Commit f130b712 authored by Chris Wilson's avatar Chris Wilson
Browse files

drm/i915: Serialise read/write of the barrier's engine 

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().

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111397


Fixes: d8af05ff ("drm/i915: Allow sharing the idle-barrier from other kernel requests")
Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: default avatarJoonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190813200905.11369-1-chris@chris-wilson.co.uk
parent b26496ae

drivers/gpu/drm/i915/i915_active.c

+23 −5
Original line number Original line Diff line number Diff line
@@ -52,11 +52,17 @@ static inline struct llist_node *barrier_to_ll(struct active_node *node) 
	return (struct llist_node *)&node->base.link;

	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 *

static inline struct intel_engine_cs *

barrier_to_engine(struct active_node *node)

barrier_to_engine(struct active_node *node)

{

{

	GEM_BUG_ON(!is_barrier(&node->base));

	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)

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);

	__mutex_init(&ref->mutex, "i915_active", key);

}

}





static bool __active_del_barrier(struct i915_active *ref,

static bool ____active_del_barrier(struct i915_active *ref,

				 struct active_node *node)

				   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 *head = NULL, *tail = NULL;

	struct llist_node *pos, *next;

	struct llist_node *pos, *next;
@@ -280,6 +287,12 @@ static bool __active_del_barrier(struct i915_active *ref, 
	return !node;

	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,

int i915_active_ref(struct i915_active *ref,

		    u64 timeline,

		    u64 timeline,

		    struct i915_request *rq)

		    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)) {

	for (p = prev; p; p = rb_next(p)) {

		struct active_node *node =

		struct active_node *node =

			rb_entry(p, struct active_node, node);

			rb_entry(p, struct active_node, node);

		struct intel_engine_cs *engine;





		if (node->timeline > idx)

		if (node->timeline > idx)

			break;

			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

		 * the barrier before we claim it, so we have to check

		 * for success.

		 * 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;

			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)) {

	llist_for_each_safe(node, next, llist_del_all(&engine->barrier_tasks)) {

		RCU_INIT_POINTER(barrier_from_ll(node)->base.request, rq);

		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);

		list_add_tail((struct list_head *)node, &rq->active_list);

	}

	}

}

}

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