memalloc.c

   1// SPDX-License-Identifier: GPL-2.0-only
   2/* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */
   3#include <linux/mm.h>
   4#include <linux/llist.h>
   5#include <linux/bpf.h>
   6#include <linux/irq_work.h>
   7#include <linux/bpf_mem_alloc.h>
   8#include <linux/memcontrol.h>
   9#include <asm/local.h>
  10
  11/* Any context (including NMI) BPF specific memory allocator.
  12 *
  13 * Tracing BPF programs can attach to kprobe and fentry. Hence they
  14 * run in unknown context where calling plain kmalloc() might not be safe.
  15 *
  16 * Front-end kmalloc() with per-cpu per-bucket cache of free elements.
  17 * Refill this cache asynchronously from irq_work.
  18 *
  19 * CPU_0 buckets
  20 * 16 32 64 96 128 196 256 512 1024 2048 4096
  21 * ...
  22 * CPU_N buckets
  23 * 16 32 64 96 128 196 256 512 1024 2048 4096
  24 *
  25 * The buckets are prefilled at the start.
  26 * BPF programs always run with migration disabled.
  27 * It's safe to allocate from cache of the current cpu with irqs disabled.
  28 * Free-ing is always done into bucket of the current cpu as well.
  29 * irq_work trims extra free elements from buckets with kfree
  30 * and refills them with kmalloc, so global kmalloc logic takes care
  31 * of freeing objects allocated by one cpu and freed on another.
  32 *
  33 * Every allocated objected is padded with extra 8 bytes that contains
  34 * struct llist_node.
  35 */
  36#define LLIST_NODE_SZ sizeof(struct llist_node)
  37
  38#define BPF_MEM_ALLOC_SIZE_MAX 4096
  39
  40/* similar to kmalloc, but sizeof == 8 bucket is gone */
  41static u8 size_index[24] __ro_after_init = {
  42	3,	/* 8 */
  43	3,	/* 16 */
  44	4,	/* 24 */
  45	4,	/* 32 */
  46	5,	/* 40 */
  47	5,	/* 48 */
  48	5,	/* 56 */
  49	5,	/* 64 */
  50	1,	/* 72 */
  51	1,	/* 80 */
  52	1,	/* 88 */
  53	1,	/* 96 */
  54	6,	/* 104 */
  55	6,	/* 112 */
  56	6,	/* 120 */
  57	6,	/* 128 */
  58	2,	/* 136 */
  59	2,	/* 144 */
  60	2,	/* 152 */
  61	2,	/* 160 */
  62	2,	/* 168 */
  63	2,	/* 176 */
  64	2,	/* 184 */
  65	2	/* 192 */
  66};
  67
  68static int bpf_mem_cache_idx(size_t size)
  69{
  70	if (!size || size > BPF_MEM_ALLOC_SIZE_MAX)
  71		return -1;
  72
  73	if (size <= 192)
  74		return size_index[(size - 1) / 8] - 1;
  75
  76	return fls(size - 1) - 2;
  77}
  78
  79#define NUM_CACHES 11
  80
  81struct bpf_mem_cache {
  82	/* per-cpu list of free objects of size 'unit_size'.
  83	 * All accesses are done with interrupts disabled and 'active' counter
  84	 * protection with __llist_add() and __llist_del_first().
  85	 */
  86	struct llist_head free_llist;
  87	local_t active;
  88
  89	/* Operations on the free_list from unit_alloc/unit_free/bpf_mem_refill
  90	 * are sequenced by per-cpu 'active' counter. But unit_free() cannot
  91	 * fail. When 'active' is busy the unit_free() will add an object to
  92	 * free_llist_extra.
