Messages in this thread Patch in this message | | | Date | Tue, 6 Sep 2022 11:20:52 +0100 | Subject | Re: [PATCH v2 4/4] dma-buf: Check status of enable-signaling bit on debug | From | Tvrtko Ursulin <> |
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On 06/09/2022 09:39, Christian König wrote: > Am 05.09.22 um 18:35 schrieb Arvind Yadav: >> The core DMA-buf framework needs to enable signaling >> before the fence is signaled. The core DMA-buf framework >> can forget to enable signaling before the fence is signaled. > > This sentence is a bit confusing. I'm not a native speaker of English > either, but I suggest something like: > > "Fence signaling must be enable to make sure that the > dma_fence_is_signaled() function ever returns true." > >> To avoid this scenario on the debug kernel, check the >> DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT status bit before checking >> the signaling bit status to confirm that enable_signaling >> is enabled. > > This describes the implementation, but we should rather describe the > background of the change. The implementation should be obvious. > Something like this maybe: > > " > Since drivers and implementations sometimes mess this up enforce correct > behavior when DEBUG_WW_MUTEX_SLOWPATH is used during debugging. > > This should make any implementations bugs resulting in not signaled > fences much more obvious. > "
I think I follow the idea but am not sure coupling (well "coupling".. not really, but cross-contaminating in a way) dma-fence.c with a foreign and effectively unrelated concept of a ww mutex is the best way.
Instead, how about a dma-buf specific debug kconfig option?
Condition would then be, according to my understanding of the rules and expectations, along the lines of:
diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h index 775cdc0b4f24..147a9df2c9d0 100644 --- a/include/linux/dma-fence.h +++ b/include/linux/dma-fence.h @@ -428,6 +428,17 @@ dma_fence_is_signaled_locked(struct dma_fence *fence) static inline bool dma_fence_is_signaled(struct dma_fence *fence) { +#ifdef CONFIG_DEBUG_DMAFENCE + /* + * Implementations not providing the enable_signaling callback are + * required to always have signaling enabled or fences are not + * guaranteed to ever signal. + */ + if (!fence->ops->enable_signaling && + !test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &fence->flags)) + return false; +#endif + if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) return true;
Thoughts? Regards,
Tvrtko
> >> >> Signed-off-by: Arvind Yadav <Arvind.Yadav@amd.com> > > With the improved commit message this patch is Reviewed-by: Christian > König <christian.koenig@amd.com> > > Regards, > Christian. > >> --- >> >> Changes in v1 : >> 1- Addressing Christian's comment to replace >> CONFIG_DEBUG_WW_MUTEX_SLOWPATH instead of CONFIG_DEBUG_FS. >> 2- As per Christian's comment moving this patch at last so >> The version of this patch is also changed and previously >> it was [PATCH 1/4] >> >> >> --- >> include/linux/dma-fence.h | 5 +++++ >> 1 file changed, 5 insertions(+) >> >> diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h >> index 775cdc0b4f24..ba1ddc14c5d4 100644 >> --- a/include/linux/dma-fence.h >> +++ b/include/linux/dma-fence.h >> @@ -428,6 +428,11 @@ dma_fence_is_signaled_locked(struct dma_fence >> *fence) >> static inline bool >> dma_fence_is_signaled(struct dma_fence *fence) >> { >> +#ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH >> + if (!test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &fence->flags)) >> + return false; >> +#endif >> + >> if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) >> return true; >
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