i915_active.c

   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 */
  24static struct kmem_cache *slab_cache;
  25
  26struct 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
  35static inline struct active_node *
  36node_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
  43static inline bool is_barrier(const struct i915_active_fence *active)
  44{
  45	return IS_ERR(rcu_access_pointer(active->fence));
  46}
  47
  48static 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
  54static inline struct intel_engine_cs *
  55__barrier_to_engine(struct active_node *node)
  56{
  57	return (struct intel_engine_cs *)READ_ONCE(node->base.cb.node.prev);
  58}
  59
  60static inline struct intel_engine_cs *
  61barrier_to_engine(struct active_node *node)
  62{
  63	GEM_BUG_ON(!is_barrier(&node->base));
  64	return __barrier_to_engine(node);
  65}
  66
  67static 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
  75static 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
  82static const struct debug_obj_descr active_debug_desc = {
  83	.name = "i915_active",
  84	.debug_hint = active_debug_hint,
  85};
  86
  87static void debug_active_init(struct i915_active *ref)
  88{
  89	debug_object_init(ref, &active_debug_desc);
  90}
  91
  92static 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
  98static 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
 105static void debug_active_fini(struct i915_active *ref)
 106{
 107	debug_object_free(ref, &active_debug_desc);
 108}
 109
 110static void debug_active_assert(struct i915_active *ref)
 111{
 112	debug_object_assert_init(ref, &active_debug_desc);
 113}
 114
 115#else
 116
 117static inline void debug_active_init(struct i915_active *ref) { }
 118static inline void debug_active_activate(struct i915_active *ref) { }
 119static inline void debug_active_deactivate(struct i915_active *ref) { }
 120static inline void debug_active_fini(struct i915_active *ref) { }
 121static inline void debug_active_assert(struct i915_active *ref) { }
 122
 123#endif
 124
 125static void
 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
 176static void
 177active_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
 188static void
 189active_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
 203static inline struct dma_fence **
 204__active_fence_slot(struct i915_active_fence *active)
 205{
 206	return (struct dma_fence ** __force)&active->fence;
 207}
 208
 209static inline bool
 210active_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
 218static void
 219node_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
 225static void
 226excl_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
 232static 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 succeed).
 261		 */
 262		if (!cached && try_cmpxchg64(&it->timeline, &cached, idx))
 263			return it;
 264	}
 265
 266	BUILD_BUG_ON(offsetof(typeof(*it), node));
 267
 268	/* While active, the tree can only be built; not destroyed */
 269	GEM_BUG_ON(i915_active_is_idle(ref));
 270
 271	it = fetch_node(ref->tree.rb_node);
 272	while (it) {
 273		if (it->timeline < idx) {
 274			it = fetch_node(it->node.rb_right);
 275		} else if (it->timeline > idx) {
 276			it = fetch_node(it->node.rb_left);
 277		} else {
 278			WRITE_ONCE(ref->cache, it);
 279			break;
 280		}
 281	}
 282
 283	/* NB: If the tree rotated beneath us, we may miss our target. */
 284	return it;
 285}
 286
 287static struct i915_active_fence *
 288active_instance(struct i915_active *ref, u64 idx)
 289{
 290	struct active_node *node;
 291	struct rb_node **p, *parent;
 292
 293	node = __active_lookup(ref, idx);
 294	if (likely(node))
 295		return &node->base;
 296
 297	spin_lock_irq(&ref->tree_lock);
 298	GEM_BUG_ON(i915_active_is_idle(ref));
 299
 300	parent = NULL;
 301	p = &ref->tree.rb_node;
 302	while (*p) {
 303		parent = *p;
 304
 305		node = rb_entry(parent, struct active_node, node);
 306		if (node->timeline == idx)
 307			goto out;
 308
 309		if (node->timeline < idx)
 310			p = &parent->rb_right;
 311		else
 312			p = &parent->rb_left;
 313	}
 314
 315	/*
 316	 * XXX: We should preallocate this before i915_active_ref() is ever
 317	 *  called, but we cannot call into fs_reclaim() anyway, so use GFP_ATOMIC.
