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@xxxxxxx>
With the improved commit message this patch is Reviewed-by: Christian
König <christian.koenig@xxxxxxx>
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;
