xref: /linux/drivers/gpu/drm/i915/i915_active.c (revision 2c1ed907520c50326b8f604907a8478b27881a2e)
1 /*
2  * SPDX-License-Identifier: MIT
3  *
4  * Copyright © 2019 Intel Corporation
5  */
6 
7 #include <linux/debugobjects.h>
8 
9 #include "gt/intel_context.h"
10 #include "gt/intel_engine_heartbeat.h"
11 #include "gt/intel_engine_pm.h"
12 #include "gt/intel_ring.h"
13 
14 #include "i915_drv.h"
15 #include "i915_active.h"
16 
17 /*
18  * Active refs memory management
19  *
20  * To be more economical with memory, we reap all the i915_active trees as
21  * they idle (when we know the active requests are inactive) and allocate the
22  * nodes from a local slab cache to hopefully reduce the fragmentation.
23  */
24 static struct kmem_cache *slab_cache;
25 
26 struct active_node {
27 	struct rb_node node;
28 	struct i915_active_fence base;
29 	struct i915_active *ref;
30 	u64 timeline;
31 };
32 
33 #define fetch_node(x) rb_entry(READ_ONCE(x), typeof(struct active_node), node)
34 
35 static inline struct active_node *
node_from_active(struct i915_active_fence * active)36 node_from_active(struct i915_active_fence *active)
37 {
38 	return container_of(active, struct active_node, base);
39 }
40 
41 #define take_preallocated_barriers(x) llist_del_all(&(x)->preallocated_barriers)
42 
is_barrier(const struct i915_active_fence * active)43 static inline bool is_barrier(const struct i915_active_fence *active)
44 {
45 	return IS_ERR(rcu_access_pointer(active->fence));
46 }
47 
barrier_to_ll(struct active_node * node)48 static inline struct llist_node *barrier_to_ll(struct active_node *node)
49 {
50 	GEM_BUG_ON(!is_barrier(&node->base));
51 	return (struct llist_node *)&node->base.cb.node;
52 }
53 
54 static inline struct intel_engine_cs *
__barrier_to_engine(struct active_node * node)55 __barrier_to_engine(struct active_node *node)
56 {
57 	return (struct intel_engine_cs *)READ_ONCE(node->base.cb.node.prev);
58 }
59 
60 static inline struct intel_engine_cs *
barrier_to_engine(struct active_node * node)61 barrier_to_engine(struct active_node *node)
62 {
63 	GEM_BUG_ON(!is_barrier(&node->base));
64 	return __barrier_to_engine(node);
65 }
66 
barrier_from_ll(struct llist_node * x)67 static inline struct active_node *barrier_from_ll(struct llist_node *x)
68 {
69 	return container_of((struct list_head *)x,
70 			    struct active_node, base.cb.node);
71 }
72 
73 #if IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM) && IS_ENABLED(CONFIG_DEBUG_OBJECTS)
74 
active_debug_hint(void * addr)75 static void *active_debug_hint(void *addr)
76 {
77 	struct i915_active *ref = addr;
78 
79 	return (void *)ref->active ?: (void *)ref->retire ?: (void *)ref;
80 }
81 
82 static const struct debug_obj_descr active_debug_desc = {
83 	.name = "i915_active",
84 	.debug_hint = active_debug_hint,
85 };
86 
debug_active_init(struct i915_active * ref)87 static void debug_active_init(struct i915_active *ref)
88 {
89 	debug_object_init(ref, &active_debug_desc);
90 }
91 
debug_active_activate(struct i915_active * ref)92 static void debug_active_activate(struct i915_active *ref)
93 {
94 	lockdep_assert_held(&ref->tree_lock);
95 	debug_object_activate(ref, &active_debug_desc);
96 }
97 
debug_active_deactivate(struct i915_active * ref)98 static void debug_active_deactivate(struct i915_active *ref)
99 {
100 	lockdep_assert_held(&ref->tree_lock);
101 	if (!atomic_read(&ref->count)) /* after the last dec */
102 		debug_object_deactivate(ref, &active_debug_desc);
103 }
104 
debug_active_fini(struct i915_active * ref)105 static void debug_active_fini(struct i915_active *ref)
106 {
107 	debug_object_free(ref, &active_debug_desc);
108 }
109 
debug_active_assert(struct i915_active * ref)110 static void debug_active_assert(struct i915_active *ref)
111 {
112 	debug_object_assert_init(ref, &active_debug_desc);
113 }
114 
115 #else
116 
debug_active_init(struct i915_active * ref)117 static inline void debug_active_init(struct i915_active *ref) { }
debug_active_activate(struct i915_active * ref)118 static inline void debug_active_activate(struct i915_active *ref) { }
debug_active_deactivate(struct i915_active * ref)119 static inline void debug_active_deactivate(struct i915_active *ref) { }
debug_active_fini(struct i915_active * ref)120 static inline void debug_active_fini(struct i915_active *ref) { }
debug_active_assert(struct i915_active * ref)121 static inline void debug_active_assert(struct i915_active *ref) { }
122 
123 #endif
124 
125 static void
__active_retire(struct i915_active * ref)126 __active_retire(struct i915_active *ref)
127 {
128 	struct rb_root root = RB_ROOT;
129 	struct active_node *it, *n;
