Re: Linux v5.5 serious PCI bug

["mika.westerberg@linux.intel.com" <mika.westerberg@linux.intel.com>]

On Mon, Dec 09, 2019 at 01:33:49PM +0000, Nicholas Johnson wrote:
> On Mon, Dec 09, 2019 at 03:12:39PM +0200, mika.westerberg@linux.intel.com wrote:
> > On Mon, Dec 09, 2019 at 12:34:04PM +0000, Nicholas Johnson wrote:
> > > Hi,
> > > 
> > > I have compiled Linux v5.5-rc1 and thought all was good until I 
> > > hot-removed a Gigabyte Aorus eGPU from Thunderbolt. The driver for the 
> > > GPU was not loaded (blacklisted) so the crash is nothing to do with the 
> > > GPU driver.
> > > 
> > > We had:
> > > - kernel NULL pointer dereference
> > > - refcount_t: underflow; use-after-free.
> > > 
> > > Attaching dmesg for now; will bisect and come back with results.
> > 
> > Looks like something related to iommu. Does it work if you disable it?
> > (intel_iommu=off in the command line).
> On Mon, Dec 09, 2019 at 03:12:39PM +0200, mika.westerberg@linux.intel.com wrote:
> > On Mon, Dec 09, 2019 at 12:34:04PM +0000, Nicholas Johnson wrote:
> > > Hi,
> > > 
> > > I have compiled Linux v5.5-rc1 and thought all was good until I 
> > > hot-removed a Gigabyte Aorus eGPU from Thunderbolt. The driver for the 
> > > GPU was not loaded (blacklisted) so the crash is nothing to do with the 
> > > GPU driver.
> > > 
> > > We had:
> > > - kernel NULL pointer dereference
> > > - refcount_t: underflow; use-after-free.
> > > 
> > > Attaching dmesg for now; will bisect and come back with results.
> > 
> > Looks like something related to iommu. Does it work if you disable it?
> > (intel_iommu=off in the command line).
> I thought it could be that, too.
> 
> The attachment "dmesg-4" from the original email is with iommu parameters.
> The attachment "dmesg-5" from the original email is with no iommu parameters.
> Attaching here "dmesg-6" with the iommu explicitly set off like you said.
> 
> No difference, still broken. Although, with iommu off, there are less stack traces.
> 
> Could it be sysfs-related?

Bisect would probably be the best option to find the culprit commit.
There are couple of commits done for pciehp so reverting them one by one
may help as well:

  87d0f2a5536f PCI: pciehp: Prevent deadlock on disconnect
  75fcc0ce72e5 PCI: pciehp: Do not disable interrupt twice on suspend
  b94ec12dfaee PCI: pciehp: Refactor infinite loop in pcie_poll_cmd()
  157c1062fcd8 PCI: pciehp: Avoid returning prematurely from sysfs requests