 318	 */
 319	node = kmem_cache_alloc(slab_cache, GFP_ATOMIC);
 320	if (!node)
 321		goto out;
 322
 323	__i915_active_fence_init(&node->base, NULL, node_retire);
 324	node->ref = ref;
 325	node->timeline = idx;
 326
 327	rb_link_node(&node->node, parent, p);
 328	rb_insert_color(&node->node, &ref->tree);
 329
 330out:
 331	WRITE_ONCE(ref->cache, node);
 332	spin_unlock_irq(&ref->tree_lock);
 333
 334	return &node->base;
 335}
 336
 337void __i915_active_init(struct i915_active *ref,
 338			int (*active)(struct i915_active *ref),
 339			void (*retire)(struct i915_active *ref),
 340			unsigned long flags,
 341			struct lock_class_key *mkey,
 342			struct lock_class_key *wkey)
 343{
 344	debug_active_init(ref);
 345
 346	ref->flags = flags;
 347	ref->active = active;
 348	ref->retire = retire;
 349
 350	spin_lock_init(&ref->tree_lock);
 351	ref->tree = RB_ROOT;
 352	ref->cache = NULL;
 353
 354	init_llist_head(&ref->preallocated_barriers);
 355	atomic_set(&ref->count, 0);
 356	__mutex_init(&ref->mutex, "i915_active", mkey);
 357	__i915_active_fence_init(&ref->excl, NULL, excl_retire);
 358	INIT_WORK(&ref->work, active_work);
 359#if IS_ENABLED(CONFIG_LOCKDEP)
 360	lockdep_init_map(&ref->work.lockdep_map, "i915_active.work", wkey, 0);
 361#endif
 362}
 363
 364static bool ____active_del_barrier(struct i915_active *ref,
 365				   struct active_node *node,
 366				   struct intel_engine_cs *engine)
 367
 368{
 369	struct llist_node *head = NULL, *tail = NULL;
 370	struct llist_node *pos, *next;
 371
 372	GEM_BUG_ON(node->timeline != engine->kernel_context->timeline->fence_context);
 373
 374	/*
 375	 * Rebuild the llist excluding our node. We may perform this
 376	 * outside of the kernel_context timeline mutex and so someone
 377	 * else may be manipulating the engine->barrier_tasks, in
 378	 * which case either we or they will be upset :)
 379	 *
 380	 * A second __active_del_barrier() will report failure to claim
 381	 * the active_node and the caller will just shrug and know not to
 382	 * claim ownership of its node.
 383	 *
 384	 * A concurrent i915_request_add_active_barriers() will miss adding
 385	 * any of the tasks, but we will try again on the next -- and since
 386	 * we are actively using the barrier, we know that there will be
 387	 * at least another opportunity when we idle.
 388	 */
 389	llist_for_each_safe(pos, next, llist_del_all(&engine->barrier_tasks)) {
 390		if (node == barrier_from_ll(pos)) {
 391			node = NULL;
 392			continue;
 393		}
 394
 395		pos->next = head;
 396		head = pos;
 397		if (!tail)
 398			tail = pos;
 399	}
 400	if (head)
 401		llist_add_batch(head, tail, &engine->barrier_tasks);
 402
 403	return !node;
 404}
 405
 406static bool
 407__active_del_barrier(struct i915_active *ref, struct active_node *node)
 408{
 409	return ____active_del_barrier(ref, node, barrier_to_engine(node));
 410}
 411
 412static bool
 413replace_barrier(struct i915_active *ref, struct i915_active_fence *active)
 414{
 415	if (!is_barrier(active)) /* proto-node used by our idle barrier? */
 416		return false;
 417
 418	/*
 419	 * This request is on the kernel_context timeline, and so
 420	 * we can use it to substitute for the pending idle-barrer
 421	 * request that we want to emit on the kernel_context.
