The locking order for taking two fence locks is implicitly defined in
at least two ways in the code:
1) Fence containers first and other fences next, which is defined by
the enable_signaling() callbacks of dma_fence_chain and
dma_fence_array.
2) Reverse signal order, which is used by __i915_active_fence_set().
Now 1) implies 2), except for the signal_on_any mode of dma_fence_array
and 2) does not imply 1), and also 1) makes locking order between
different containers confusing.
Establish 2) and fix up the signal_on_any mode by calling
enable_signaling() on such fences unlocked at creation.
Cc: linaro-mm-sig@xxxxxxxxxxxxxxxx
Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
Cc: Christian König <christian.koenig@xxxxxxx>
Signed-off-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
---
drivers/dma-buf/dma-fence-array.c | 13 +++--
drivers/dma-buf/dma-fence-chain.c | 3 +-
drivers/dma-buf/dma-fence.c | 79 +++++++++++++++++++++----------
include/linux/dma-fence.h | 3 ++
4 files changed, 69 insertions(+), 29 deletions(-)
diff --git a/drivers/dma-buf/dma-fence-array.c b/drivers/dma-buf/dma-fence-array.c
index 3e07f961e2f3..0322b92909fe 100644
--- a/drivers/dma-buf/dma-fence-array.c
+++ b/drivers/dma-buf/dma-fence-array.c
@@ -84,8 +84,8 @@ static bool dma_fence_array_enable_signaling(struct dma_fence *fence)
* insufficient).
*/
dma_fence_get(&array->base);
- if (dma_fence_add_callback(array->fences[i], &cb[i].cb,
- dma_fence_array_cb_func)) {
+ if (dma_fence_add_callback_nested(array->fences[i], &cb[i].cb,
+ dma_fence_array_cb_func)) {
int error = array->fences[i]->error;
dma_fence_array_set_pending_error(array, error);
@@ -158,6 +158,7 @@ struct dma_fence_array *dma_fence_array_create(int num_fences,
{
struct dma_fence_array *array;
size_t size = sizeof(*array);
+ struct dma_fence *fence;
/* Allocate the callback structures behind the array. */
size += num_fences * sizeof(struct dma_fence_array_cb);
@@ -165,8 +166,9 @@ struct dma_fence_array *dma_fence_array_create(int num_fences,
if (!array)
return NULL;
+ fence = &array->base;
spin_lock_init(&array->lock);
- dma_fence_init(&array->base, &dma_fence_array_ops, &array->lock,
+ dma_fence_init(fence, &dma_fence_array_ops, &array->lock,
context, seqno);
init_irq_work(&array->work, irq_dma_fence_array_work);
@@ -174,7 +176,10 @@ struct dma_fence_array *dma_fence_array_create(int num_fences,
atomic_set(&array->num_pending, signal_on_any ? 1 : num_fences);
array->fences = fences;
- array->base.error = PENDING_ERROR;
+ fence->error = PENDING_ERROR;
+
+ if (signal_on_any)
+ dma_fence_enable_sw_signaling(fence);
return array;
}
diff --git a/drivers/dma-buf/dma-fence-chain.c b/drivers/dma-buf/dma-fence-chain.c
index 1b4cb3e5cec9..0518e53880f6 100644
--- a/drivers/dma-buf/dma-fence-chain.c
+++ b/drivers/dma-buf/dma-fence-chain.c
@@ -152,7 +152,8 @@ static bool dma_fence_chain_enable_signaling(struct dma_fence *fence)
struct dma_fence *f = chain ? chain->fence : fence;
dma_fence_get(f);
- if (!dma_fence_add_callback(f, &head->cb, dma_fence_chain_cb)) {
+ if (!dma_fence_add_callback_nested(f, &head->cb,
+ dma_fence_chain_cb)) {
dma_fence_put(fence);
return true;
}
diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
index 066400ed8841..90a3d5121746 100644
