On Wed, Jul 8, 2026 at 1:53 PM Andreas Hindborg a.hindborg@kernel.org wrote:

Commit 9b836641d3bf ("rust: helpers: Add bindings/wrappers for dma_resv_lock") added rust_helper_dma_resv_lock() and rust_helper_dma_resv_unlock() unconditionally. However, the dma-resv functionality is only available when CONFIG_DMA_SHARED_BUFFER is enabled, resulting in the following link error when it is not:

  LD      .tmp_vmlinux1
ld.lld: error: undefined symbol: dma_resv_reset_max_fences
>>> referenced by dma-resv.h:463
>>>               rust/helpers/helpers.o:(rust_helper_dma_resv_unlock) in archive vmlinux.a

The dma_resv_unlock() inline in <linux/dma-resv.h> calls dma_resv_reset_max_fences(), which is only compiled into drivers/dma-buf/dma-resv.c when CONFIG_DMA_SHARED_BUFFER is set. With the option disabled the symbol is never defined, so the helper fails to link.

Fix this by guarding the helper definitions with `#ifdef CONFIG_DMA_SHARED_BUFFER`.

The only user of this helper is the DRM shmem abstractions, which already depend on `CONFIG_DMA_SHARED_BUFFER`.

Cc: stable@vger.kernel.org Fixes: 9b836641d3bf ("rust: helpers: Add bindings/wrappers for dma_resv_lock") Signed-off-by: Andreas Hindborg a.hindborg@kernel.org

Please see:

https://lore.kernel.org/rust-for-linux/20260708082454.1254320-3-mkchauras@gm...

Cheers, Miguel