 422	 */
 423	return __active_del_barrier(ref, node_from_active(active));
 424}
 425
 426int i915_active_add_request(struct i915_active *ref, struct i915_request *rq)
 427{
 428	u64 idx = i915_request_timeline(rq)->fence_context;
 429	struct dma_fence *fence = &rq->fence;
 430	struct i915_active_fence *active;
 431	int err;
 432
 433	/* Prevent reaping in case we malloc/wait while building the tree */
 434	err = i915_active_acquire(ref);
 435	if (err)
 436		return err;
 437
 438	do {
 439		active = active_instance(ref, idx);
 440		if (!active) {
 441			err = -ENOMEM;
 442			goto out;
 443		}
 444
 445		if (replace_barrier(ref, active)) {
 446			RCU_INIT_POINTER(active->fence, NULL);
 447			atomic_dec(&ref->count);
 448		}
 449	} while (unlikely(is_barrier(active)));
 450
 451	fence = __i915_active_fence_set(active, fence);
 452	if (!fence)
 453		__i915_active_acquire(ref);
 454	else
 455		dma_fence_put(fence);
 456
 457out:
 458	i915_active_release(ref);
 459	return err;
 460}
 461
 462static struct dma_fence *
 463__i915_active_set_fence(struct i915_active *ref,
 464			struct i915_active_fence *active,
 465			struct dma_fence *fence)
 466{
 467	struct dma_fence *prev;
 468
 469	if (replace_barrier(ref, active)) {
 470		RCU_INIT_POINTER(active->fence, fence);
 471		return NULL;
 472	}
 473
 474	prev = __i915_active_fence_set(active, fence);
 475	if (!prev)
 476		__i915_active_acquire(ref);
 477
 478	return prev;
 479}
 480
 481struct dma_fence *
 482i915_active_set_exclusive(struct i915_active *ref, struct dma_fence *f)
 483{
 484	/* We expect the caller to manage the exclusive timeline ordering */
 485	return __i915_active_set_fence(ref, &ref->excl, f);
 486}
 487
 488bool i915_active_acquire_if_busy(struct i915_active *ref)
 489{
 490	debug_active_assert(ref);
 491	return atomic_add_unless(&ref->count, 1, 0);
 492}
 493
 494static void __i915_active_activate(struct i915_active *ref)
 495{
 496	spin_lock_irq(&ref->tree_lock); /* __active_retire() */
 497	if (!atomic_fetch_inc(&ref->count))
 498		debug_active_activate(ref);
 499	spin_unlock_irq(&ref->tree_lock);
 500}
 501
 502int i915_active_acquire(struct i915_active *ref)
 503{
 504	int err;
 505
 506	if (i915_active_acquire_if_busy(ref))
 507		return 0;
 508
 509	if (!ref->active) {
 510		__i915_active_activate(ref);
 511		return 0;
 512	}
 513
 514	err = mutex_lock_interruptible(&ref->mutex);
 515	if (err)
 516		return err;
 517
 518	if (likely(!i915_active_acquire_if_busy(ref))) {
 519		err = ref->active(ref);
 520		if (!err)
 521			__i915_active_activate(ref);
 522	}
 523
 524	mutex_unlock(&ref->mutex);
 525
 526	return err;
 527}
 528
 529void i915_active_release(struct i915_active *ref)
 530{
 531	debug_active_assert(ref);
 532	active_retire(ref);
 533}
 534
 535static void enable_signaling(struct i915_active_fence *active)
 536{
 537	struct dma_fence *fence;
 538
 539	if (unlikely(is_barrier(active)))
 540		return;
 541
 542	fence = i915_active_fence_get(active);
 543	if (!fence)
 544		return;
 545
 546	dma_fence_enable_sw_signaling(fence);
 547	dma_fence_put(fence);
 548}
 549
 550static int flush_barrier(struct active_node *it)
 551{
 552	struct intel_engine_cs *engine;
 553
 554	if (likely(!is_barrier(&it->base)))
 555		return 0;
 556
 557	engine = __barrier_to_engine(it);
 558	smp_rmb(); /* serialise with add_active_barriers */
 559	if (!is_barrier(&it->base))
 560		return 0;
 561
 562	return intel_engine_flush_barriers(engine);
 563}
 564
 565static int flush_lazy_signals(struct i915_active *ref)
 566{
 567	struct active_node *it, *n;
 568	int err = 0;
 569
 570	enable_signaling(&ref->excl);
 571	rbtree_postorder_for_each_entry_safe(it, n, &ref->tree, node) {
 572		err = flush_barrier(it); /* unconnected idle barrier? */
 573		if (err)
 574			break;
 575
 576		enable_signaling(&it->base);
 577	}
 578
 579	return err;
 580}
 581
 582int __i915_active_wait(struct i915_active *ref, int state)
 583{
 584	might_sleep();
 585
 586	/* Any fence added after the wait begins will not be auto-signaled */
 587	if (i915_active_acquire_if_busy(ref)) {
 588		int err;
 589
 590		err = flush_lazy_signals(ref);
 591		i915_active_release(ref);
 592		if (err)
 593			return err;
 594
 595		if (___wait_var_event(ref, i915_active_is_idle(ref),
 596				      state, 0, 0, schedule()))
 597			return -EINTR;
 598	}
 599
 600	/*
 601	 * After the wait is complete, the caller may free the active.