  93	 */
  94	struct llist_head free_llist_extra;
  95
  96	struct irq_work refill_work;
  97	struct obj_cgroup *objcg;
  98	int unit_size;
  99	/* count of objects in free_llist */
 100	int free_cnt;
 101	int low_watermark, high_watermark, batch;
 102	int percpu_size;
 103	bool draining;
 104	struct bpf_mem_cache *tgt;
 105
 106	/* list of objects to be freed after RCU GP */
 107	struct llist_head free_by_rcu;
 108	struct llist_node *free_by_rcu_tail;
 109	struct llist_head waiting_for_gp;
 110	struct llist_node *waiting_for_gp_tail;
 111	struct rcu_head rcu;
 112	atomic_t call_rcu_in_progress;
 113	struct llist_head free_llist_extra_rcu;
 114
 115	/* list of objects to be freed after RCU tasks trace GP */
 116	struct llist_head free_by_rcu_ttrace;
 117	struct llist_head waiting_for_gp_ttrace;
 118	struct rcu_head rcu_ttrace;
 119	atomic_t call_rcu_ttrace_in_progress;
 120};
 121
 122struct bpf_mem_caches {
 123	struct bpf_mem_cache cache[NUM_CACHES];
 124};
 125
 126static const u16 sizes[NUM_CACHES] = {96, 192, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096};
 127
 128static struct llist_node notrace *__llist_del_first(struct llist_head *head)
 129{
 130	struct llist_node *entry, *next;
 131
 132	entry = head->first;
 133	if (!entry)
 134		return NULL;
 135	next = entry->next;
 136	head->first = next;
 137	return entry;
 138}
 139
 140static void *__alloc(struct bpf_mem_cache *c, int node, gfp_t flags)
 141{
 142	if (c->percpu_size) {
 143		void __percpu **obj = kmalloc_node(c->percpu_size, flags, node);
 144		void __percpu *pptr = __alloc_percpu_gfp(c->unit_size, 8, flags);
 145
 146		if (!obj || !pptr) {
 147			free_percpu(pptr);
 148			kfree(obj);
 149			return NULL;
 150		}
 151		obj[1] = pptr;
 152		return obj;
 153	}
 154
 155	return kmalloc_node(c->unit_size, flags | __GFP_ZERO, node);
 156}
 157
 158static struct mem_cgroup *get_memcg(const struct bpf_mem_cache *c)
 159{
 160#ifdef CONFIG_MEMCG
 161	if (c->objcg)
 162		return get_mem_cgroup_from_objcg(c->objcg);
 163	return root_mem_cgroup;
 164#else
 165	return NULL;
 166#endif
 167}
 168
 169static void inc_active(struct bpf_mem_cache *c, unsigned long *flags)
 170{
 171	if (IS_ENABLED(CONFIG_PREEMPT_RT))
 172		/* In RT irq_work runs in per-cpu kthread, so disable
 173		 * interrupts to avoid preemption and interrupts and
 174		 * reduce the chance of bpf prog executing on this cpu
 175		 * when active counter is busy.
 176		 */
 177		local_irq_save(*flags);
 178	/* alloc_bulk runs from irq_work which will not preempt a bpf
 179	 * program that does unit_alloc/unit_free since IRQs are
 180	 * disabled there. There is no race to increment 'active'
 181	 * counter. It protects free_llist from corruption in case NMI
 182	 * bpf prog preempted this loop.
 183	 */
 184	WARN_ON_ONCE(local_inc_return(&c->active) != 1);
 185}
 186
 187static void dec_active(struct bpf_mem_cache *c, unsigned long *flags)
 188{
 189	local_dec(&c->active);
 190	if (IS_ENABLED(CONFIG_PREEMPT_RT))
 191		local_irq_restore(*flags);
 192}
 193
 194static void add_obj_to_free_list(struct bpf_mem_cache *c, void *obj)
 195{
 196	unsigned long flags;
 197
 198	inc_active(c, &flags);
 199	__llist_add(obj, &c->free_llist);
 200	c->free_cnt++;
 201	dec_active(c, &flags);
 202}
 203
 204/* Mostly runs from irq_work except __init phase. */
 205static void alloc_bulk(struct bpf_mem_cache *c, int cnt, int node, bool atomic)
 206{
 207	struct mem_cgroup *memcg = NULL, *old_memcg;
 208	gfp_t gfp;
 209	void *obj;
 210	int i;
 211
 212	gfp = __GFP_NOWARN | __GFP_ACCOUNT;
 213	gfp |= atomic ? GFP_NOWAIT : GFP_KERNEL;
 214
 215	for (i = 0; i < cnt; i++) {
 216		/*
 217		 * For every 'c' llist_del_first(&c->free_by_rcu_ttrace); is
 218		 * done only by one CPU == current CPU. Other CPUs might
 219		 * llist_add() and llist_del_all() in parallel.