--- a/drivers/dma-buf/dma-fence.c
+++ b/drivers/dma-buf/dma-fence.c
@@ -610,6 +610,37 @@ void dma_fence_enable_sw_signaling(struct dma_fence *fence)
}
EXPORT_SYMBOL(dma_fence_enable_sw_signaling);
+static int __dma_fence_add_callback(struct dma_fence *fence,
+ struct dma_fence_cb *cb,
+ dma_fence_func_t func,
+ int nest_level)
+{
+ unsigned long flags;
+ int ret = 0;
+
+ if (WARN_ON(!fence || !func))
+ return -EINVAL;
+
+ if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) {
+ INIT_LIST_HEAD(&cb->node);
+ return -ENOENT;
+ }
+
+ spin_lock_irqsave_nested(fence->lock, flags, 0);
+
+ if (__dma_fence_enable_signaling(fence)) {
+ cb->func = func;
+ list_add_tail(&cb->node, &fence->cb_list);
+ } else {
+ INIT_LIST_HEAD(&cb->node);
+ ret = -ENOENT;
+ }
+
+ spin_unlock_irqrestore(fence->lock, flags);
+
+ return ret;
+}
+
/**
* dma_fence_add_callback - add a callback to be called when the fence
* is signaled
@@ -635,33 +666,33 @@ EXPORT_SYMBOL(dma_fence_enable_sw_signaling);
int dma_fence_add_callback(struct dma_fence *fence, struct dma_fence_cb *cb,
dma_fence_func_t func)
{
- unsigned long flags;
- int ret = 0;
-
- if (WARN_ON(!fence || !func))
- return -EINVAL;
-
- if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) {
- INIT_LIST_HEAD(&cb->node);
- return -ENOENT;
- }
-
- spin_lock_irqsave(fence->lock, flags);
-
- if (__dma_fence_enable_signaling(fence)) {
- cb->func = func;
- list_add_tail(&cb->node, &fence->cb_list);
- } else {
- INIT_LIST_HEAD(&cb->node);
- ret = -ENOENT;
- }
-
- spin_unlock_irqrestore(fence->lock, flags);
-
- return ret;
+ return __dma_fence_add_callback(fence, cb, func, 0);
}
EXPORT_SYMBOL(dma_fence_add_callback);
+/**
+ * dma_fence_add_callback_nested - add a callback from within a fence locked
+ * section to be called when the fence is signaled
+ * @fence: the fence to wait on
+ * @cb: the callback to register
+ * @func: the function to call
+ *
+ * This function is identical to dma_fence_add_callback() except it is
+ * intended to be used from within a section where the fence lock of
+ * another fence might be locked, and where it is guaranteed that
+ * other fence will signal _after_ @fence.
+ *
+ * Returns 0 in case of success, -ENOENT if the fence is already signaled
+ * and -EINVAL in case of error.
+ */
+int dma_fence_add_callback_nested(struct dma_fence *fence,
+ struct dma_fence_cb *cb,
+ dma_fence_func_t func)
+{
+ return __dma_fence_add_callback(fence, cb, func, SINGLE_DEPTH_NESTING);
+}
+EXPORT_SYMBOL(dma_fence_add_callback_nested);
+
/**
* dma_fence_get_status - returns the status upon completion
* @fence: the dma_fence to query
diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
index 1ea691753bd3..405cd83936f6 100644
--- a/include/linux/dma-fence.h
+++ b/include/linux/dma-fence.h
@@ -377,6 +377,9 @@ signed long dma_fence_default_wait(struct dma_fence *fence,
int dma_fence_add_callback(struct dma_fence *fence,
struct dma_fence_cb *cb,
dma_fence_func_t func);
+int dma_fence_add_callback_nested(struct dma_fence *fence,
+ struct dma_fence_cb *cb,
+ dma_fence_func_t func);
bool dma_fence_remove_callback(struct dma_fence *fence,
struct dma_fence_cb *cb);
void dma_fence_enable_sw_signaling(struct dma_fence *fence);
--
2.31.1
