On 4/24/26 10:34, Mukesh Kumar Chaurasiya wrote: > On Fri, Apr 24, 2026 at 10:25:25AM +0200, Christian König wrote: >> On 4/24/26 10:06, Mukesh Kumar Chaurasiya wrote: >>> [Sie erhalten nicht häufig E-Mails von [email protected]. Weitere >>> Informationen, warum dies wichtig ist, finden Sie unter >>> https://aka.ms/LearnAboutSenderIdentification ] >>> >>> On Fri, Apr 24, 2026 at 09:56:16AM +0200, Christian König wrote: >>>> On 4/24/26 07:47, Mukesh Kumar Chaurasiya (IBM) wrote: >>>>> 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. >>>> >>>> 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. >> 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 <[email protected]> But somebody more familiar with the Rust helpers should take another look on it. Regards, Christian. > > Regards, > Mukesh > >>> >>> Regards, >>> Mukesh >>>>> >>>>> Fixes: 0c6b522abc2a ("dma-buf: cleanup dma-resv shared fence debugging a >>>>> bit v2") >>>>> Signed-off-by: Mukesh Kumar Chaurasiya (IBM) <[email protected]> >>>>> --- >>>>> 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 >>>>> >>>> >>