 220		 */
 221		obj = llist_del_first(&c->free_by_rcu_ttrace);
 222		if (!obj)
 223			break;
 224		add_obj_to_free_list(c, obj);
 225	}
 226	if (i >= cnt)
 227		return;
 228
 229	for (; i < cnt; i++) {
 230		obj = llist_del_first(&c->waiting_for_gp_ttrace);
 231		if (!obj)
 232			break;
 233		add_obj_to_free_list(c, obj);
 234	}
 235	if (i >= cnt)
 236		return;
 237
 238	memcg = get_memcg(c);
 239	old_memcg = set_active_memcg(memcg);
 240	for (; i < cnt; i++) {
 241		/* Allocate, but don't deplete atomic reserves that typical
 242		 * GFP_ATOMIC would do. irq_work runs on this cpu and kmalloc
 243		 * will allocate from the current numa node which is what we
 244		 * want here.
 245		 */
 246		obj = __alloc(c, node, gfp);
 247		if (!obj)
 248			break;
 249		add_obj_to_free_list(c, obj);
 250	}
 251	set_active_memcg(old_memcg);
 252	mem_cgroup_put(memcg);
 253}
 254
 255static void free_one(void *obj, bool percpu)
 256{
 257	if (percpu)
 258		free_percpu(((void __percpu **)obj)[1]);
 259
 260	kfree(obj);
 261}
 262
 263static int free_all(struct llist_node *llnode, bool percpu)
 264{
 265	struct llist_node *pos, *t;
 266	int cnt = 0;
 267
 268	llist_for_each_safe(pos, t, llnode) {
 269		free_one(pos, percpu);
 270		cnt++;
 271	}
 272	return cnt;
 273}
 274
 275static void __free_rcu(struct rcu_head *head)
 276{
 277	struct bpf_mem_cache *c = container_of(head, struct bpf_mem_cache, rcu_ttrace);
 278
 279	free_all(llist_del_all(&c->waiting_for_gp_ttrace), !!c->percpu_size);
 280	atomic_set(&c->call_rcu_ttrace_in_progress, 0);
 281}
 282
 283static void __free_rcu_tasks_trace(struct rcu_head *head)
 284{
 285	/* If RCU Tasks Trace grace period implies RCU grace period,
 286	 * there is no need to invoke call_rcu().
 287	 */
 288	if (rcu_trace_implies_rcu_gp())
 289		__free_rcu(head);
 290	else
 291		call_rcu(head, __free_rcu);
 292}
 293
 294static void enque_to_free(struct bpf_mem_cache *c, void *obj)
 295{
 296	struct llist_node *llnode = obj;
 297
 298	/* bpf_mem_cache is a per-cpu object. Freeing happens in irq_work.
 299	 * Nothing races to add to free_by_rcu_ttrace list.
 300	 */
 301	llist_add(llnode, &c->free_by_rcu_ttrace);
 302}
 303
 304static void do_call_rcu_ttrace(struct bpf_mem_cache *c)
 305{
 306	struct llist_node *llnode, *t;
 307
 308	if (atomic_xchg(&c->call_rcu_ttrace_in_progress, 1)) {
 309		if (unlikely(READ_ONCE(c->draining))) {
 310			llnode = llist_del_all(&c->free_by_rcu_ttrace);
 311			free_all(llnode, !!c->percpu_size);
 312		}
 313		return;
 314	}
 315
 316	WARN_ON_ONCE(!llist_empty(&c->waiting_for_gp_ttrace));
 317	llist_for_each_safe(llnode, t, llist_del_all(&c->free_by_rcu_ttrace))
 318		llist_add(llnode, &c->waiting_for_gp_ttrace);
 319
 320	if (unlikely(READ_ONCE(c->draining))) {
 321		__free_rcu(&c->rcu_ttrace);
 322		return;
 323	}
 324
 325	/* Use call_rcu_tasks_trace() to wait for sleepable progs to finish.