130 	unsigned long flags;
131 
132 	GEM_BUG_ON(i915_active_is_idle(ref));
133 
134 	/* return the unused nodes to our slabcache -- flushing the allocator */
135 	if (!atomic_dec_and_lock_irqsave(&ref->count, &ref->tree_lock, flags))
136 		return;
137 
138 	GEM_BUG_ON(rcu_access_pointer(ref->excl.fence));
139 	debug_active_deactivate(ref);
140 
141 	/* Even if we have not used the cache, we may still have a barrier */
142 	if (!ref->cache)
143 		ref->cache = fetch_node(ref->tree.rb_node);
144 
145 	/* Keep the MRU cached node for reuse */
146 	if (ref->cache) {
147 		/* Discard all other nodes in the tree */
148 		rb_erase(&ref->cache->node, &ref->tree);
149 		root = ref->tree;
150 
151 		/* Rebuild the tree with only the cached node */
152 		rb_link_node(&ref->cache->node, NULL, &ref->tree.rb_node);
153 		rb_insert_color(&ref->cache->node, &ref->tree);
154 		GEM_BUG_ON(ref->tree.rb_node != &ref->cache->node);
155 
156 		/* Make the cached node available for reuse with any timeline */
157 		ref->cache->timeline = 0; /* needs cmpxchg(u64) */
158 	}
159 
160 	spin_unlock_irqrestore(&ref->tree_lock, flags);
161 
162 	/* After the final retire, the entire struct may be freed */
163 	if (ref->retire)
164 		ref->retire(ref);
165 
166 	/* ... except if you wait on it, you must manage your own references! */
167 	wake_up_var(ref);
168 
169 	/* Finally free the discarded timeline tree  */
170 	rbtree_postorder_for_each_entry_safe(it, n, &root, node) {
171 		GEM_BUG_ON(i915_active_fence_isset(&it->base));
172 		kmem_cache_free(slab_cache, it);
173 	}
174 }
175 
176 static void
active_work(struct work_struct * wrk)177 active_work(struct work_struct *wrk)
178 {
179 	struct i915_active *ref = container_of(wrk, typeof(*ref), work);
180 
181 	GEM_BUG_ON(!atomic_read(&ref->count));
182 	if (atomic_add_unless(&ref->count, -1, 1))
183 		return;
184 
185 	__active_retire(ref);
186 }
187 
188 static void
active_retire(struct i915_active * ref)189 active_retire(struct i915_active *ref)
190 {
191 	GEM_BUG_ON(!atomic_read(&ref->count));
192 	if (atomic_add_unless(&ref->count, -1, 1))
193 		return;
194 
195 	if (ref->flags & I915_ACTIVE_RETIRE_SLEEPS) {
196 		queue_work(system_unbound_wq, &ref->work);
197 		return;
198 	}
199 
200 	__active_retire(ref);
201 }
202 
203 static inline struct dma_fence **
__active_fence_slot(struct i915_active_fence * active)204 __active_fence_slot(struct i915_active_fence *active)
205 {
206 	return (struct dma_fence ** __force)&active->fence;
207 }
208 
209 static inline bool
active_fence_cb(struct dma_fence * fence,struct dma_fence_cb * cb)210 active_fence_cb(struct dma_fence *fence, struct dma_fence_cb *cb)
211 {
212 	struct i915_active_fence *active =
213 		container_of(cb, typeof(*active), cb);
214 
215 	return try_cmpxchg(__active_fence_slot(active), &fence, NULL);
216 }
217 
218 static void
node_retire(struct dma_fence * fence,struct dma_fence_cb * cb)219 node_retire(struct dma_fence *fence, struct dma_fence_cb *cb)
220 {
221 	if (active_fence_cb(fence, cb))
222 		active_retire(container_of(cb, struct active_node, base.cb)->ref);
223 }
224 
225 static void
excl_retire(struct dma_fence * fence,struct dma_fence_cb * cb)226 excl_retire(struct dma_fence *fence, struct dma_fence_cb *cb)
227 {
228 	if (active_fence_cb(fence, cb))
229 		active_retire(container_of(cb, struct i915_active, excl.cb));
230 }
231 
__active_lookup(struct i915_active * ref,u64 idx)232 static struct active_node *__active_lookup(struct i915_active *ref, u64 idx)
233 {
234 	struct active_node *it;
235 
236 	GEM_BUG_ON(idx == 0); /* 0 is the unordered timeline, rsvd for cache */
237 
238 	/*
239 	 * We track the most recently used timeline to skip a rbtree search
240 	 * for the common case, under typical loads we never need the rbtree
241 	 * at all. We can reuse the last slot if it is empty, that is
242 	 * after the previous activity has been retired, or if it matches the
243 	 * current timeline.
244 	 */
245 	it = READ_ONCE(ref->cache);
246 	if (it) {
247 		u64 cached = READ_ONCE(it->timeline);
248 
249 		/* Once claimed, this slot will only belong to this idx */
250 		if (cached == idx)
251 			return it;
252 
253 		/*
254 		 * An unclaimed cache [.timeline=0] can only be claimed once.
255 		 *
256 		 * If the value is already non-zero, some other thread has
257 		 * claimed the cache and we know that is does not match our
258 		 * idx. If, and only if, the timeline is currently zero is it
259 		 * worth competing to claim it atomically for ourselves (for
260 		 * only the winner of that race will cmpxchg return the old
261 		 * value of 0).
