Re: [PATCH 1/1] iommu/vt-d: Fix lockdep splat due to klist iteration in atomic context

[Baolu Lu]

On 2022/8/19 09:59, Lu Baolu wrote:
> With CONFIG_INTEL_IOMMU_DEBUGFS enabled, below lockdep splat are seen
> when an I/O fault occurs on a machine with an Intel IOMMU in it.
>
>   DMAR: DRHD: handling fault status reg 3
>   DMAR: [DMA Write NO_PASID] Request device [00:1a.0] fault addr 0x0
>         [fault reason 0x05] PTE Write access is not set
>   DMAR: Dump dmar0 table entries for IOVA 0x0
>   DMAR: root entry: 0x0000000127f42001
>   DMAR: context entry: hi 0x0000000000001502, low 0x000000012d8ab001
>   ================================
>   WARNING: inconsistent lock state
>   5.20.0-0.rc0.20220812git7ebfc85e2cd7.10.fc38.x86_64 #1 Not tainted
>   --------------------------------
>   inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage.
>   rngd/1006 [HC1[1]:SC0[0]:HE0:SE1] takes:
>   ff177021416f2d78 (&k->k_lock){?.+.}-{2:2}, at: klist_next+0x1b/0x160
>   {HARDIRQ-ON-W} state was registered at:
>     lock_acquire+0xce/0x2d0
>     _raw_spin_lock+0x33/0x80
>     klist_add_tail+0x46/0x80
>     bus_add_device+0xee/0x150
>     device_add+0x39d/0x9a0
>     add_memory_block+0x108/0x1d0
>     memory_dev_init+0xe1/0x117
>     driver_init+0x43/0x4d
>     kernel_init_freeable+0x1c2/0x2cc
>     kernel_init+0x16/0x140
>     ret_from_fork+0x1f/0x30
>   irq event stamp: 7812
>   hardirqs last  enabled at (7811): [<ffffffff85000e86>] asm_sysvec_apic_timer_interrupt+0x16/0x20
>   hardirqs last disabled at (7812): [<ffffffff84f16894>] irqentry_enter+0x54/0x60
>   softirqs last  enabled at (7794): [<ffffffff840ff669>] __irq_exit_rcu+0xf9/0x170
>   softirqs last disabled at (7787): [<ffffffff840ff669>] __irq_exit_rcu+0xf9/0x170
>
> 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, where
> pci_get_domain_bus_and_slot() calls into bus_find_device() which iterates
> over klists.
>
> As currently there's no plan to fix the klist to make it safe to use in
> atomic context, this fixes the lockdep splat by avoid calling
> pci_get_domain_bus_and_slot() in the hardirq context.
>
> Fixes: 8ac0b64b9735 ("iommu/vt-d: Use pci_get_domain_bus_and_slot() in pgtable_walk()")
> Reported-by: Lennert Buytenhek<buytenh@xxxxxxxxxxxxxx>
> Link:https://lore.kernel.org/linux-iommu/Yvo2dfpEh%2FWC+Wrr@xxxxxxxxxxxxxx/
> Link:https://lore.kernel.org/linux-iommu/YvyBdPwrTuHHbn5X@xxxxxxxxxxxxxx/
> Signed-off-by: Lu Baolu<baolu.lu@xxxxxxxxxxxxxxx>

This patch has been queued:

https://lore.kernel.org/linux-iommu/20220823061557.1631056-1-baolu.lu@xxxxxxxxxxxxxxx/

Best regards,
baolu