 326	 * If RCU Tasks Trace grace period implies RCU grace period, free
 327	 * these elements directly, else use call_rcu() to wait for normal
 328	 * progs to finish and finally do free_one() on each element.
 329	 */
 330	call_rcu_tasks_trace(&c->rcu_ttrace, __free_rcu_tasks_trace);
 331}
 332
 333static void free_bulk(struct bpf_mem_cache *c)
 334{
 335	struct bpf_mem_cache *tgt = c->tgt;
 336	struct llist_node *llnode, *t;
 337	unsigned long flags;
 338	int cnt;
 339
 340	WARN_ON_ONCE(tgt->unit_size != c->unit_size);
 341	WARN_ON_ONCE(tgt->percpu_size != c->percpu_size);
 342
 343	do {
 344		inc_active(c, &flags);
 345		llnode = __llist_del_first(&c->free_llist);
 346		if (llnode)
 347			cnt = --c->free_cnt;
 348		else
 349			cnt = 0;
 350		dec_active(c, &flags);
 351		if (llnode)
 352			enque_to_free(tgt, llnode);
 353	} while (cnt > (c->high_watermark + c->low_watermark) / 2);
 354
 355	/* and drain free_llist_extra */
 356	llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist_extra))
 357		enque_to_free(tgt, llnode);
 358	do_call_rcu_ttrace(tgt);
 359}
 360
 361static void __free_by_rcu(struct rcu_head *head)
 362{
 363	struct bpf_mem_cache *c = container_of(head, struct bpf_mem_cache, rcu);
 364	struct bpf_mem_cache *tgt = c->tgt;
 365	struct llist_node *llnode;
 366
 367	WARN_ON_ONCE(tgt->unit_size != c->unit_size);
 368	WARN_ON_ONCE(tgt->percpu_size != c->percpu_size);
 369
 370	llnode = llist_del_all(&c->waiting_for_gp);
 371	if (!llnode)
 372		goto out;
 373
 374	llist_add_batch(llnode, c->waiting_for_gp_tail, &tgt->free_by_rcu_ttrace);
 375
 376	/* Objects went through regular RCU GP. Send them to RCU tasks trace */
 377	do_call_rcu_ttrace(tgt);
 378out:
 379	atomic_set(&c->call_rcu_in_progress, 0);
 380}
 381
 382static void check_free_by_rcu(struct bpf_mem_cache *c)
 383{
 384	struct llist_node *llnode, *t;
 385	unsigned long flags;
 386
 387	/* drain free_llist_extra_rcu */
 388	if (unlikely(!llist_empty(&c->free_llist_extra_rcu))) {
 389		inc_active(c, &flags);
 390		llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist_extra_rcu))
 391			if (__llist_add(llnode, &c->free_by_rcu))
 392				c->free_by_rcu_tail = llnode;
 393		dec_active(c, &flags);
 394	}
 395
 396	if (llist_empty(&c->free_by_rcu))
 397		return;
 398
 399	if (atomic_xchg(&c->call_rcu_in_progress, 1)) {
 400		/*
 401		 * Instead of kmalloc-ing new rcu_head and triggering 10k
 402		 * call_rcu() to hit rcutree.qhimark and force RCU to notice
 403		 * the overload just ask RCU to hurry up. There could be many
 404		 * objects in free_by_rcu list.
 405		 * This hint reduces memory consumption for an artificial
 406		 * benchmark from 2 Gbyte to 150 Mbyte.