262 		 */
263 		if (!cached && !cmpxchg64(&it->timeline, 0, idx))
264 			return it;
265 	}
266 
267 	BUILD_BUG_ON(offsetof(typeof(*it), node));
268 
269 	/* While active, the tree can only be built; not destroyed */
270 	GEM_BUG_ON(i915_active_is_idle(ref));
271 
272 	it = fetch_node(ref->tree.rb_node);
273 	while (it) {
274 		if (it->timeline < idx) {
275 			it = fetch_node(it->node.rb_right);
276 		} else if (it->timeline > idx) {
277 			it = fetch_node(it->node.rb_left);
278 		} else {
279 			WRITE_ONCE(ref->cache, it);
280 			break;
281 		}
282 	}
283 
284 	/* NB: If the tree rotated beneath us, we may miss our target. */
285 	return it;
286 }
287 
288 static struct i915_active_fence *
active_instance(struct i915_active * ref,u64 idx)289 active_instance(struct i915_active *ref, u64 idx)
290 {
291 	struct active_node *node;
292 	struct rb_node **p, *parent;
293 
294 	node = __active_lookup(ref, idx);
295 	if (likely(node))
296 		return &node->base;
297 
298 	spin_lock_irq(&ref->tree_lock);
299 	GEM_BUG_ON(i915_active_is_idle(ref));
300 
301 	parent = NULL;
302 	p = &ref->tree.rb_node;
303 	while (*p) {
304 		parent = *p;
305 
306 		node = rb_entry(parent, struct active_node, node);
307 		if (node->timeline == idx)
308 			goto out;
309 
310 		if (node->timeline < idx)
311 			p = &parent->rb_right;
312 		else
313 			p = &parent->rb_left;
314 	}
315 
316 	/*
317 	 * XXX: We should preallocate this before i915_active_ref() is ever
318 	 *  called, but we cannot call into fs_reclaim() anyway, so use GFP_ATOMIC.
319 	 */
320 	node = kmem_cache_alloc(slab_cache, GFP_ATOMIC);
321 	if (!node)
322 		goto out;
323 
324 	__i915_active_fence_init(&node->base, NULL, node_retire);
325 	node->ref = ref;
326 	node->timeline = idx;
327 
328 	rb_link_node(&node->node, parent, p);
329 	rb_insert_color(&node->node, &ref->tree);
330 
331 out:
332 	WRITE_ONCE(ref->cache, node);
333 	spin_unlock_irq(&ref->tree_lock);
334 
335 	return &node->base;
336 }
337 
__i915_active_init(struct i915_active * ref,int (* active)(struct i915_active * ref),void (* retire)(struct i915_active * ref),unsigned long flags,struct lock_class_key * mkey,struct lock_class_key * wkey)338 void __i915_active_init(struct i915_active *ref,
339 			int (*active)(struct i915_active *ref),
340 			void (*retire)(struct i915_active *ref),
341 			unsigned long flags,
342 			struct lock_class_key *mkey,
343 			struct lock_class_key *wkey)
344 {
345 	debug_active_init(ref);
346 
347 	ref->flags = flags;
348 	ref->active = active;
349 	ref->retire = retire;
350 
351 	spin_lock_init(&ref->tree_lock);
352 	ref->tree = RB_ROOT;
353 	ref->cache = NULL;
354 
355 	init_llist_head(&ref->preallocated_barriers);
356 	atomic_set(&ref->count, 0);
357 	__mutex_init(&ref->mutex, "i915_active", mkey);
358 	__i915_active_fence_init(&ref->excl, NULL, excl_retire);
359 	INIT_WORK(&ref->work, active_work);
360 #if IS_ENABLED(CONFIG_LOCKDEP)
361 	lockdep_init_map(&ref->work.lockdep_map, "i915_active.work", wkey, 0);
362 #endif
363 }
364 
____active_del_barrier(struct i915_active * ref,struct active_node * node,struct intel_engine_cs * engine)365 static bool ____active_del_barrier(struct i915_active *ref,
366 				   struct active_node *node,
367 				   struct intel_engine_cs *engine)
368 
369 {
370 	struct llist_node *head = NULL, *tail = NULL;
371 	struct llist_node *pos, *next;
372 
373 	GEM_BUG_ON(node->timeline != engine->kernel_context->timeline->fence_context);
374 
375 	/*
376 	 * Rebuild the llist excluding our node. We may perform this
377 	 * outside of the kernel_context timeline mutex and so someone
378 	 * else may be manipulating the engine->barrier_tasks, in
379 	 * which case either we or they will be upset :)
380 	 *
381 	 * A second __active_del_barrier() will report failure to claim
382 	 * the active_node and the caller will just shrug and know not to
383 	 * claim ownership of its node.
384 	 *
385 	 * A concurrent i915_request_add_active_barriers() will miss adding
386 	 * any of the tasks, but we will try again on the next -- and since
387 	 * we are actively using the barrier, we know that there will be
388 	 * at least another opportunity when we idle.
389 	 */
390 	llist_for_each_safe(pos, next, llist_del_all(&engine->barrier_tasks)) {
391 		if (node == barrier_from_ll(pos)) {
392 			node = NULL;
393 			continue;
394 		}
395 
396 		pos->next = head;
397 		head = pos;
398 		if (!tail)
399 			tail = pos;
400 	}
401 	if (head)
402 		llist_add_batch(head, tail, &engine->barrier_tasks);
403 
404 	return !node;
405 }
406 
407 static bool
__active_del_barrier(struct i915_active * ref,struct active_node * node)408 __active_del_barrier(struct i915_active *ref, struct active_node *node)
409 {
410 	return ____active_del_barrier(ref, node, barrier_to_engine(node));
411 }
412 
413 static bool
replace_barrier(struct i915_active * ref,struct i915_active_fence * active)414 replace_barrier(struct i915_active *ref, struct i915_active_fence *active)
415 {
416 	if (!is_barrier(active)) /* proto-node used by our idle barrier? */
417 		return false;
418 
419 	/*
420 	 * This request is on the kernel_context timeline, and so
421 	 * we can use it to substitute for the pending idle-barrer
422 	 * request that we want to emit on the kernel_context.
