Dan Williams <dan.j.williams@xxxxxxxxx> writes:
> While the experiment did reveal that there are additional places that
> are missing the lock during secondary bus reset, one of the places that
> needs to take cfg_access_lock (pci_bus_lock()) is not prepared for
> lockdep annotation.
>
> Specifically, pci_bus_lock() takes pci_dev_lock() recursively and is
> currently dependent on the fact that the device_lock() is marked
> lockdep_set_novalidate_class(&dev->mutex). Otherwise, without that
> annotation, pci_bus_lock() would need to use something like a new
> pci_dev_lock_nested() helper, a scheme to track a PCI device's depth in
> the topology, and a hope that the depth of a PCI tree never exceeds the
> max value for a lockdep subclass.
>
> The alternative to ripping out the lockdep coverage would be to deploy a
> dynamic lock key for every PCI device. Unfortunately, there is evidence
> that increasing the number of keys that lockdep needs to track to be
> per-PCI-device is prohibitively expensive for something like the
> cfg_access_lock.
>
> The main motivation for adding the annotation in the first place was to
> catch unlocked secondary bus resets, not necessarily catch lock ordering
> problems between cfg_access_lock and other locks. Solve that narrower
> problem with follow-on patches, and just due to targeted revert for now.
>
> Fixes: 7e89efc6e9e4 ("PCI: Lock upstream bridge for pci_reset_function()")
> Reported-by: Imre Deak <imre.deak@xxxxxxxxx>
> Closes: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_134186v1/shard-dg2-1/igt@device_reset@xxxxxxxxxxxxxxxxxxxxxxxx
> Cc: Jani Saarinen <jani.saarinen@xxxxxxxxx>
> Cc: Dave Jiang <dave.jiang@xxxxxxxxx>
> Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
In our ath11k test box commit 7e89efc6e9e4 was causing random kernel
crashes. I tested patches 1-3 and did not see anymore crashes so:
Tested-by: Kalle Valo <kvalo@xxxxxxxxxx>
Unfortunately I didn't realise to test patch 1 alone but I would assume
that's enough to fix the crashes. Please prioritise this patch so that
the regression in Linus' tree is fixed.
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