Re: [PATCH] amba: Fix driver_managed_dma check

[Ketan Kishore]

On 4/25/2025 7:09 PM, Robin Murphy wrote:
> Since it's not currently safe to take device_lock() in the IOMMU probe
> path, that can race against really_probe() setting dev->driver before
> attempting to bind. The race itself isn't so bad, since we're only
> concerned with dereferencing dev->driver itself anyway, but sadly my
> attempt to implement the check with minimal churn leads to a kind of
> TOCTOU issue, where dev->driver becomes valid after to_amba_driver(NULL)
> is already computed, and thus the check fails to work as intended.
>
> Will and I both hit this with the platform bus, but the pattern here is
> the same, so fix it for correctness too.
>
> Reported-by: Will McVicker <willmcvicker@xxxxxxxxxx>
> Fixes: bcb81ac6ae3c ("iommu: Get DT/ACPI parsing into the proper probe path")
> Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>
			arch_teardown_dma_ops(dev);

Hello Robin

We faced this issue with amba_dma_configure race internally as well:
Call trace:
  amba_dma_configure
  __iommu_probe_device
  probe_iommu_group
  bus_for_each_dev
  iommu_device_register
  arm_smmu_device_probe
  platform_probe
  really_probe
  __driver_probe_device
  driver_probe_device
  __device_attach_driver
  bus_for_each_drv
  __device_attach
  device_initial_probe
  bus_probe_device
  deferred_probe_work_func
  process_scheduled_works
  worker_thread
  kthread
  ret_from_fork

We raised change for this based on already merged changes that fixed the 
same TOCTOU race for the platform bus in
commit 95deee37a123 ("platform: Fix race condition during DMA
configure at IOMMU probe time") and for fsl-mc in commit 152f33ee30ee
("bus: fsl_mc: Fix driver_managed_dma check").
Link: 
https://lore.kernel.org/all/20260825-iommu_races-v2-1-49de6de71357@xxxxxxxxxxxxxxxx/

We later found this change you raised which was never merged.
Can you please help to revive and take this change forward for merge.

Reviewed-by: Ketan Kishore <ketan.kishore@xxxxxxxxxxxxxxxx>

Regards
Ketan