 602	 * We have to flush any concurrent retirement before returning.
 603	 */
 604	flush_work(&ref->work);
 605	return 0;
 606}
 607
 608static int __await_active(struct i915_active_fence *active,
 609			  int (*fn)(void *arg, struct dma_fence *fence),
 610			  void *arg)
 611{
 612	struct dma_fence *fence;
 613
 614	if (is_barrier(active)) /* XXX flush the barrier? */
 615		return 0;
 616
 617	fence = i915_active_fence_get(active);
 618	if (fence) {
 619		int err;
 620
 621		err = fn(arg, fence);
 622		dma_fence_put(fence);
 623		if (err < 0)
 624			return err;
 625	}
 626
 627	return 0;
 628}
 629
 630struct wait_barrier {
 631	struct wait_queue_entry base;
 632	struct i915_active *ref;
 633};
 634
 635static int
 636barrier_wake(wait_queue_entry_t *wq, unsigned int mode, int flags, void *key)
 637{
 638	struct wait_barrier *wb = container_of(wq, typeof(*wb), base);
 639
 640	if (i915_active_is_idle(wb->ref)) {
 641		list_del(&wq->entry);
 642		i915_sw_fence_complete(wq->private);
 643		kfree(wq);
 644	}
 645
 646	return 0;
 647}
 648
 649static int __await_barrier(struct i915_active *ref, struct i915_sw_fence *fence)
 650{
 651	struct wait_barrier *wb;
 652
 653	wb = kmalloc(sizeof(*wb), GFP_KERNEL);
 654	if (unlikely(!wb))
 655		return -ENOMEM;
 656
 657	GEM_BUG_ON(i915_active_is_idle(ref));
 658	if (!i915_sw_fence_await(fence)) {
 659		kfree(wb);
 660		return -EINVAL;
 661	}
 662
 663	wb->base.flags = 0;
 664	wb->base.func = barrier_wake;
 665	wb->base.private = fence;
 666	wb->ref = ref;
 667
 668	add_wait_queue(__var_waitqueue(ref), &wb->base);
 669	return 0;
 670}
 671
 672static int await_active(struct i915_active *ref,
 673			unsigned int flags,
 674			int (*fn)(void *arg, struct dma_fence *fence),
 675			void *arg, struct i915_sw_fence *barrier)
 676{
 677	int err = 0;
 678
 679	if (!i915_active_acquire_if_busy(ref))
 680		return 0;
 681
 682	if (flags & I915_ACTIVE_AWAIT_EXCL &&
 683	    rcu_access_pointer(ref->excl.fence)) {
 684		err = __await_active(&ref->excl, fn, arg);
 685		if (err)
 686			goto out;
 687	}
 688
 689	if (flags & I915_ACTIVE_AWAIT_ACTIVE) {
 690		struct active_node *it, *n;
 691
 692		rbtree_postorder_for_each_entry_safe(it, n, &ref->tree, node) {
 693			err = __await_active(&it->base, fn, arg);
 694			if (err)
 695				goto out;
 696		}
 697	}
 698
 699	if (flags & I915_ACTIVE_AWAIT_BARRIER) {
 700		err = flush_lazy_signals(ref);
 701		if (err)
 702			goto out;
 703
 704		err = __await_barrier(ref, barrier);
 705		if (err)
 706			goto out;
 707	}
 708
 709out:
 710	i915_active_release(ref);
 711	return err;
 712}
 713
 714static int rq_await_fence(void *arg, struct dma_fence *fence)
 715{
 716	return i915_request_await_dma_fence(arg, fence);
 717}
 718
 719int i915_request_await_active(struct i915_request *rq,
 720			      struct i915_active *ref,
 721			      unsigned int flags)
 722{
 723	return await_active(ref, flags, rq_await_fence, rq, &rq->submit);
 724}
 725
 726static int sw_await_fence(void *arg, struct dma_fence *fence)
 727{
 728	return i915_sw_fence_await_dma_fence(arg, fence, 0,
 729					     GFP_NOWAIT | __GFP_NOWARN);
 730}
 731
 732int i915_sw_fence_await_active(struct i915_sw_fence *fence,
 733			       struct i915_active *ref,
 734			       unsigned int flags)
 735{
 736	return await_active(ref, flags, sw_await_fence, fence, fence);
 737}
 738
 739void i915_active_fini(struct i915_active *ref)
 740{
 741	debug_active_fini(ref);
