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 --- rust/helpers/dma-resv.c | 4 ++++ 1 file changed, 4 insertions(+)

diff --git a/rust/helpers/dma-resv.c b/rust/helpers/dma-resv.c index 71914d8241e2..1698092b9317 100644 --- a/rust/helpers/dma-resv.c +++ b/rust/helpers/dma-resv.c @@ -1,5 +1,7 @@ // SPDX-License-Identifier: GPL-2.0

+#ifdef CONFIG_DMA_SHARED_BUFFER + #include <linux/dma-resv.h>

__rust_helper @@ -12,3 +14,5 @@ __rust_helper void rust_helper_dma_resv_unlock(struct dma_resv *obj) { dma_resv_unlock(obj); } + +#endif

--- base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482 change-id: 20260708-dma-shared-buffer-config-bb135fdb61f4

Best regards, -- Andreas Hindborg a.hindborg@kernel.org