Re: [PATCH] iommu/vt-d: Remove unnecessary locking in intel_irq_remapping_alloc()

[Robin Murphy]

On 2023-04-27 04:37, Nicolin Chen wrote:
> On Thu, Apr 27, 2023 at 11:20:40AM +0800, Baolu Lu wrote:
>
> > > Attaching WARNINGs:
> > > [   19.680725] ------------[ cut here ]------------
> > > [   19.681083] WARNING: CPU: 0 PID: 561 at include/linux/mmap_lock.h:161 track_pfn_remap+0xf5/0x100
>
> > > [   19.684817] Call Trace:
> > > [   19.684893]  <TASK>
> > > [   19.684967]  remap_pfn_range+0x3e/0xa0
> > > [   19.685084]  vfio_pci_mmap_fault+0x8a/0x160 [vfio_pci_core]
>   
> > I took a quick look. It seems that above warnings are irrelevant to this
> > commit. Can you please simply revert this commit and check whether there
> > are any changes?
>
> I tried on top of the v6.3-rc5 tag. The warnings were triggered
> constantly. And reverting the commit fixes it:
> nicolinc@Asurada-Nvidia:~/work/mkt/images/nicolinc/src/kernel$ git log --oneline -2
> cb3dc9b2417e (HEAD -> v6.3-rc5) Revert "iommu/vt-d: Remove unnecessary locking in intel_irq_remapping_alloc()"
> 7e364e56293b (tag: v6.3-rc5, jgg/linus) Linux 6.3-rc5
>
> I don't think the commit is the causation yet there seems to be
> a strong correlation here...

The correlation is probably that you're now getting to see a genuine 
warning from lockdep_assert_held(), since intel-iommu is no longer 
causing debug_locks to be turned off earlier.

Robin.