423 	 */
424 	return __active_del_barrier(ref, node_from_active(active));
425 }
426 
i915_active_add_request(struct i915_active * ref,struct i915_request * rq)427 int i915_active_add_request(struct i915_active *ref, struct i915_request *rq)
428 {
429 	u64 idx = i915_request_timeline(rq)->fence_context;
430 	struct dma_fence *fence = &rq->fence;
431 	struct i915_active_fence *active;
432 	int err;
433 
434 	/* Prevent reaping in case we malloc/wait while building the tree */
435 	err = i915_active_acquire(ref);
436 	if (err)
437 		return err;
438 
439 	do {
440 		active = active_instance(ref, idx);
441 		if (!active) {
442 			err = -ENOMEM;
443 			goto out;
444 		}
445 
446 		if (replace_barrier(ref, active)) {
447 			RCU_INIT_POINTER(active->fence, NULL);
448 			atomic_dec(&ref->count);
449 		}
450 	} while (unlikely(is_barrier(active)));
451 
452 	fence = __i915_active_fence_set(active, fence);
453 	if (!fence)
454 		__i915_active_acquire(ref);
455 	else
456 		dma_fence_put(fence);
457 
458 out:
459 	i915_active_release(ref);
460 	return err;
461 }
462 
463 static struct dma_fence *
__i915_active_set_fence(struct i915_active * ref,struct i915_active_fence * active,struct dma_fence * fence)464 __i915_active_set_fence(struct i915_active *ref,
465 			struct i915_active_fence *active,
466 			struct dma_fence *fence)
467 {
468 	struct dma_fence *prev;
469 
470 	if (replace_barrier(ref, active)) {
471 		RCU_INIT_POINTER(active->fence, fence);
472 		return NULL;
473 	}
474 
475 	prev = __i915_active_fence_set(active, fence);
476 	if (!prev)
477 		__i915_active_acquire(ref);
478 
479 	return prev;
480 }
481 
482 struct dma_fence *
i915_active_set_exclusive(struct i915_active * ref,struct dma_fence * f)483 i915_active_set_exclusive(struct i915_active *ref, struct dma_fence *f)
484 {
485 	/* We expect the caller to manage the exclusive timeline ordering */
486 	return __i915_active_set_fence(ref, &ref->excl, f);
487 }
488 
i915_active_acquire_if_busy(struct i915_active * ref)489 bool i915_active_acquire_if_busy(struct i915_active *ref)
490 {
491 	debug_active_assert(ref);
492 	return atomic_add_unless(&ref->count, 1, 0);
493 }
494 
__i915_active_activate(struct i915_active * ref)495 static void __i915_active_activate(struct i915_active *ref)
496 {
497 	spin_lock_irq(&ref->tree_lock); /* __active_retire() */
498 	if (!atomic_fetch_inc(&ref->count))
499 		debug_active_activate(ref);
500 	spin_unlock_irq(&ref->tree_lock);
501 }
502 
i915_active_acquire(struct i915_active * ref)503 int i915_active_acquire(struct i915_active *ref)
504 {
505 	int err;
506 
507 	if (i915_active_acquire_if_busy(ref))
508 		return 0;
509 
510 	if (!ref->active) {
511 		__i915_active_activate(ref);
512 		return 0;
513 	}
514 
515 	err = mutex_lock_interruptible(&ref->mutex);
516 	if (err)
517 		return err;
518 
519 	if (likely(!i915_active_acquire_if_busy(ref))) {
520 		err = ref->active(ref);
521 		if (!err)
522 			__i915_active_activate(ref);
523 	}
524 
525 	mutex_unlock(&ref->mutex);
526 
527 	return err;
528 }
529 
i915_active_release(struct i915_active * ref)530 void i915_active_release(struct i915_active *ref)
531 {
532 	debug_active_assert(ref);
533 	active_retire(ref);
534 }
535 
enable_signaling(struct i915_active_fence * active)536 static void enable_signaling(struct i915_active_fence *active)
537 {
538 	struct dma_fence *fence;
539 
540 	if (unlikely(is_barrier(active)))
541 		return;
542 
543 	fence = i915_active_fence_get(active);
544 	if (!fence)
545 		return;
546 
547 	dma_fence_enable_sw_signaling(fence);
548 	dma_fence_put(fence);
549 }
550 
flush_barrier(struct active_node * it)551 static int flush_barrier(struct active_node *it)
552 {
553 	struct intel_engine_cs *engine;
554 
555 	if (likely(!is_barrier(&it->base)))
556 		return 0;
557 
558 	engine = __barrier_to_engine(it);
559 	smp_rmb(); /* serialise with add_active_barriers */
560 	if (!is_barrier(&it->base))
561 		return 0;
562 
563 	return intel_engine_flush_barriers(engine);
564 }
565 
flush_lazy_signals(struct i915_active * ref)566 static int flush_lazy_signals(struct i915_active *ref)
567 {
568 	struct active_node *it, *n;
569 	int err = 0;
570 
571 	enable_signaling(&ref->excl);
572 	rbtree_postorder_for_each_entry_safe(it, n, &ref->tree, node) {
573 		err = flush_barrier(it); /* unconnected idle barrier? */
574 		if (err)
575 			break;
576 
577 		enable_signaling(&it->base);
578 	}
579 
580 	return err;
581 }
582 
__i915_active_wait(struct i915_active * ref,int state)583 int __i915_active_wait(struct i915_active *ref, int state)
584 {
585 	might_sleep();
586 
587 	/* Any fence added after the wait begins will not be auto-signaled */
588 	if (i915_active_acquire_if_busy(ref)) {
589 		int err;
590 
591 		err = flush_lazy_signals(ref);
592 		i915_active_release(ref);
593 		if (err)
594 			return err;
595 
596 		if (___wait_var_event(ref, i915_active_is_idle(ref),
597 				      state, 0, 0, schedule()))
598 			return -EINTR;
599 	}
600 
601 	/*
602 	 * After the wait is complete, the caller may free the active.
603 	 * We have to flush any concurrent retirement before returning.
