Subject: [PATCH V13 2/7] dma-resv: Fix undefined symbol when CONFIG_DMA_SHARED_BUFFER is disabled

From: "Mukesh Kumar Chaurasiya (IBM)" <[email-masked]>
Date: Fri, 24 Apr 2026 11:17:37 +0530

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 making the function declaration conditional on both
CONFIG_DEBUG_MUTEXES and CONFIG_DMA_SHARED_BUFFER. When either is
disabled, use a static inline stub instead.

Fixes: 0c6b522abc2a ("dma-buf: cleanup dma-resv shared fence debugging a bit v2")
Signed-off-by: Mukesh Kumar Chaurasiya (IBM) <[email-masked]>
---
 include/linux/dma-resv.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/dma-resv.h b/include/linux/dma-resv.h
index c5ab6fd9ebe8..23c8db0b5214 100644
--- a/include/linux/dma-resv.h
+++ b/include/linux/dma-resv.h
@@ -311,7 +311,7 @@ static inline bool dma_resv_iter_is_restarted(struct dma_resv_iter *cursor)
 #define dma_resv_held(obj) lockdep_is_held(&(obj)->lock.base)
 #define dma_resv_assert_held(obj) lockdep_assert_held(&(obj)->lock.base)
 
-#ifdef CONFIG_DEBUG_MUTEXES
+#if IS_ENABLED(CONFIG_DEBUG_MUTEXES) && IS_ENABLED(CONFIG_DMA_SHARED_BUFFER)
 void dma_resv_reset_max_fences(struct dma_resv *obj);
 #else
 static inline void dma_resv_reset_max_fences(struct dma_resv *obj) {}
-- 
2.53.0