Re: Possible PCI Regression Linux 5.3-rc1

[Nicholas Johnson <nicholas.johnson-opensource@outlook.com.au>]

On Wed, Jul 24, 2019 at 09:48:19AM -0600, Logan Gunthorpe wrote:
> 
> 
> On 2019-07-24 7:38 a.m., Bjorn Helgaas wrote:
> > On Wed, Jul 24, 2019 at 12:54:00PM +0000, Nicholas Johnson wrote:
> >> Hi all,
> >>
> >> I was just rebasing my patches for linux 5.3-rc1 and noticed a possible 
> >> regression that shows on both of my machines. It is also reproducible 
> >> with the unmodified Ubuntu mainline kernel, downloadable at [1].
> >>
> >> Running the lspci command takes 1-3 seconds with 5.3-rc1 (rather than an 
> >> imperceivable amount of time). Booting with pci.dyndbg does not reveal 
> >> why.
> >>
> >> $ uname -r
> >> 5.3.0-050300rc1-generic
> >> $ time lspci -vt 1>/dev/null
> >>
> >> real	0m2.321s
> >> user	0m0.026s
> >> sys	0m0.000s
> >>
> >> If none of you are aware of this or what is causing it, I will submit a 
> >> bug report to Bugzilla.
> > 
> > I wasn't aware of this; thanks for reporting it!  I wasn't able to
> > reproduce this in qemu.  Can you play with "strace -r lspci -vt" and
> > the like?  Maybe try "lspci -n" to see if it's related to looking up
> > the names?
> I also just tested 5.3-rc1 on my machine and lspci behaves normally.
> 
> Logan

I have looked deeper into this and it seems that removing the 
Thunderbolt controller from the root port with sysfs resolves the issue. 
If the system you tried this on does not have Thunderbolt, then you will 
not have been able to reproduce the bug. Please see the message to Bjorn 
which you are carbon copied into for more elaboration.

Thanks for looking at this.

Regards,
Nicholas