 742	GEM_BUG_ON(atomic_read(&ref->count));
 743	GEM_BUG_ON(work_pending(&ref->work));
 744	mutex_destroy(&ref->mutex);
 745
 746	if (ref->cache)
 747		kmem_cache_free(slab_cache, ref->cache);
 748}
 749
 750static inline bool is_idle_barrier(struct active_node *node, u64 idx)
 751{
 752	return node->timeline == idx && !i915_active_fence_isset(&node->base);
 753}
 754
 755static struct active_node *reuse_idle_barrier(struct i915_active *ref, u64 idx)
 756{
 757	struct rb_node *prev, *p;
 758
 759	if (RB_EMPTY_ROOT(&ref->tree))
 760		return NULL;
 761
 762	GEM_BUG_ON(i915_active_is_idle(ref));
 763
 764	/*
 765	 * Try to reuse any existing barrier nodes already allocated for this
 766	 * i915_active, due to overlapping active phases there is likely a
 767	 * node kept alive (as we reuse before parking). We prefer to reuse
 768	 * completely idle barriers (less hassle in manipulating the llists),
 769	 * but otherwise any will do.
 770	 */
 771	if (ref->cache && is_idle_barrier(ref->cache, idx)) {
 772		p = &ref->cache->node;
 773		goto match;
 774	}
 775
 776	prev = NULL;
 777	p = ref->tree.rb_node;
 778	while (p) {
 779		struct active_node *node =
 780			rb_entry(p, struct active_node, node);
 781
 782		if (is_idle_barrier(node, idx))
 783			goto match;
 784
 785		prev = p;
 786		if (node->timeline < idx)
 787			p = READ_ONCE(p->rb_right);
 788		else
 789			p = READ_ONCE(p->rb_left);
 790	}
 791
 792	/*
 793	 * No quick match, but we did find the leftmost rb_node for the
 794	 * kernel_context. Walk the rb_tree in-order to see if there were
 795	 * any idle-barriers on this timeline that we missed, or just use
 796	 * the first pending barrier.
 797	 */
 798	for (p = prev; p; p = rb_next(p)) {
 799		struct active_node *node =
 800			rb_entry(p, struct active_node, node);
 801		struct intel_engine_cs *engine;
 802
 803		if (node->timeline > idx)
 804			break;
 805
 806		if (node->timeline < idx)
 807			continue;
 808
 809		if (is_idle_barrier(node, idx))
 810			goto match;
 811
 812		/*
 813		 * The list of pending barriers is protected by the
 814		 * kernel_context timeline, which notably we do not hold
 815		 * here. i915_request_add_active_barriers() may consume
 816		 * the barrier before we claim it, so we have to check
 817		 * for success.
 818		 */
 819		engine = __barrier_to_engine(node);
 820		smp_rmb(); /* serialise with add_active_barriers */
 821		if (is_barrier(&node->base) &&
 822		    ____active_del_barrier(ref, node, engine))
 823			goto match;
 824	}
 825
 826	return NULL;
 827
 828match:
 829	spin_lock_irq(&ref->tree_lock);
 830	rb_erase(p, &ref->tree); /* Hide from waits and sibling allocations */
 831	if (p == &ref->cache->node)
 832		WRITE_ONCE(ref->cache, NULL);
 833	spin_unlock_irq(&ref->tree_lock);
 834
 835	return rb_entry(p, struct active_node, node);
 836}
 837
 838int i915_active_acquire_preallocate_barrier(struct i915_active *ref,
 839					    struct intel_engine_cs *engine)
 840{
 841	intel_engine_mask_t tmp, mask = engine->mask;
 842	struct llist_node *first = NULL, *last = NULL;
 843	struct intel_gt *gt = engine->gt;
 844
 845	GEM_BUG_ON(i915_active_is_idle(ref));
 846
 847	/* Wait until the previous preallocation is completed */
 848	while (!llist_empty(&ref->preallocated_barriers))
 849		cond_resched();
 850
 851	/*
 852	 * Preallocate a node for each physical engine supporting the target
 853	 * engine (remember virtual engines have more than one sibling).