604 	 */
605 	flush_work(&ref->work);
606 	return 0;
607 }
608 
__await_active(struct i915_active_fence * active,int (* fn)(void * arg,struct dma_fence * fence),void * arg)609 static int __await_active(struct i915_active_fence *active,
610 			  int (*fn)(void *arg, struct dma_fence *fence),
611 			  void *arg)
612 {
613 	struct dma_fence *fence;
614 
615 	if (is_barrier(active)) /* XXX flush the barrier? */
616 		return 0;
617 
618 	fence = i915_active_fence_get(active);
619 	if (fence) {
620 		int err;
621 
622 		err = fn(arg, fence);
623 		dma_fence_put(fence);
624 		if (err < 0)
625 			return err;
626 	}
627 
628 	return 0;
629 }
630 
631 struct wait_barrier {
632 	struct wait_queue_entry base;
633 	struct i915_active *ref;
634 };
635 
636 static int
barrier_wake(wait_queue_entry_t * wq,unsigned int mode,int flags,void * key)637 barrier_wake(wait_queue_entry_t *wq, unsigned int mode, int flags, void *key)
638 {
639 	struct wait_barrier *wb = container_of(wq, typeof(*wb), base);
640 
641 	if (i915_active_is_idle(wb->ref)) {
642 		list_del(&wq->entry);
643 		i915_sw_fence_complete(wq->private);
644 		kfree(wq);
645 	}
646 
647 	return 0;
648 }
649 
__await_barrier(struct i915_active * ref,struct i915_sw_fence * fence)650 static int __await_barrier(struct i915_active *ref, struct i915_sw_fence *fence)
651 {
652 	struct wait_barrier *wb;
653 
654 	wb = kmalloc(sizeof(*wb), GFP_KERNEL);
655 	if (unlikely(!wb))
656 		return -ENOMEM;
657 
658 	GEM_BUG_ON(i915_active_is_idle(ref));
659 	if (!i915_sw_fence_await(fence)) {
660 		kfree(wb);
661 		return -EINVAL;
662 	}
663 
664 	wb->base.flags = 0;
665 	wb->base.func = barrier_wake;
666 	wb->base.private = fence;
667 	wb->ref = ref;
668 
669 	add_wait_queue(__var_waitqueue(ref), &wb->base);
670 	return 0;
671 }
672 
await_active(struct i915_active * ref,unsigned int flags,int (* fn)(void * arg,struct dma_fence * fence),void * arg,struct i915_sw_fence * barrier)673 static int await_active(struct i915_active *ref,
674 			unsigned int flags,
675 			int (*fn)(void *arg, struct dma_fence *fence),
676 			void *arg, struct i915_sw_fence *barrier)
677 {
678 	int err = 0;
679 
680 	if (!i915_active_acquire_if_busy(ref))
681 		return 0;
682 
683 	if (flags & I915_ACTIVE_AWAIT_EXCL &&
684 	    rcu_access_pointer(ref->excl.fence)) {
685 		err = __await_active(&ref->excl, fn, arg);
686 		if (err)
687 			goto out;
688 	}
689 
690 	if (flags & I915_ACTIVE_AWAIT_ACTIVE) {
691 		struct active_node *it, *n;
692 
693 		rbtree_postorder_for_each_entry_safe(it, n, &ref->tree, node) {
694 			err = __await_active(&it->base, fn, arg);
695 			if (err)
696 				goto out;
697 		}
698 	}
699 
700 	if (flags & I915_ACTIVE_AWAIT_BARRIER) {
701 		err = flush_lazy_signals(ref);
702 		if (err)
703 			goto out;
704 
705 		err = __await_barrier(ref, barrier);
706 		if (err)
707 			goto out;
708 	}
709 
710 out:
711 	i915_active_release(ref);
712 	return err;
713 }
714 
rq_await_fence(void * arg,struct dma_fence * fence)715 static int rq_await_fence(void *arg, struct dma_fence *fence)
716 {
717 	return i915_request_await_dma_fence(arg, fence);
718 }
719 
i915_request_await_active(struct i915_request * rq,struct i915_active * ref,unsigned int flags)720 int i915_request_await_active(struct i915_request *rq,
721 			      struct i915_active *ref,
722 			      unsigned int flags)
723 {
724 	return await_active(ref, flags, rq_await_fence, rq, &rq->submit);
725 }
726 
sw_await_fence(void * arg,struct dma_fence * fence)727 static int sw_await_fence(void *arg, struct dma_fence *fence)
728 {
729 	return i915_sw_fence_await_dma_fence(arg, fence, 0,
730 					     GFP_NOWAIT | __GFP_NOWARN);
731 }
732 
i915_sw_fence_await_active(struct i915_sw_fence * fence,struct i915_active * ref,unsigned int flags)733 int i915_sw_fence_await_active(struct i915_sw_fence *fence,
734 			       struct i915_active *ref,
735 			       unsigned int flags)
736 {
737 	return await_active(ref, flags, sw_await_fence, fence, fence);
738 }
739 
i915_active_fini(struct i915_active * ref)740 void i915_active_fini(struct i915_active *ref)
741 {
742 	debug_active_fini(ref);
743 	GEM_BUG_ON(atomic_read(&ref->count));
744 	GEM_BUG_ON(work_pending(&ref->work));
745 	mutex_destroy(&ref->mutex);
746 
747 	if (ref->cache)
748 		kmem_cache_free(slab_cache, ref->cache);
749 }
750 
is_idle_barrier(struct active_node * node,u64 idx)751 static inline bool is_idle_barrier(struct active_node *node, u64 idx)
752 {
753 	return node->timeline == idx && !i915_active_fence_isset(&node->base);
754 }
755 
reuse_idle_barrier(struct i915_active * ref,u64 idx)756 static struct active_node *reuse_idle_barrier(struct i915_active *ref, u64 idx)
757 {
758 	struct rb_node *prev, *p;
759 
760 	if (RB_EMPTY_ROOT(&ref->tree))
761 		return NULL;
762 
763 	GEM_BUG_ON(i915_active_is_idle(ref));
764 
765 	/*
766 	 * Try to reuse any existing barrier nodes already allocated for this
767 	 * i915_active, due to overlapping active phases there is likely a
768 	 * node kept alive (as we reuse before parking). We prefer to reuse
769 	 * completely idle barriers (less hassle in manipulating the llists),
770 	 * but otherwise any will do.
