[PATCH] io_uring/rsrc: fix build without DMA_SHARED_BUFFER

[Sasha Levin]

io_register_dmabuf_desc() calls io_register_dmabuf() unconditionally, but
io_uring/dma-buf.o is only built with CONFIG_DMA_SHARED_BUFFER enabled.
This causes an undefined reference to io_register_dmabuf() when linking
kernels with CONFIG_IO_URING=y and CONFIG_DMA_SHARED_BUFFER=n, as reported
by KernelCI for i386 allnoconfig and ARC haps_hs_smp_defconfig builds.

Move the configuration check from io_register_dmabuf() to
io_register_dmabuf_desc(), before allocating the resource node and mapped
buffer. This lets the compiler eliminate the call when DMA-BUF support
is disabled and rejects DMA-BUF registration with -EOPNOTSUPP. The check
in io_register_dmabuf() cannot handle this configuration because its
object file is not built.

Fixes: 4bb797852328 ("io_uring/rsrc: add dmabuf backed registered buffers")
Reported-by: kernelci.org bot <bot@xxxxxxxxxxxx>
Closes: https://d.kernelci.org/i/maestro:0c0fb2ae8f67a98485b9c0cd122f4e5d5156c481
Closes: https://d.kernelci.org/i/maestro:c4ceb57bdf62b29a8c2fdc83e22c1d5594f06460
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 io_uring/dma-buf.c | 2 --
 io_uring/rsrc.c    | 3 +++
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/io_uring/dma-buf.c b/io_uring/dma-buf.c
index f40c9d87ed8aa..04dd41bf53be0 100644
--- a/io_uring/dma-buf.c
+++ b/io_uring/dma-buf.c
@@ -18,8 +18,6 @@ int io_register_dmabuf(struct io_ring_ctx *ctx,
 	struct dma_buf *dmabuf = NULL;
 	int ret;
 
-	if (!IS_ENABLED(CONFIG_DMA_SHARED_BUFFER))
-		return -EOPNOTSUPP;
 	if (ctx->flags & IORING_SETUP_IOPOLL)
 		return -EOPNOTSUPP;
 	if (desc->uaddr || desc->size)
diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
index d6f7cbf731eb2..00f5ed6051e0b 100644
--- a/io_uring/rsrc.c
+++ b/io_uring/rsrc.c
@@ -907,6 +907,9 @@ static struct io_rsrc_node *io_register_dmabuf_desc(struct io_ring_ctx *ctx,
 	struct io_mapped_ubuf *imu = NULL;
 	int ret;
 
+	if (!IS_ENABLED(CONFIG_DMA_SHARED_BUFFER))
+		return ERR_PTR(-EOPNOTSUPP);
+
 	node = io_rsrc_node_alloc(ctx, IORING_RSRC_BUFFER);
 	if (!node)
 		return ERR_PTR(-ENOMEM);