Re: [PATCH V17 2/7] dma-resv: Fix undefined symbol when CONFIG_DMA_SHARED_BUFFER is disabled

[Miguel Ojeda]

On Wed, Jul 8, 2026 at 10:25 AM Mukesh Kumar Chaurasiya (IBM)
<mkchauras@xxxxxxxxx> wrote:
>
> When building with LLVM=1 for architectures like powerpc where
> CONFIG_DMA_SHARED_BUFFER is not enabled, the build fails with:
>
>   ld.lld: error: undefined symbol: dma_resv_reset_max_fences
>   >>> referenced by helpers.c
>   >>>               rust/helpers/helpers.o:(rust_helper_dma_resv_unlock)
>
> The issue occurs because:
> 1. CONFIG_DEBUG_MUTEXES=y is enabled
> 2. CONFIG_DMA_SHARED_BUFFER is not enabled
> 3. dma_resv_reset_max_fences() is declared in the header when
>    CONFIG_DEBUG_MUTEXES is set
> 4. But the function is only compiled in drivers/dma-buf/dma-resv.c,
>    which is only built when CONFIG_DMA_SHARED_BUFFER is enabled
> 5. Rust helpers call dma_resv_unlock() which calls
>    dma_resv_reset_max_fences(), causing an undefined symbol
>
> Fix this by compiling `dma-resv.c` file only when CONFIG_DMA_SHARED_BUFFER
> is enabled.
>
> Fixes: 9b836641d3bf ("rust: helpers: Add bindings/wrappers for dma_resv_lock")
> Reviewed-by: Christian König <christian.koenig@xxxxxxx>
> Reviewed-by: Gary Guo <gary@xxxxxxxxxxx>
> Signed-off-by: Mukesh Kumar Chaurasiya (IBM) <mkchauras@xxxxxxxxx>

Andreas sent a similar one to:

  https://lore.kernel.org/rust-for-linux/20260708-dma-shared-buffer-config-v1-1-8c1571000855@xxxxxxxxxx/

This is earlier, but please see his approach & Sashiko's note.

Backlinking here for reference.

Cheers,
Miguel