771 	 */
772 	if (ref->cache && is_idle_barrier(ref->cache, idx)) {
773 		p = &ref->cache->node;
774 		goto match;
775 	}
776 
777 	prev = NULL;
778 	p = ref->tree.rb_node;
779 	while (p) {
780 		struct active_node *node =
781 			rb_entry(p, struct active_node, node);
782 
783 		if (is_idle_barrier(node, idx))
784 			goto match;
785 
786 		prev = p;
787 		if (node->timeline < idx)
788 			p = READ_ONCE(p->rb_right);
789 		else
790 			p = READ_ONCE(p->rb_left);
791 	}
792 
793 	/*
794 	 * No quick match, but we did find the leftmost rb_node for the
795 	 * kernel_context. Walk the rb_tree in-order to see if there were
796 	 * any idle-barriers on this timeline that we missed, or just use
797 	 * the first pending barrier.
798 	 */
799 	for (p = prev; p; p = rb_next(p)) {
800 		struct active_node *node =
801 			rb_entry(p, struct active_node, node);
802 		struct intel_engine_cs *engine;
803 
804 		if (node->timeline > idx)
805 			break;
806 
807 		if (node->timeline < idx)
808 			continue;
809 
810 		if (is_idle_barrier(node, idx))
811 			goto match;
812 
813 		/*
814 		 * The list of pending barriers is protected by the
815 		 * kernel_context timeline, which notably we do not hold
816 		 * here. i915_request_add_active_barriers() may consume
817 		 * the barrier before we claim it, so we have to check
818 		 * for success.
819 		 */
820 		engine = __barrier_to_engine(node);
821 		smp_rmb(); /* serialise with add_active_barriers */
822 		if (is_barrier(&node->base) &&
823 		    ____active_del_barrier(ref, node, engine))
824 			goto match;
825 	}
826 
827 	return NULL;
828 
829 match:
830 	spin_lock_irq(&ref->tree_lock);
831 	rb_erase(p, &ref->tree); /* Hide from waits and sibling allocations */
832 	if (p == &ref->cache->node)
833 		WRITE_ONCE(ref->cache, NULL);
834 	spin_unlock_irq(&ref->tree_lock);
835 
836 	return rb_entry(p, struct active_node, node);
837 }
838 
i915_active_acquire_preallocate_barrier(struct i915_active * ref,struct intel_engine_cs * engine)839 int i915_active_acquire_preallocate_barrier(struct i915_active *ref,
840 					    struct intel_engine_cs *engine)
841 {
842 	intel_engine_mask_t tmp, mask = engine->mask;
843 	struct llist_node *first = NULL, *last = NULL;
844 	struct intel_gt *gt = engine->gt;
845 
846 	GEM_BUG_ON(i915_active_is_idle(ref));
847 
848 	/* Wait until the previous preallocation is completed */
849 	while (!llist_empty(&ref->preallocated_barriers))
850 		cond_resched();
851 
852 	/*
853 	 * Preallocate a node for each physical engine supporting the target
854 	 * engine (remember virtual engines have more than one sibling).
855 	 * We can then use the preallocated nodes in
856 	 * i915_active_acquire_barrier()
857 	 */
858 	GEM_BUG_ON(!mask);
859 	for_each_engine_masked(engine, gt, mask, tmp) {
860 		u64 idx = engine->kernel_context->timeline->fence_context;
861 		struct llist_node *prev = first;
862 		struct active_node *node;
863 
864 		rcu_read_lock();
865 		node = reuse_idle_barrier(ref, idx);
866 		rcu_read_unlock();
867 		if (!node) {
868 			node = kmem_cache_alloc(slab_cache, GFP_KERNEL);
869 			if (!node)
870 				goto unwind;
871 
872 			RCU_INIT_POINTER(node->base.fence, NULL);
873 			node->base.cb.func = node_retire;
874 			node->timeline = idx;
875 			node->ref = ref;
876 		}
877 
878 		if (!i915_active_fence_isset(&node->base)) {
879 			/*
880 			 * Mark this as being *our* unconnected proto-node.
881 			 *
882 			 * Since this node is not in any list, and we have
883 			 * decoupled it from the rbtree, we can reuse the
884 			 * request to indicate this is an idle-barrier node
885 			 * and then we can use the rb_node and list pointers
886 			 * for our tracking of the pending barrier.
887 			 */
888 			RCU_INIT_POINTER(node->base.fence, ERR_PTR(-EAGAIN));
889 			node->base.cb.node.prev = (void *)engine;
890 			__i915_active_acquire(ref);
891 		}
892 		GEM_BUG_ON(rcu_access_pointer(node->base.fence) != ERR_PTR(-EAGAIN));
893 
894 		GEM_BUG_ON(barrier_to_engine(node) != engine);
895 		first = barrier_to_ll(node);
896 		first->next = prev;
897 		if (!last)
898 			last = first;
899 		intel_engine_pm_get(engine);
900 	}
901 
902 	GEM_BUG_ON(!llist_empty(&ref->preallocated_barriers));
903 	llist_add_batch(first, last, &ref->preallocated_barriers);
904 
905 	return 0;
906 
907 unwind:
908 	while (first) {
909 		struct active_node *node = barrier_from_ll(first);
910 
911 		first = first->next;
912 
913 		atomic_dec(&ref->count);
914 		intel_engine_pm_put(barrier_to_engine(node));
915 
916 		kmem_cache_free(slab_cache, node);
917 	}
918 	return -ENOMEM;
919 }
920 
i915_active_acquire_barrier(struct i915_active * ref)921 void i915_active_acquire_barrier(struct i915_active *ref)
922 {
923 	struct llist_node *pos, *next;
924 	unsigned long flags;
925 
926 	GEM_BUG_ON(i915_active_is_idle(ref));
927 
928 	/*
929 	 * Transfer the list of preallocated barriers into the
930 	 * i915_active rbtree, but only as proto-nodes. They will be
931 	 * populated by i915_request_add_active_barriers() to point to the
932 	 * request that will eventually release them.
