Messages in this thread | | | Date | Wed, 17 Aug 2022 12:04:10 +0800 | Subject | Re: lockdep splat due to klist iteration from atomic context in Intel IOMMU driver | From | Baolu Lu <> |
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On 2022/8/15 21:57, Lennert Buytenhek wrote: > On Mon, Aug 15, 2022 at 06:32:24AM -0700, Bart Van Assche 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@acm.org> >>> 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. > And then to fix the 6.0-rc1 iommu/vt-d lockdep splat with > CONFIG_INTEL_IOMMU_DEBUGFS enabled, we could convert the Intel DMAR > IRQ handler to a threaded IRQ handler. We (Arista) carry the patch > below in our kernel tree, and the last two hunks of the patch do > exactly that, for the same reason (having to call > pci_get_domain_bus_and_slot() from the IRQ handler) but this is > probably too big of a change for 6.0-rc. > > > > commit 90a8e7da0facf198692a641fcfe6f89c478608e0 > Author: Lennert Buytenhek<buytenh@wantstofly.org> > Date: Wed Jul 13 15:34:30 2022 +0300 > > iommu/vt-d: Use report_iommu_fault() > > This patch makes iommu/vt-d call report_iommu_fault() when an I/O > page fault occurs, which has two effects: > > 1) It allows device drivers to register a callback to be notified > of I/O page faults, via the iommu_set_fault_handler() API. > > 2) It triggers the io_page_fault tracepoint in report_iommu_fault() > when an I/O page fault occurs. > > The latter point is the main aim of this patch, as it allows > rasdaemon-like daemons to be notified of I/O page faults, and to > possibly initiate corrective action in response.
The IOMMU subsystem already has a framework to handle I/O page faults:
commit fc36479db74e9 "iommu: Add a page fault handler"
And below series,
https://lore.kernel.org/linux-iommu/20220817012024.3251276-1-baolu.lu@linux.intel.com/
is trying to make it more generic. It seems to be more suitable for your case.
The report_iommu_fault() probably will be replaced by iommu_register_device_fault_handler() eventually. So I don't encourage its usage in the VT-d driver.
Best regards, baolu
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