The arm-smmu driver is unable to allocate the blame for a page fault to
a specific device so it calls report_iommu_fault() with the dev argument
set to NULL. Normally this doesn't cause anything catastrophic but on a
system with the io_page_fault tracepoint enabled this results in a NULL
pointer deref (resulting in a fairly spectacular crash on the hardware
I'm currently working on).

Fix this by adding logic to the tracepoint to safely propagate NULL.

Fixes: f8f934c180f6 ("iommu/arm-smmu: Add support for driver IOMMU fault handlers")
Signed-off-by: Daniel Thompson <daniel@riscstar.com>
---
Changes in v2:
- Add a Fixes:. It points to the earliest point I can find where it becomes
  possible for the tracepoint to be triggered with dev set to NULL.
- Link to v1: https://lore.kernel.org/r/20260116-iommu-io_page_fault_null_fix-v1-1-6c20c2e62987@riscstar.com
---
 include/trace/events/iommu.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/trace/events/iommu.h b/include/trace/events/iommu.h
index 373007e567cb827458a729b8200bbcc1b7d76912..1315193f13b8812ad4e29e6b0c0c66ca806ce08d 100644
--- a/include/trace/events/iommu.h
+++ b/include/trace/events/iommu.h
@@ -131,8 +131,8 @@ DECLARE_EVENT_CLASS(iommu_error,
 	TP_ARGS(dev, iova, flags),
 
 	TP_STRUCT__entry(
-		__string(device, dev_name(dev))
-		__string(driver, dev_driver_string(dev))
+		__string(device, dev ? dev_name(dev) : NULL)
+		__string(driver, dev ? dev_driver_string(dev) : NULL)
 		__field(u64, iova)
 		__field(int, flags)
 	),

---
base-commit: 0f61b1860cc3f52aef9036d7235ed1f017632193
change-id: 20260116-iommu-io_page_fault_null_fix-f81b4e8b5423

Best regards,
-- 
Daniel Thompson <daniel@riscstar.com>

Note, event changes go through the maintainer's tree where the events are
used.

But from a tracing POV:

Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>

-- Steve


On Wed, 28 Jan 2026 15:48:01 +0000
Daniel Thompson <daniel@riscstar.com> wrote:

> The arm-smmu driver is unable to allocate the blame for a page fault to
> a specific device so it calls report_iommu_fault() with the dev argument
> set to NULL. Normally this doesn't cause anything catastrophic but on a
> system with the io_page_fault tracepoint enabled this results in a NULL
> pointer deref (resulting in a fairly spectacular crash on the hardware
> I'm currently working on).
> 
> Fix this by adding logic to the tracepoint to safely propagate NULL.
> 
> Fixes: f8f934c180f6 ("iommu/arm-smmu: Add support for driver IOMMU fault handlers")
> Signed-off-by: Daniel Thompson <daniel@riscstar.com>
> ---
> Changes in v2:
> - Add a Fixes:. It points to the earliest point I can find where it becomes
>   possible for the tracepoint to be triggered with dev set to NULL.
> - Link to v1: https://lore.kernel.org/r/20260116-iommu-io_page_fault_null_fix-v1-1-6c20c2e62987@riscstar.com
> ---
>  include/trace/events/iommu.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/include/trace/events/iommu.h b/include/trace/events/iommu.h
> index 373007e567cb827458a729b8200bbcc1b7d76912..1315193f13b8812ad4e29e6b0c0c66ca806ce08d 100644
> --- a/include/trace/events/iommu.h
> +++ b/include/trace/events/iommu.h
> @@ -131,8 +131,8 @@ DECLARE_EVENT_CLASS(iommu_error,
>  	TP_ARGS(dev, iova, flags),
>  
>  	TP_STRUCT__entry(
> -		__string(device, dev_name(dev))
> -		__string(driver, dev_driver_string(dev))
> +		__string(device, dev ? dev_name(dev) : NULL)
> +		__string(driver, dev ? dev_driver_string(dev) : NULL)
>  		__field(u64, iova)
>  		__field(int, flags)
>  	),
> 
> ---
> base-commit: 0f61b1860cc3f52aef9036d7235ed1f017632193
> change-id: 20260116-iommu-io_page_fault_null_fix-f81b4e8b5423
> 
> Best regards,