 854	 * We can then use the preallocated nodes in
 855	 * i915_active_acquire_barrier()
 856	 */
 857	GEM_BUG_ON(!mask);
 858	for_each_engine_masked(engine, gt, mask, tmp) {
 859		u64 idx = engine->kernel_context->timeline->fence_context;
 860		struct llist_node *prev = first;
 861		struct active_node *node;
 862
 863		rcu_read_lock();
 864		node = reuse_idle_barrier(ref, idx);
 865		rcu_read_unlock();
 866		if (!node) {
 867			node = kmem_cache_alloc(slab_cache, GFP_KERNEL);
 868			if (!node)
 869				goto unwind;
 870
 871			RCU_INIT_POINTER(node->base.fence, NULL);
 872			node->base.cb.func = node_retire;
 873			node->timeline = idx;
 874			node->ref = ref;
 875		}
 876
 877		if (!i915_active_fence_isset(&node->base)) {
 878			/*
 879			 * Mark this as being *our* unconnected proto-node.
 880			 *
 881			 * Since this node is not in any list, and we have
 882			 * decoupled it from the rbtree, we can reuse the
 883			 * request to indicate this is an idle-barrier node
 884			 * and then we can use the rb_node and list pointers
 885			 * for our tracking of the pending barrier.
 886			 */
 887			RCU_INIT_POINTER(node->base.fence, ERR_PTR(-EAGAIN));
 888			node->base.cb.node.prev = (void *)engine;
 889			__i915_active_acquire(ref);
 890		}
 891		GEM_BUG_ON(rcu_access_pointer(node->base.fence) != ERR_PTR(-EAGAIN));
 892
 893		GEM_BUG_ON(barrier_to_engine(node) != engine);
 894		first = barrier_to_ll(node);
 895		first->next = prev;
 896		if (!last)
 897			last = first;
 898		intel_engine_pm_get(engine);
 899	}
 900
 901	GEM_BUG_ON(!llist_empty(&ref->preallocated_barriers));
 902	llist_add_batch(first, last, &ref->preallocated_barriers);
 903
 904	return 0;
 905
 906unwind:
 907	while (first) {
 908		struct active_node *node = barrier_from_ll(first);
 909
 910		first = first->next;
 911
 912		atomic_dec(&ref->count);
 913		intel_engine_pm_put(barrier_to_engine(node));
 914
 915		kmem_cache_free(slab_cache, node);
 916	}
 917	return -ENOMEM;
 918}
 919
 920void i915_active_acquire_barrier(struct i915_active *ref)
 921{
 922	struct llist_node *pos, *next;
 923	unsigned long flags;
 924
 925	GEM_BUG_ON(i915_active_is_idle(ref));
 926
 927	/*
 928	 * Transfer the list of preallocated barriers into the
 929	 * i915_active rbtree, but only as proto-nodes. They will be
 930	 * populated by i915_request_add_active_barriers() to point to the
 931	 * request that will eventually release them.
 932	 */
 933	llist_for_each_safe(pos, next, take_preallocated_barriers(ref)) {
 934		struct active_node *node = barrier_from_ll(pos);
 935		struct intel_engine_cs *engine = barrier_to_engine(node);
 936		struct rb_node **p, *parent;
 937
 938		spin_lock_irqsave_nested(&ref->tree_lock, flags,
 939					 SINGLE_DEPTH_NESTING);
 940		parent = NULL;
 941		p = &ref->tree.rb_node;
 942		while (*p) {
 943			struct active_node *it;
 944
 945			parent = *p;
 946
 947			it = rb_entry(parent, struct active_node, node);
 948			if (it->timeline < node->timeline)
 949				p = &parent->rb_right;
 950			else
 951				p = &parent->rb_left;
 952		}
 953		rb_link_node(&node->node, parent, p);
 954		rb_insert_color(&node->node, &ref->tree);
 955		spin_unlock_irqrestore(&ref->tree_lock, flags);
 956
 957		GEM_BUG_ON(!intel_engine_pm_is_awake(engine));
 958		llist_add(barrier_to_ll(node), &engine->barrier_tasks);
 959		intel_engine_pm_put_delay(engine, 2);
 960	}
 961}
 962
 963static struct dma_fence **ll_to_fence_slot(struct llist_node *node)
 964{
 965	return __active_fence_slot(&barrier_from_ll(node)->base);
 966}
 967
 968void i915_request_add_active_barriers(struct i915_request *rq)
 969{
 970	struct intel_engine_cs *engine = rq->engine;
 971	struct llist_node *node, *next;
 972	unsigned long flags;
 973
 974	GEM_BUG_ON(!intel_context_is_barrier(rq->context));
 975	GEM_BUG_ON(intel_engine_is_virtual(engine));
 976	GEM_BUG_ON(i915_request_timeline(rq) != engine->kernel_context->timeline);
 977
 978	node = llist_del_all(&engine->barrier_tasks);
 979	if (!node)
 980		return;
 981	/*
 982	 * Attach the list of proto-fences to the in-flight request such
 983	 * that the parent i915_active will be released when this request
 984	 * is retired.