933 	 */
934 	llist_for_each_safe(pos, next, take_preallocated_barriers(ref)) {
935 		struct active_node *node = barrier_from_ll(pos);
936 		struct intel_engine_cs *engine = barrier_to_engine(node);
937 		struct rb_node **p, *parent;
938 
939 		spin_lock_irqsave_nested(&ref->tree_lock, flags,
940 					 SINGLE_DEPTH_NESTING);
941 		parent = NULL;
942 		p = &ref->tree.rb_node;
943 		while (*p) {
944 			struct active_node *it;
945 
946 			parent = *p;
947 
948 			it = rb_entry(parent, struct active_node, node);
949 			if (it->timeline < node->timeline)
950 				p = &parent->rb_right;
951 			else
952 				p = &parent->rb_left;
953 		}
954 		rb_link_node(&node->node, parent, p);
955 		rb_insert_color(&node->node, &ref->tree);
956 		spin_unlock_irqrestore(&ref->tree_lock, flags);
957 
958 		GEM_BUG_ON(!intel_engine_pm_is_awake(engine));
959 		llist_add(barrier_to_ll(node), &engine->barrier_tasks);
960 		intel_engine_pm_put_delay(engine, 2);
961 	}
962 }
963 
ll_to_fence_slot(struct llist_node * node)964 static struct dma_fence **ll_to_fence_slot(struct llist_node *node)
965 {
966 	return __active_fence_slot(&barrier_from_ll(node)->base);
967 }
968 
i915_request_add_active_barriers(struct i915_request * rq)969 void i915_request_add_active_barriers(struct i915_request *rq)
970 {
971 	struct intel_engine_cs *engine = rq->engine;
972 	struct llist_node *node, *next;
973 	unsigned long flags;
974 
975 	GEM_BUG_ON(!intel_context_is_barrier(rq->context));
976 	GEM_BUG_ON(intel_engine_is_virtual(engine));
977 	GEM_BUG_ON(i915_request_timeline(rq) != engine->kernel_context->timeline);
978 
979 	node = llist_del_all(&engine->barrier_tasks);
980 	if (!node)
981 		return;
982 	/*
983 	 * Attach the list of proto-fences to the in-flight request such
984 	 * that the parent i915_active will be released when this request
985 	 * is retired.
986 	 */
987 	spin_lock_irqsave(&rq->lock, flags);
988 	llist_for_each_safe(node, next, node) {
989 		/* serialise with reuse_idle_barrier */
990 		smp_store_mb(*ll_to_fence_slot(node), &rq->fence);
991 		list_add_tail((struct list_head *)node, &rq->fence.cb_list);
992 	}
993 	spin_unlock_irqrestore(&rq->lock, flags);
994 }
995 
996 /*
997  * __i915_active_fence_set: Update the last active fence along its timeline
998  * @active: the active tracker
999  * @fence: the new fence (under construction)
1000  *
1001  * Records the new @fence as the last active fence along its timeline in
1002  * this active tracker, moving the tracking callbacks from the previous
1003  * fence onto this one. Gets and returns a reference to the previous fence
1004  * (if not already completed), which the caller must put after making sure
1005  * that it is executed before the new fence. To ensure that the order of
1006  * fences within the timeline of the i915_active_fence is understood, it
1007  * should be locked by the caller.
1008  */
1009 struct dma_fence *
__i915_active_fence_set(struct i915_active_fence * active,struct dma_fence * fence)1010 __i915_active_fence_set(struct i915_active_fence *active,
1011 			struct dma_fence *fence)
1012 {
1013 	struct dma_fence *prev;
1014 	unsigned long flags;
1015 
1016 	/*
1017 	 * In case of fences embedded in i915_requests, their memory is
1018 	 * SLAB_FAILSAFE_BY_RCU, then it can be reused right after release
1019 	 * by new requests.  Then, there is a risk of passing back a pointer
1020 	 * to a new, completely unrelated fence that reuses the same memory
1021 	 * while tracked under a different active tracker.  Combined with i915
1022 	 * perf open/close operations that build await dependencies between
1023 	 * engine kernel context requests and user requests from different
1024 	 * timelines, this can lead to dependency loops and infinite waits.
1025 	 *
1026 	 * As a countermeasure, we try to get a reference to the active->fence
1027 	 * first, so if we succeed and pass it back to our user then it is not
1028 	 * released and potentially reused by an unrelated request before the
1029 	 * user has a chance to set up an await dependency on it.
1030 	 */
1031 	prev = i915_active_fence_get(active);
1032 	if (fence == prev)
1033 		return fence;
1034 
1035 	GEM_BUG_ON(test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags));
1036 
1037 	/*
1038 	 * Consider that we have two threads arriving (A and B), with
1039 	 * C already resident as the active->fence.
1040 	 *
1041 	 * Both A and B have got a reference to C or NULL, depending on the
1042 	 * timing of the interrupt handler.  Let's assume that if A has got C
1043 	 * then it has locked C first (before B).
