We use the request pointer inside the i915_active_node as the indicator
of the barrier's status; we mark it as used during
i915_request_add_active_barriers(), and search for an available barrier
in reuse_idle_barrier(). That check must be carefully serialised to
ensure we do use an engine for the barrier and not just a random
pointer. (Along the other reuse path, we are fully serialised by the
timeline->mutex.) The acquisition of the barrier itself is ordered through
the strong memory barrier in llist_del_all().
Fixes: d8af05ff38ae ("drm/i915: Allow sharing the idle-barrier from other
kernel requests")
Signed-off-by: Chris Wilson <[email protected]>
---
drivers/gpu/drm/i915/i915_active.c | 28 +++++++++++++++++++++++-----
1 file changed, 23 insertions(+), 5 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_active.c
b/drivers/gpu/drm/i915/i915_active.c
index 7698fcaa648a..2439c4f62ad8 100644
--- a/drivers/gpu/drm/i915/i915_active.c
+++ b/drivers/gpu/drm/i915/i915_active.c
@@ -52,11 +52,17 @@ static inline struct llist_node *barrier_to_ll(struct
active_node *node)
return (struct llist_node *)&node->base.link;
}
+static inline struct intel_engine_cs *
+__barrier_to_engine(struct active_node *node)
+{
+ return (struct intel_engine_cs *)READ_ONCE(node->base.link.prev);
+}
+
static inline struct intel_engine_cs *
barrier_to_engine(struct active_node *node)
{
GEM_BUG_ON(!is_barrier(&node->base));
- return (struct intel_engine_cs *)node->base.link.prev;
+ return __barrier_to_engine(node);
}
static inline struct active_node *barrier_from_ll(struct llist_node *x)
@@ -239,10 +245,11 @@ void __i915_active_init(struct drm_i915_private *i915,
__mutex_init(&ref->mutex, "i915_active", key);
}
-static bool __active_del_barrier(struct i915_active *ref,
- struct active_node *node)
+static bool ____active_del_barrier(struct i915_active *ref,
+ struct active_node *node,
+ struct intel_engine_cs *engine)
+
{
- struct intel_engine_cs *engine = barrier_to_engine(node);
struct llist_node *head = NULL, *tail = NULL;
struct llist_node *pos, *next;
@@ -280,6 +287,12 @@ static bool __active_del_barrier(struct i915_active *ref,
return !node;
}
+static bool
+__active_del_barrier(struct i915_active *ref, struct active_node *node)
+{
+ return ____active_del_barrier(ref, node, barrier_to_engine(node));
+}
+
int i915_active_ref(struct i915_active *ref,
u64 timeline,
struct i915_request *rq)
@@ -517,6 +530,7 @@ static struct active_node *reuse_idle_barrier(struct
i915_active *ref, u64 idx)
for (p = prev; p; p = rb_next(p)) {
struct active_node *node =
rb_entry(p, struct active_node, node);
+ struct intel_engine_cs *engine;
if (node->timeline > idx)
break;
@@ -534,7 +548,10 @@ static struct active_node *reuse_idle_barrier(struct
i915_active *ref, u64 idx)
* the barrier before we claim it, so we have to check
* for success.
*/
- if (is_barrier(&node->base) && __active_del_barrier(ref, node))
+ engine = __barrier_to_engine(node);
+ smp_rmb(); /* serialise with add_active_barriers */
+ if (is_barrier(&node->base) &&
+ ____active_del_barrier(ref, node, engine))
goto match;
}
@@ -674,6 +691,7 @@ void i915_request_add_active_barriers(struct i915_request
*rq)
*/
llist_for_each_safe(node, next, llist_del_all(&engine->barrier_tasks)) {
RCU_INIT_POINTER(barrier_from_ll(node)->base.request, rq);
+ smp_wmb(); /* serialise with reuse_idle_barrier */
list_add_tail((struct list_head *)node, &rq->active_list);
}
}
--
2.23.0.rc1
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