 407		 */
 408		rcu_request_urgent_qs_task(current);
 409		return;
 410	}
 411
 412	WARN_ON_ONCE(!llist_empty(&c->waiting_for_gp));
 413
 414	inc_active(c, &flags);
 415	WRITE_ONCE(c->waiting_for_gp.first, __llist_del_all(&c->free_by_rcu));
 416	c->waiting_for_gp_tail = c->free_by_rcu_tail;
 417	dec_active(c, &flags);
 418
 419	if (unlikely(READ_ONCE(c->draining))) {
 420		free_all(llist_del_all(&c->waiting_for_gp), !!c->percpu_size);
 421		atomic_set(&c->call_rcu_in_progress, 0);
 422	} else {
 423		call_rcu_hurry(&c->rcu, __free_by_rcu);
 424	}
 425}
 426
 427static void bpf_mem_refill(struct irq_work *work)
 428{
 429	struct bpf_mem_cache *c = container_of(work, struct bpf_mem_cache, refill_work);
 430	int cnt;
 431
 432	/* Racy access to free_cnt. It doesn't need to be 100% accurate */
 433	cnt = c->free_cnt;
 434	if (cnt < c->low_watermark)
 435		/* irq_work runs on this cpu and kmalloc will allocate
 436		 * from the current numa node which is what we want here.
 437		 */
 438		alloc_bulk(c, c->batch, NUMA_NO_NODE, true);
 439	else if (cnt > c->high_watermark)
 440		free_bulk(c);
 441
 442	check_free_by_rcu(c);
 443}
 444
 445static void notrace irq_work_raise(struct bpf_mem_cache *c)
 446{
 447	irq_work_queue(&c->refill_work);
 448}
 449
 450/* For typical bpf map case that uses bpf_mem_cache_alloc and single bucket
 451 * the freelist cache will be elem_size * 64 (or less) on each cpu.
 452 *
 453 * For bpf programs that don't have statically known allocation sizes and
 454 * assuming (low_mark + high_mark) / 2 as an average number of elements per
 455 * bucket and all buckets are used the total amount of memory in freelists
 456 * on each cpu will be:
 457 * 64*16 + 64*32 + 64*64 + 64*96 + 64*128 + 64*196 + 64*256 + 32*512 + 16*1024 + 8*2048 + 4*4096
 458 * == ~ 116 Kbyte using below heuristic.
 459 * Initialized, but unused bpf allocator (not bpf map specific one) will
 460 * consume ~ 11 Kbyte per cpu.
 461 * Typical case will be between 11K and 116K closer to 11K.
 462 * bpf progs can and should share bpf_mem_cache when possible.
 463 *
 464 * Percpu allocation is typically rare. To avoid potential unnecessary large
 465 * memory consumption, set low_mark = 1 and high_mark = 3, resulting in c->batch = 1.
 466 */
 467static void init_refill_work(struct bpf_mem_cache *c)
 468{
 469	init_irq_work(&c->refill_work, bpf_mem_refill);
 470	if (c->percpu_size) {
 471		c->low_watermark = 1;
 472		c->high_watermark = 3;
 473	} else if (c->unit_size <= 256) {
 474		c->low_watermark = 32;
 475		c->high_watermark = 96;
 476	} else {
 477		/* When page_size == 4k, order-0 cache will have low_mark == 2
 478		 * and high_mark == 6 with batch alloc of 3 individual pages at
 479		 * a time.
 480		 * 8k allocs and above low == 1, high == 3, batch == 1.
 481		 */
 482		c->low_watermark = max(32 * 256 / c->unit_size, 1);
 483		c->high_watermark = max(96 * 256 / c->unit_size, 3);
 484	}
 485	c->batch = max((c->high_watermark - c->low_watermark) / 4 * 3, 1);
 486}
 487
 488static void prefill_mem_cache(struct bpf_mem_cache *c, int cpu)
 489{
 490	int cnt = 1;
 491
 492	/* To avoid consuming memory, for non-percpu allocation, assume that
 493	 * 1st run of bpf prog won't be doing more than 4 map_update_elem from
 494	 * irq disabled region if unit size is less than or equal to 256.
 495	 * For all other cases, let us just do one allocation.
 496	 */
 497	if (!c->percpu_size && c->unit_size <= 256)
 498		cnt = 4;
 499	alloc_bulk(c, cnt, cpu_to_node(cpu), false);
 500}
 501
 502/* When size != 0 bpf_mem_cache for each cpu.
