From: Chris Wilson chris@chris-wilson.co.uk
[ Upstream commit 03e4e0a9e02cf703da331ff6cfd57d0be9bf5692 ]
Ages ago Rob Clark noted,
"Currently with fence-array, we have a potential deadlock situation. If we fence_add_callback() on an array-fence, the array-fence's lock is acquired first, and in it's ->enable_signaling() callback, it will install cbs on it's array-member fences, so the array-member's lock is acquired second.
But in the signal path, the array-member's lock is acquired first, and the array-fence's lock acquired second."
Rob proposed either extensive changes to dma-fence to unnest the fence-array signaling, or to defer the signaling onto a workqueue. This is a more refined version of the later, that should keep the latency of the fence signaling to a minimum by using an irq-work, which is executed asap.
Reported-by: Rob Clark robdclark@gmail.com Suggested-by: Rob Clark robdclark@gmail.com References: 1476635975-21981-1-git-send-email-robdclark@gmail.com Signed-off-by: Chris Wilson chris@chris-wilson.co.uk Cc: Rob Clark robdclark@gmail.com Cc: Gustavo Padovan gustavo.padovan@collabora.co.uk Cc: Sumit Semwal sumit.semwal@linaro.org Cc: Christian König christian.koenig@amd.com Reviewed-by: Christian König christian.koenig@amd.com Signed-off-by: Sumit Semwal sumit.semwal@linaro.org Link: https://patchwork.freedesktop.org/patch/msgid/20171114162719.30958-1-chris@c... Signed-off-by: Sasha Levin alexander.levin@microsoft.com --- drivers/base/Kconfig | 1 + drivers/dma-buf/dma-fence-array.c | 14 ++++++++++++-- include/linux/dma-fence-array.h | 3 +++ 3 files changed, 16 insertions(+), 2 deletions(-)
diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig index 2415ad9f6dd4..49fd50fccd48 100644 --- a/drivers/base/Kconfig +++ b/drivers/base/Kconfig @@ -249,6 +249,7 @@ config DMA_SHARED_BUFFER bool default n select ANON_INODES + select IRQ_WORK help This option enables the framework for buffer-sharing between multiple drivers. A buffer is associated with a file using driver diff --git a/drivers/dma-buf/dma-fence-array.c b/drivers/dma-buf/dma-fence-array.c index 0350829ba62e..dd1edfb27b61 100644 --- a/drivers/dma-buf/dma-fence-array.c +++ b/drivers/dma-buf/dma-fence-array.c @@ -31,6 +31,14 @@ static const char *dma_fence_array_get_timeline_name(struct dma_fence *fence) return "unbound"; }
+static void irq_dma_fence_array_work(struct irq_work *wrk) +{ + struct dma_fence_array *array = container_of(wrk, typeof(*array), work); + + dma_fence_signal(&array->base); + dma_fence_put(&array->base); +} + static void dma_fence_array_cb_func(struct dma_fence *f, struct dma_fence_cb *cb) { @@ -39,8 +47,9 @@ static void dma_fence_array_cb_func(struct dma_fence *f, struct dma_fence_array *array = array_cb->array;
if (atomic_dec_and_test(&array->num_pending)) - dma_fence_signal(&array->base); - dma_fence_put(&array->base); + irq_work_queue(&array->work); + else + dma_fence_put(&array->base); }
static bool dma_fence_array_enable_signaling(struct dma_fence *fence) @@ -136,6 +145,7 @@ struct dma_fence_array *dma_fence_array_create(int num_fences, spin_lock_init(&array->lock); dma_fence_init(&array->base, &dma_fence_array_ops, &array->lock, context, seqno); + init_irq_work(&array->work, irq_dma_fence_array_work);
array->num_fences = num_fences; atomic_set(&array->num_pending, signal_on_any ? 1 : num_fences); diff --git a/include/linux/dma-fence-array.h b/include/linux/dma-fence-array.h index 332a5420243c..bc8940ca280d 100644 --- a/include/linux/dma-fence-array.h +++ b/include/linux/dma-fence-array.h @@ -21,6 +21,7 @@ #define __LINUX_DMA_FENCE_ARRAY_H
#include <linux/dma-fence.h> +#include <linux/irq_work.h>
/** * struct dma_fence_array_cb - callback helper for fence array @@ -47,6 +48,8 @@ struct dma_fence_array { unsigned num_fences; atomic_t num_pending; struct dma_fence **fences; + + struct irq_work work; };
extern const struct dma_fence_ops dma_fence_array_ops;