Re: lockdep splat due to klist iteration from atomic context in Intel IOMMU driver

[Baolu Lu]

On 2022/8/15 21:32, Bart Van Assche wrote:
> On 8/15/22 05:05, Lennert Buytenhek wrote:
> > On a build of 7ebfc85e2cd7 ("Merge tag 'net-6.0-rc1' of
> > git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net"), with
> > CONFIG_INTEL_IOMMU_DEBUGFS enabled, I am seeing the lockdep splat
> > below when an I/O page fault occurs on a machine with an Intel
> > IOMMU in it.
> >
> > The issue seems to be the klist iterator functions using
> > spin_*lock_irq*() but the klist insertion functions using
> > spin_*lock(), combined with the Intel DMAR IOMMU driver iterating
> > over klists from atomic (hardirq) context as of commit 8ac0b64b9735
> > ("iommu/vt-d: Use pci_get_domain_bus_and_slot() in pgtable_walk()")
> > when CONFIG_INTEL_IOMMU_DEBUGFS is enabled, where
> > pci_get_domain_bus_and_slot() calls into bus_find_device() which
> > iterates over klists.
> >
> > I found this commit from 2018:
> >
> >     commit 624fa7790f80575a4ec28fbdb2034097dc18d051
> >     Author: Bart Van Assche <bvanassche@xxxxxxx>
> >     Date:   Fri Jun 22 14:54:49 2018 -0700
> >
> >         scsi: klist: Make it safe to use klists in atomic context
> >
> > This commit switched lib/klist.c:klist_{prev,next} from
> > spin_{,un}lock() to spin_{lock_irqsave,unlock_irqrestore}(), but left
> > the spin_{,un}lock() calls in add_{head,tail}() untouched.
> >
> > The simplest fix for this would be to switch 
> > lib/klist.c:add_{head,tail}()
> > over to use the IRQ-safe spinlock variants as well?
>
> Another possibility would be to evaluate whether it is safe to revert 
> commit 624fa7790f80 ("scsi: klist: Make it safe to use klists in atomic 
> context"). That commit is no longer needed by the SRP transport driver 
> since the legacy block layer has been removed from the kernel.

If so, pci_get_domain_bus_and_slot() can not be used in this interrupt
context, right?

Best regards,
baolu