 503 * This is typical bpf hash map use case when all elements have equal size.
 504 *
 505 * When size == 0 allocate 11 bpf_mem_cache-s for each cpu, then rely on
 506 * kmalloc/kfree. Max allocation size is 4096 in this case.
 507 * This is bpf_dynptr and bpf_kptr use case.
 508 */
 509int bpf_mem_alloc_init(struct bpf_mem_alloc *ma, int size, bool percpu)
 510{
 511	struct bpf_mem_caches *cc; struct bpf_mem_caches __percpu *pcc;
 512	struct bpf_mem_cache *c; struct bpf_mem_cache __percpu *pc;
 513	struct obj_cgroup *objcg = NULL;
 514	int cpu, i, unit_size, percpu_size = 0;
 515
 516	if (percpu && size == 0)
 517		return -EINVAL;
 518
 519	/* room for llist_node and per-cpu pointer */
 520	if (percpu)
 521		percpu_size = LLIST_NODE_SZ + sizeof(void *);
 522	ma->percpu = percpu;
 523
 524	if (size) {
 525		pc = __alloc_percpu_gfp(sizeof(*pc), 8, GFP_KERNEL);
 526		if (!pc)
 527			return -ENOMEM;
 528
 529		if (!percpu)
 530			size += LLIST_NODE_SZ; /* room for llist_node */
 531		unit_size = size;
 532
 533#ifdef CONFIG_MEMCG
 534		if (memcg_bpf_enabled())
 535			objcg = get_obj_cgroup_from_current();
 536#endif
 537		ma->objcg = objcg;
 538
 539		for_each_possible_cpu(cpu) {
 540			c = per_cpu_ptr(pc, cpu);
 541			c->unit_size = unit_size;
 542			c->objcg = objcg;
 543			c->percpu_size = percpu_size;
 544			c->tgt = c;
 545			init_refill_work(c);
 546			prefill_mem_cache(c, cpu);
 547		}
 548		ma->cache = pc;
 549		return 0;
 550	}
 551
 552	pcc = __alloc_percpu_gfp(sizeof(*cc), 8, GFP_KERNEL);
 553	if (!pcc)
 554		return -ENOMEM;
 555#ifdef CONFIG_MEMCG
 556	objcg = get_obj_cgroup_from_current();
 557#endif
 558	ma->objcg = objcg;
 559	for_each_possible_cpu(cpu) {
 560		cc = per_cpu_ptr(pcc, cpu);
 561		for (i = 0; i < NUM_CACHES; i++) {
 562			c = &cc->cache[i];
 563			c->unit_size = sizes[i];
 564			c->objcg = objcg;
 565			c->percpu_size = percpu_size;
 566			c->tgt = c;
 567
 568			init_refill_work(c);
 569			prefill_mem_cache(c, cpu);
 570		}
 571	}
 572
 573	ma->caches = pcc;
 574	return 0;
 575}
 576
 577int bpf_mem_alloc_percpu_init(struct bpf_mem_alloc *ma, struct obj_cgroup *objcg)
 578{
 579	struct bpf_mem_caches __percpu *pcc;
 580
 581	pcc = __alloc_percpu_gfp(sizeof(struct bpf_mem_caches), 8, GFP_KERNEL);
 582	if (!pcc)
 583		return -ENOMEM;
 584
 585	ma->caches = pcc;
 586	ma->objcg = objcg;
 587	ma->percpu = true;
 588	return 0;
 589}
 590
 591int bpf_mem_alloc_percpu_unit_init(struct bpf_mem_alloc *ma, int size)
 592{
 593	struct bpf_mem_caches *cc; struct bpf_mem_caches __percpu *pcc;
 594	int cpu, i, unit_size, percpu_size;
 595	struct obj_cgroup *objcg;
 596	struct bpf_mem_cache *c;
 597
 598	i = bpf_mem_cache_idx(size);
 599	if (i < 0)
 600		return -EINVAL;
 601
 602	/* room for llist_node and per-cpu pointer */
 603	percpu_size = LLIST_NODE_SZ + sizeof(void *);
 604
 605	unit_size = sizes[i];
 606	objcg = ma->objcg;
 607	pcc = ma->caches;
 608
 609	for_each_possible_cpu(cpu) {
 610		cc = per_cpu_ptr(pcc, cpu);
 611		c = &cc->cache[i];
 612		if (c->unit_size)
 613			break;
 614
 615		c->unit_size = unit_size;
 616		c->objcg = objcg;
 617		c->percpu_size = percpu_size;
 618		c->tgt = c;
 619
 620		init_refill_work(c);
 621		prefill_mem_cache(c, cpu);
 622	}
 623
 624	return 0;
 625}
 626
 627static void drain_mem_cache(struct bpf_mem_cache *c)
 628{
 629	bool percpu = !!c->percpu_size;
 630
 631	/* No progs are using this bpf_mem_cache, but htab_map_free() called
 632	 * bpf_mem_cache_free() for all remaining elements and they can be in
 633	 * free_by_rcu_ttrace or in waiting_for_gp_ttrace lists, so drain those lists now.
