Re: [PATCH V13 2/7] dma-resv: Fix undefined symbol when CONFIG_DMA_SHARED_BUFFER is disabled - Linaro-mm-sig

24 Apr 2026

On 4/24/26 10:34, Mukesh Kumar Chaurasiya wrote:
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On Fri, Apr 24, 2026 at 10:25:25AM +0200, Christian König wrote:
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On 4/24/26 10:06, Mukesh Kumar Chaurasiya wrote:
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On Fri, Apr 24, 2026 at 09:56:16AM +0200, Christian König wrote:
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On 4/24/26 07:47, Mukesh Kumar Chaurasiya (IBM) wrote:
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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
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>> referenced by helpers.c
>>               rust/helpers/helpers.o:(rust_helper_dma_resv_unlock)
The issue occurs because:

CONFIG_DEBUG_MUTEXES=y is enabled
CONFIG_DMA_SHARED_BUFFER is not enabled
dma_resv_reset_max_fences() is declared in the header when
CONFIG_DEBUG_MUTEXES is set
But the function is only compiled in drivers/dma-buf/dma-resv.c,
which is only built when CONFIG_DMA_SHARED_BUFFER is enabled
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.
Well we are clearly missing something here, but of hand that doesn't looks like the right fix.
When CONFIG_DMA_SHARED_BUFFER isn't enabled then the whole dma-resv.h header can't be used at all.
So you also can't call dma_resv_unlock() from the Rust helpers. Which means that we need to make the Rust helpers somehow depend on CONFIG_DMA_SHARED_BUFFER.
Alternative would be to provide dummies for the functions in dma-resv.h when CONFIG_DMA_SHARED_BUFFER isn't set, but that looks a bit like it just hides the issue.
Regards,
Christian.
What about something like this:

diff --git a/rust/helpers/dma-resv.c b/rust/helpers/dma-resv.c
index 71914d8241e2..53c119f1b144 100644
--- a/rust/helpers/dma-resv.c
+++ b/rust/helpers/dma-resv.c
@@ -2,6 +2,7 @@
#include <linux/dma-resv.h>
+#ifdef CONFIG_DMA_SHARED_BUFFER
 __rust_helper
 int rust_helper_dma_resv_lock(struct dma_resv *obj, struct ww_acquire_ctx *ctx)
 {
@@ -12,3 +13,4 @@ __rust_helper void rust_helper_dma_resv_unlock(struct dma_resv *obj)
 {
        dma_resv_unlock(obj);
 }
+#endif
This seems to fix the issue and makes sense, whoever wants to use the
dma shared buffer will anyway enable the config
Yeah that directions makes sense.
I would maybe go a step further and don't even compile rust/helpers/dma-resv.c when CONFIG_DMA_SHARED_BUFFER isn't set.
This makes sense.
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But if that is not possible for some reason then this solution is perfectly fine with me as well.
The general goal is to make the error messages when you haven't set CONFIG_DMA_SHARED_BUFFER and still try to use the DMA-buf functions easy to understand and not something cryptic.
Thanks,
Christian.
What about this one?
diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
index 625921e27dfb..09ee5cac600d 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -57,7 +57,9 @@
 #include "cred.c"
 #include "device.c"
 #include "dma.c"
+#ifdef CONFIG_DMA_SHARED_BUFFER
 #include "dma-resv.c"
+#endif
 #include "drm.c"
 #include "err.c"
 #include "irq.c"
Looks good, feel free to add Reviewed-by: Christian König christian.koenig@amd.com
But somebody more familiar with the Rust helpers should take another look on it.
Regards,
Christian.
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Regards,
Mukesh
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Regards,
Mukesh
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Fixes: 0c6b522abc2a ("dma-buf: cleanup dma-resv shared fence debugging a bit v2")
Signed-off-by: Mukesh Kumar Chaurasiya (IBM) mkchauras@gmail.com

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

    