 985	 */
 986	spin_lock_irqsave(&rq->lock, flags);
 987	llist_for_each_safe(node, next, node) {
 988		/* serialise with reuse_idle_barrier */
 989		smp_store_mb(*ll_to_fence_slot(node), &rq->fence);
 990		list_add_tail((struct list_head *)node, &rq->fence.cb_list);
 991	}
 992	spin_unlock_irqrestore(&rq->lock, flags);
 993}
 994
 995/*
 996 * __i915_active_fence_set: Update the last active fence along its timeline
 997 * @active: the active tracker
 998 * @fence: the new fence (under construction)
 999 *
1000 * Records the new @fence as the last active fence along its timeline in
1001 * this active tracker, moving the tracking callbacks from the previous
1002 * fence onto this one. Gets and returns a reference to the previous fence
1003 * (if not already completed), which the caller must put after making sure
1004 * that it is executed before the new fence. To ensure that the order of
1005 * fences within the timeline of the i915_active_fence is understood, it
1006 * should be locked by the caller.
1007 */
1008struct dma_fence *
1009__i915_active_fence_set(struct i915_active_fence *active,
1010			struct dma_fence *fence)
1011{
1012	struct dma_fence *prev;
1013	unsigned long flags;
1014
1015	/*
1016	 * In case of fences embedded in i915_requests, their memory is
1017	 * SLAB_FAILSAFE_BY_RCU, then it can be reused right after release
1018	 * by new requests.  Then, there is a risk of passing back a pointer
1019	 * to a new, completely unrelated fence that reuses the same memory
1020	 * while tracked under a different active tracker.  Combined with i915
1021	 * perf open/close operations that build await dependencies between
1022	 * engine kernel context requests and user requests from different
1023	 * timelines, this can lead to dependency loops and infinite waits.
1024	 *
1025	 * As a countermeasure, we try to get a reference to the active->fence
1026	 * first, so if we succeed and pass it back to our user then it is not
1027	 * released and potentially reused by an unrelated request before the
1028	 * user has a chance to set up an await dependency on it.
1029	 */
1030	prev = i915_active_fence_get(active);
1031	if (fence == prev)
1032		return fence;
1033
1034	GEM_BUG_ON(test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags));
1035
1036	/*
1037	 * Consider that we have two threads arriving (A and B), with
1038	 * C already resident as the active->fence.
1039	 *
1040	 * Both A and B have got a reference to C or NULL, depending on the
1041	 * timing of the interrupt handler.  Let's assume that if A has got C
1042	 * then it has locked C first (before B).
1043	 *
1044	 * Note the strong ordering of the timeline also provides consistent
1045	 * nesting rules for the fence->lock; the inner lock is always the
1046	 * older lock.
1047	 */
1048	spin_lock_irqsave(fence->lock, flags);
1049	if (prev)
1050		spin_lock_nested(prev->lock, SINGLE_DEPTH_NESTING);
1051
1052	/*
1053	 * A does the cmpxchg first, and so it sees C or NULL, as before, or
1054	 * something else, depending on the timing of other threads and/or
1055	 * interrupt handler.  If not the same as before then A unlocks C if
1056	 * applicable and retries, starting from an attempt to get a new
1057	 * active->fence.  Meanwhile, B follows the same path as A.
