's device args before hotplug

[Somnath Kotur <somnath.kotur@broadcom.com>]

On Tue, Feb 11, 2020 at 2:08 PM Gaetan Rivet <grive@u256.net> wrote:
>
> [...]
> >>> (gdb) p dev2
> >>> $5 = (struct rte_pci_device *) 0x54de5e0
> >>> (gdb) p /x *dev2
> >>> $6 = {next = {tqe_next = 0x5307460, tqe_prev = 0x5539f80}, device =
> >>> {next = {tqe_next = 0x0, tqe_prev = 0x0}, name = 0x54e4f00, driver =
> >>> 0x3a6b7f0,
> >>>       bus = 0x3a59a00, numa_node = 0x0, devargs = 0x0}, addr = {domain =
> >>> 0x0, bus = 0x6, devid = 0x2, function = 0x0}
> >>>
> >>> we hit the pci_device ( 0x54de5e0) that was created during the first
> >>> time probe of the parent device ?
> >>> Since it is already probed, it goes to line 381 where it does frees
> >>> the just allocated 'pci_device'  inside pci_scan_one() via 'free(dev)'
> >>>
> >>> As you can see this pci_device does not have it's devargs set (rightly
> >>> so as initially there were no devargs for this device)
> >>>
> >>> But as shown in the stack trace in my previous reply, when
> >>> pci_find_device() walks the rte_pci_devices list , it finds this
> >>> earlier probed device (without devargs)
> >>>
> >>
> >> Alright, I think you are right, this is what is happening.
> >> The issue IMO, is that the PCI scan is thus hitting an already existing device, but we have
> >> missed the case where the new device has more info that the previous one (linked devargs).
> >>
> > That is correct
> >
> >>> pci_find_device (start=0x0, cmp=0x4b92d8 <cmp_dev_name>,
> >>> data=0x55a4af8) at /root/dpdk-19.11/drivers/bus/pci/pci_common.c:426
> >>> 426                             return &pdev->device;
> >>> (gdb) p pdev
> >>> $15 = (struct rte_pci_device *) 0x54de5e0
> >>>
> >>> (gdb) p /x *pdev
> >>> $16 = {next = {tqe_next = 0x5307460, tqe_prev = 0x5539f80}, device =
> >>> {next = {tqe_next = 0x0, tqe_prev = 0x0}, name = 0x54e4f00, driver =
> >>> 0x3a6b7f0,
> >>>       bus = 0x3a59a00, numa_node = 0x0, devargs = 0x0}, addr = {domain =
> >>> 0x0, bus = 0x6, devid = 0x2, function = 0x0},
> >>>
> >>> Hope this explains why the pci_device has NULL devargs at this point
> >>> and how my fix to set it at this point helps solve the problem?
> >>>
> >>> Please let me know your thoughts
> >>>
> >>
> >> I think the proper fix is instead to have a clean update during the PCI scan.
> >> The proper way is to keep the old device, but override its fields as new info was found.
> >
> > Agreed
> >>
> >> Something like calling pci_name_set(dev2); line 359 maybe. BSD should also be updated for consistency.
> >>
> >> My issue with your patch is that I think this issue is very specific to the PCI bus and the capabilities
> >> of some devices on it. It would be better to have a fully compliant scan + probe ops considering
> >> the supported capabilities, instead of forcing this on all buses.
> > Sure, so i'm guessing you meant something like this ?
> >
> > dex 740a2cd..92a41c2 100644
> > --- a/drivers/bus/pci/linux/pci.c
> > +++ b/drivers/bus/pci/linux/pci.c
> > @@ -377,6 +377,8 @@
> >                                                   */
> >                                                  RTE_LOG(ERR, EAL,
> > "Unexpected device scan at %s!\n",
> >                                                          filename);
> > +                                       else if (dev2->device.devargs
> > != dev->device.devargs)
> > +                                               pci_name_set(dev2);
> >                                  }
> >                                  free(dev);
> >                          }
> >
> > Which is basically checking for devargs mismatch between the 'new'
> > device and a match with an
> > already probed device and  return the old device while adjusting the
> > new info (devargs)
> > Is that OK?
> >
> >>
> >> I'm wondering whether this can happen with an already existing devargs? If so, is it more correct to keep
> >> the new one, or ignore the probe, free the new devargs and report an error? If the former,
> >> please clean up properly the devargs using rte_devargs_remove() (before calling pci_name_set() of course).
>
> Hello Somnath,
>
> Yes, this is basically it, however you also need to take care of a potential already existing devargs here, because the PCI bus does not guarantee that all devargs of a device will be named the same
Thanks a lot Gaetan, have sent out V2 incorporating your suggestions
here.. Please ack


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