1044 	 *
1045 	 * Note the strong ordering of the timeline also provides consistent
1046 	 * nesting rules for the fence->lock; the inner lock is always the
1047 	 * older lock.
1048 	 */
1049 	spin_lock_irqsave(fence->lock, flags);
1050 	if (prev)
1051 		spin_lock_nested(prev->lock, SINGLE_DEPTH_NESTING);
1052 
1053 	/*
1054 	 * A does the cmpxchg first, and so it sees C or NULL, as before, or
1055 	 * something else, depending on the timing of other threads and/or
1056 	 * interrupt handler.  If not the same as before then A unlocks C if
1057 	 * applicable and retries, starting from an attempt to get a new
1058 	 * active->fence.  Meanwhile, B follows the same path as A.
1059 	 * Once A succeeds with cmpxch, B fails again, retires, gets A from
1060 	 * active->fence, locks it as soon as A completes, and possibly
1061 	 * succeeds with cmpxchg.
1062 	 */
1063 	while (cmpxchg(__active_fence_slot(active), prev, fence) != prev) {
1064 		if (prev) {
1065 			spin_unlock(prev->lock);
1066 			dma_fence_put(prev);
1067 		}
1068 		spin_unlock_irqrestore(fence->lock, flags);
1069 
1070 		prev = i915_active_fence_get(active);
1071 		GEM_BUG_ON(prev == fence);
1072 
1073 		spin_lock_irqsave(fence->lock, flags);
1074 		if (prev)
1075 			spin_lock_nested(prev->lock, SINGLE_DEPTH_NESTING);
1076 	}
1077 
1078 	/*
1079 	 * If prev is NULL then the previous fence must have been signaled
1080 	 * and we know that we are first on the timeline.  If it is still
1081 	 * present then, having the lock on that fence already acquired, we
1082 	 * serialise with the interrupt handler, in the process of removing it
1083 	 * from any future interrupt callback.  A will then wait on C before
1084 	 * executing (if present).
1085 	 *
1086 	 * As B is second, it sees A as the previous fence and so waits for
1087 	 * it to complete its transition and takes over the occupancy for
1088 	 * itself -- remembering that it needs to wait on A before executing.
1089 	 */
1090 	if (prev) {
1091 		__list_del_entry(&active->cb.node);
1092 		spin_unlock(prev->lock); /* serialise with prev->cb_list */
1093 	}
1094 	list_add_tail(&active->cb.node, &fence->cb_list);
1095 	spin_unlock_irqrestore(fence->lock, flags);
1096 
1097 	return prev;
1098 }
1099 
i915_active_fence_set(struct i915_active_fence * active,struct i915_request * rq)1100 int i915_active_fence_set(struct i915_active_fence *active,
1101 			  struct i915_request *rq)
1102 {
1103 	struct dma_fence *fence;
1104 	int err = 0;
1105 
1106 	/* Must maintain timeline ordering wrt previous active requests */
1107 	fence = __i915_active_fence_set(active, &rq->fence);
1108 	if (fence) {
1109 		err = i915_request_await_dma_fence(rq, fence);
1110 		dma_fence_put(fence);
1111 	}
1112 
1113 	return err;
1114 }
1115 
i915_active_noop(struct dma_fence * fence,struct dma_fence_cb * cb)1116 void i915_active_noop(struct dma_fence *fence, struct dma_fence_cb *cb)
1117 {
1118 	active_fence_cb(fence, cb);
1119 }
1120 
1121 struct auto_active {
1122 	struct i915_active base;
1123 	struct kref ref;
1124 };
1125 
i915_active_get(struct i915_active * ref)1126 struct i915_active *i915_active_get(struct i915_active *ref)
1127 {
1128 	struct auto_active *aa = container_of(ref, typeof(*aa), base);
1129 
1130 	kref_get(&aa->ref);
1131 	return &aa->base;
1132 }
1133 
auto_release(struct kref * ref)1134 static void auto_release(struct kref *ref)
1135 {
1136 	struct auto_active *aa = container_of(ref, typeof(*aa), ref);
1137 
1138 	i915_active_fini(&aa->base);
1139 	kfree(aa);
1140 }
1141 
i915_active_put(struct i915_active * ref)1142 void i915_active_put(struct i915_active *ref)
1143 {
1144 	struct auto_active *aa = container_of(ref, typeof(*aa), base);
1145 
1146 	kref_put(&aa->ref, auto_release);
1147 }
1148 
auto_active(struct i915_active * ref)1149 static int auto_active(struct i915_active *ref)
1150 {
1151 	i915_active_get(ref);
1152 	return 0;
1153 }
1154 
auto_retire(struct i915_active * ref)1155 static void auto_retire(struct i915_active *ref)
1156 {
1157 	i915_active_put(ref);
1158 }
1159 
i915_active_create(void)1160 struct i915_active *i915_active_create(void)
1161 {
1162 	struct auto_active *aa;
1163 
1164 	aa = kmalloc(sizeof(*aa), GFP_KERNEL);
1165 	if (!aa)
1166 		return NULL;
1167 
1168 	kref_init(&aa->ref);
1169 	i915_active_init(&aa->base, auto_active, auto_retire, 0);
1170 
1171 	return &aa->base;
1172 }
1173 
1174 #if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
1175 #include "selftests/i915_active.c"
1176 #endif
1177 
i915_active_module_exit(void)1178 void i915_active_module_exit(void)
1179 {
1180 	kmem_cache_destroy(slab_cache);
1181 }
1182 
i915_active_module_init(void)1183 int __init i915_active_module_init(void)
1184 {
1185 	slab_cache = KMEM_CACHE(active_node, SLAB_HWCACHE_ALIGN);
1186 	if (!slab_cache)
1187 		return -ENOMEM;
1188 
1189 	return 0;
1190 }
1191