1058	 * Once A succeeds with cmpxch, B fails again, retires, gets A from
1059	 * active->fence, locks it as soon as A completes, and possibly
1060	 * succeeds with cmpxchg.
1061	 */
1062	while (cmpxchg(__active_fence_slot(active), prev, fence) != prev) {
1063		if (prev) {
1064			spin_unlock(prev->lock);
1065			dma_fence_put(prev);
1066		}
1067		spin_unlock_irqrestore(fence->lock, flags);
1068
1069		prev = i915_active_fence_get(active);
1070		GEM_BUG_ON(prev == fence);
1071
1072		spin_lock_irqsave(fence->lock, flags);
1073		if (prev)
1074			spin_lock_nested(prev->lock, SINGLE_DEPTH_NESTING);
1075	}
1076
1077	/*
1078	 * If prev is NULL then the previous fence must have been signaled
1079	 * and we know that we are first on the timeline.  If it is still
1080	 * present then, having the lock on that fence already acquired, we
1081	 * serialise with the interrupt handler, in the process of removing it
1082	 * from any future interrupt callback.  A will then wait on C before
1083	 * executing (if present).
1084	 *
1085	 * As B is second, it sees A as the previous fence and so waits for
1086	 * it to complete its transition and takes over the occupancy for
1087	 * itself -- remembering that it needs to wait on A before executing.
1088	 */
1089	if (prev) {
1090		__list_del_entry(&active->cb.node);
1091		spin_unlock(prev->lock); /* serialise with prev->cb_list */
1092	}
1093	list_add_tail(&active->cb.node, &fence->cb_list);
1094	spin_unlock_irqrestore(fence->lock, flags);
1095
1096	return prev;
1097}
1098
1099int i915_active_fence_set(struct i915_active_fence *active,
1100			  struct i915_request *rq)
1101{
1102	struct dma_fence *fence;
1103	int err = 0;
1104
1105	/* Must maintain timeline ordering wrt previous active requests */
1106	fence = __i915_active_fence_set(active, &rq->fence);
1107	if (fence) {
1108		err = i915_request_await_dma_fence(rq, fence);
1109		dma_fence_put(fence);
1110	}
1111
1112	return err;
1113}
1114
1115void i915_active_noop(struct dma_fence *fence, struct dma_fence_cb *cb)
1116{
1117	active_fence_cb(fence, cb);
1118}
1119
1120struct auto_active {
1121	struct i915_active base;
1122	struct kref ref;
1123};
1124
1125struct i915_active *i915_active_get(struct i915_active *ref)
1126{
1127	struct auto_active *aa = container_of(ref, typeof(*aa), base);
1128
1129	kref_get(&aa->ref);
1130	return &aa->base;
1131}
1132
1133static void auto_release(struct kref *ref)
1134{
1135	struct auto_active *aa = container_of(ref, typeof(*aa), ref);
1136
1137	i915_active_fini(&aa->base);
1138	kfree(aa);
1139}
1140
1141void i915_active_put(struct i915_active *ref)
1142{
1143	struct auto_active *aa = container_of(ref, typeof(*aa), base);
1144
1145	kref_put(&aa->ref, auto_release);
1146}
1147
1148static int auto_active(struct i915_active *ref)
1149{
1150	i915_active_get(ref);
1151	return 0;
1152}
1153
1154static void auto_retire(struct i915_active *ref)
1155{
1156	i915_active_put(ref);
1157}
1158
1159struct i915_active *i915_active_create(void)
1160{
1161	struct auto_active *aa;
1162
1163	aa = kmalloc(sizeof(*aa), GFP_KERNEL);
1164	if (!aa)
1165		return NULL;
1166
1167	kref_init(&aa->ref);
1168	i915_active_init(&aa->base, auto_active, auto_retire, 0);
1169
1170	return &aa->base;
1171}
1172
1173#if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
1174#include "selftests/i915_active.c"
1175#endif
1176
1177void i915_active_module_exit(void)
1178{
1179	kmem_cache_destroy(slab_cache);
1180}
1181
1182int __init i915_active_module_init(void)
1183{
1184	slab_cache = KMEM_CACHE(active_node, SLAB_HWCACHE_ALIGN);
1185	if (!slab_cache)
1186		return -ENOMEM;
1187
1188	return 0;
1189}