 634	 *
 635	 * Except for waiting_for_gp_ttrace list, there are no concurrent operations
 636	 * on these lists, so it is safe to use __llist_del_all().
 637	 */
 638	free_all(llist_del_all(&c->free_by_rcu_ttrace), percpu);
 639	free_all(llist_del_all(&c->waiting_for_gp_ttrace), percpu);
 640	free_all(__llist_del_all(&c->free_llist), percpu);
 641	free_all(__llist_del_all(&c->free_llist_extra), percpu);
 642	free_all(__llist_del_all(&c->free_by_rcu), percpu);
 643	free_all(__llist_del_all(&c->free_llist_extra_rcu), percpu);
 644	free_all(llist_del_all(&c->waiting_for_gp), percpu);
 645}
 646
 647static void check_mem_cache(struct bpf_mem_cache *c)
 648{
 649	WARN_ON_ONCE(!llist_empty(&c->free_by_rcu_ttrace));
 650	WARN_ON_ONCE(!llist_empty(&c->waiting_for_gp_ttrace));
 651	WARN_ON_ONCE(!llist_empty(&c->free_llist));
 652	WARN_ON_ONCE(!llist_empty(&c->free_llist_extra));
 653	WARN_ON_ONCE(!llist_empty(&c->free_by_rcu));
 654	WARN_ON_ONCE(!llist_empty(&c->free_llist_extra_rcu));
 655	WARN_ON_ONCE(!llist_empty(&c->waiting_for_gp));
 656}
 657
 658static void check_leaked_objs(struct bpf_mem_alloc *ma)
 659{
 660	struct bpf_mem_caches *cc;
 661	struct bpf_mem_cache *c;
 662	int cpu, i;
 663
 664	if (ma->cache) {
 665		for_each_possible_cpu(cpu) {
 666			c = per_cpu_ptr(ma->cache, cpu);
 667			check_mem_cache(c);
 668		}
 669	}
 670	if (ma->caches) {
 671		for_each_possible_cpu(cpu) {
 672			cc = per_cpu_ptr(ma->caches, cpu);
 673			for (i = 0; i < NUM_CACHES; i++) {
 674				c = &cc->cache[i];
 675				check_mem_cache(c);
 676			}
 677		}
 678	}
 679}
 680
 681static void free_mem_alloc_no_barrier(struct bpf_mem_alloc *ma)
 682{
 683	check_leaked_objs(ma);
 684	free_percpu(ma->cache);
 685	free_percpu(ma->caches);
 686	ma->cache = NULL;
 687	ma->caches = NULL;
 688}
 689
 690static void free_mem_alloc(struct bpf_mem_alloc *ma)
 691{
 692	/* waiting_for_gp[_ttrace] lists were drained, but RCU callbacks
 693	 * might still execute. Wait for them.
