Am 14.11.2017 um 17:27 schrieb Chris Wilson:
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
BTW: I've looked into this a bit as well to fix lock inversion with the
GPU scheduler. Long story short: It would be really nice to have, but a
pain to fix.
, 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@xxxxxxxxx>
Suggested-by: Rob Clark <robdclark@xxxxxxxxx>
References: 1476635975-21981-1-git-send-email-robdclark@xxxxxxxxx
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Christian König <christian.koenig@xxxxxxx>
Cc: Rob Clark <robdclark@xxxxxxxxx>
Cc: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxxxx>
Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
Cc: Christian König <christian.koenig@xxxxxxx>
---
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 2f6614c9a229..2c3cab066871 100644
--- a/drivers/base/Kconfig
+++ b/drivers/base/Kconfig
@@ -245,6 +245,7 @@ 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;
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