Re: [RFC PATCH v1 1/2] dma-buf: keep DMABUF_DEBUG off by default

[Bryan O'Donoghue <bod@kernel.org>]

On 23/09/2026 08:42, Jianfeng Liu wrote:
> Commit 143755bdabaa9 ("dma-buf: Make DMABUF_DEBUG default to y on
> DEBUG_KERNEL kernels") fixed a dangling reference in the DMABUF_DEBUG
> default, which had the side effect of enabling the option (and with it
> the page-stripping sg_table wrapper handed to importers) on every
> kernel with DEBUG_KERNEL=y - i.e. virtually every distro kernel.
> 
> drm/msm is broken by this: it maps imported dma-bufs into the GPU's
> own pagetables with iommu_map_sgtable(), which needs the struct page
> of the attachment sg_table, and it fills the GEM object's page array
> through drm_prime_sg_to_page_array().  With the debug wrapper in
> place both silently produce garbage (the wrapper zeroes sg->length,
> so the page iterator yields nothing and an uninitialized array is
> kept).  The VM_BIND map job then fails asynchronously after userspace
> has already enqueued GPU work referencing the mapping, which shows up
> as an arm-smmu translation fault from UCHE, e.g.:
> 
>    gpu fault: ttbr0=000000088a889000 iova=000000010741c000 dir=READ
>    type=TRANSLATION source=UCHE
> 
> This breaks hardware video decode (clapper, chromium) on Adreno
> systems; bisected on a Snapdragon laptop as v7.3-rc3 good,
> v7.3-rc4 bad, culprit 143755bdabaa9.
> 
> Revert the default until importers that legitimately need to build
> phys-based mappings have been converted.
> 
> Fixes: 143755bdabaa9 ("dma-buf: Make DMABUF_DEBUG default to y on DEBUG_KERNEL kernels")
> Signed-off-by: Jianfeng Liu <liujianfeng1994@gmail.com>

This is a very obviously LLM generated patch.

Please state so in the commit log.

Also I don't believe reverting the change is correct. Fix the bug where 
it exists in Adreno.

---
bod