| Message ID | 20241112121925.18464-1-christian.koenig@amd.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | dma-buf: fix dma_fence_array_signaled v3 | expand |
On 12/11/2024 12:19, Christian König wrote: > The function silently assumed that signaling was already enabled for the > dma_fence_array. This meant that without enabling signaling first we would > never see forward progress. > > Fix that by falling back to testing each individual fence when signaling > isn't enabled yet. > > v2: add the comment suggested by Boris why this is done this way > v3: fix the underflow pointed out by Tvrtko > > Signed-off-by: Christian König <christian.koenig@amd.com> > Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com> > --- > drivers/dma-buf/dma-fence-array.c | 25 ++++++++++++++++++++++++- > 1 file changed, 24 insertions(+), 1 deletion(-) > > diff --git a/drivers/dma-buf/dma-fence-array.c b/drivers/dma-buf/dma-fence-array.c > index 8a08ffde31e7..c3ffcc842c6f 100644 > --- a/drivers/dma-buf/dma-fence-array.c > +++ b/drivers/dma-buf/dma-fence-array.c > @@ -103,10 +103,33 @@ static bool dma_fence_array_enable_signaling(struct dma_fence *fence) > static bool dma_fence_array_signaled(struct dma_fence *fence) > { > struct dma_fence_array *array = to_dma_fence_array(fence); > + int num_pending; > + unsigned int i; > > - if (atomic_read(&array->num_pending) > 0) > + /* We need to read num_pending before checking the enable_signal bit > + * to avoid racing with the enable_signaling() implementation, which > + * might decrement the counter, and cause a partial check. > + * > + * The !--num_pending check is here to account for the any_signaled case > + * if we race with enable_signaling(), that means the !num_pending check > + * in the is_signalling_enabled branch might be outdated (num_pending > + * might have been decremented), but that's fine. The user will get the > + * right value when testing again later. > + */ Bonus points if you could please tweak to the same multi-line comment style as used in this file. > + num_pending = atomic_read(&array->num_pending); > + if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &array->base.flags)) { I am not sure if a memory barrier would be useful in between these two to ensure no re-ordering. Saying this because Documentation/atomic_t.txt and atomic_bitops.txt suggest both atomic_read and test_bit are un-ordered, in which case it could be better to explicitly mark the expectation. Regards, Tvrtko > + if (num_pending <= 0) > + goto signal; > return false; > + } > + > + for (i = 0; i < array->num_fences; ++i) { > + if (dma_fence_is_signaled(array->fences[i]) && !--num_pending) > + goto signal; > + } > + return false; > > +signal: > dma_fence_array_clear_pending_error(array); > return true; > }
diff --git a/drivers/dma-buf/dma-fence-array.c b/drivers/dma-buf/dma-fence-array.c index 8a08ffde31e7..c3ffcc842c6f 100644 --- a/drivers/dma-buf/dma-fence-array.c +++ b/drivers/dma-buf/dma-fence-array.c @@ -103,10 +103,33 @@ static bool dma_fence_array_enable_signaling(struct dma_fence *fence) static bool dma_fence_array_signaled(struct dma_fence *fence) { struct dma_fence_array *array = to_dma_fence_array(fence); + int num_pending; + unsigned int i; - if (atomic_read(&array->num_pending) > 0) + /* We need to read num_pending before checking the enable_signal bit + * to avoid racing with the enable_signaling() implementation, which + * might decrement the counter, and cause a partial check. + * + * The !--num_pending check is here to account for the any_signaled case + * if we race with enable_signaling(), that means the !num_pending check + * in the is_signalling_enabled branch might be outdated (num_pending + * might have been decremented), but that's fine. The user will get the + * right value when testing again later. + */ + num_pending = atomic_read(&array->num_pending); + if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &array->base.flags)) { + if (num_pending <= 0) + goto signal; return false; + } + + for (i = 0; i < array->num_fences; ++i) { + if (dma_fence_is_signaled(array->fences[i]) && !--num_pending) + goto signal; + } + return false; +signal: dma_fence_array_clear_pending_error(array); return true; }