 694	 *
 695	 * rcu_barrier_tasks_trace() doesn't imply synchronize_rcu_tasks_trace(),
 696	 * but rcu_barrier_tasks_trace() and rcu_barrier() below are only used
 697	 * to wait for the pending __free_rcu_tasks_trace() and __free_rcu(),
 698	 * so if call_rcu(head, __free_rcu) is skipped due to
 699	 * rcu_trace_implies_rcu_gp(), it will be OK to skip rcu_barrier() by
 700	 * using rcu_trace_implies_rcu_gp() as well.
 701	 */
 702	rcu_barrier(); /* wait for __free_by_rcu */
 703	rcu_barrier_tasks_trace(); /* wait for __free_rcu */
 704	if (!rcu_trace_implies_rcu_gp())
 705		rcu_barrier();
 706	free_mem_alloc_no_barrier(ma);
 707}
 708
 709static void free_mem_alloc_deferred(struct work_struct *work)
 710{
 711	struct bpf_mem_alloc *ma = container_of(work, struct bpf_mem_alloc, work);
 712
 713	free_mem_alloc(ma);
 714	kfree(ma);
 715}
 716
 717static void destroy_mem_alloc(struct bpf_mem_alloc *ma, int rcu_in_progress)
 718{
 719	struct bpf_mem_alloc *copy;
 720
 721	if (!rcu_in_progress) {
 722		/* Fast path. No callbacks are pending, hence no need to do
 723		 * rcu_barrier-s.
 724		 */
 725		free_mem_alloc_no_barrier(ma);
 726		return;
 727	}
 728
 729	copy = kmemdup(ma, sizeof(*ma), GFP_KERNEL);
 730	if (!copy) {
 731		/* Slow path with inline barrier-s */
 732		free_mem_alloc(ma);
 733		return;
 734	}
 735
 736	/* Defer barriers into worker to let the rest of map memory to be freed */
 737	memset(ma, 0, sizeof(*ma));
 738	INIT_WORK(&copy->work, free_mem_alloc_deferred);
 739	queue_work(system_dfl_wq, &copy->work);
 740}
 741
 742void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma)
 743{
 744	struct bpf_mem_caches *cc;
 745	struct bpf_mem_cache *c;
 746	int cpu, i, rcu_in_progress;
 747
 748	if (ma->cache) {
 749		rcu_in_progress = 0;
 750		for_each_possible_cpu(cpu) {
 751			c = per_cpu_ptr(ma->cache, cpu);
 752			WRITE_ONCE(c->draining, true);
 753			irq_work_sync(&c->refill_work);
 754			drain_mem_cache(c);
 755			rcu_in_progress += atomic_read(&c->call_rcu_ttrace_in_progress);
 756			rcu_in_progress += atomic_read(&c->call_rcu_in_progress);
 757		}
 758		obj_cgroup_put(ma->objcg);
 759		destroy_mem_alloc(ma, rcu_in_progress);
 760	}
 761	if (ma->caches) {
 762		rcu_in_progress = 0;
 763		for_each_possible_cpu(cpu) {
 764			cc = per_cpu_ptr(ma->caches, cpu);
 765			for (i = 0; i < NUM_CACHES; i++) {
 766				c = &cc->cache[i];
 767				WRITE_ONCE(c->draining, true);
 768				irq_work_sync(&c->refill_work);
 769				drain_mem_cache(c);
 770				rcu_in_progress += atomic_read(&c->call_rcu_ttrace_in_progress);
 771				rcu_in_progress += atomic_read(&c->call_rcu_in_progress);
 772			}
 773		}
 774		obj_cgroup_put(ma->objcg);
 775		destroy_mem_alloc(ma, rcu_in_progress);
 776	}
 777}
 778
 779/* notrace is necessary here and in other functions to make sure
 780 * bpf programs cannot attach to them and cause llist corruptions.
 781 */
 782static void notrace *unit_alloc(struct bpf_mem_cache *c)
 783{
 784	struct llist_node *llnode = NULL;
 785	unsigned long flags;
 786	int cnt = 0;
 787
 788	/* Disable irqs to prevent the following race for majority of prog types:
 789	 * prog_A
 790	 *   bpf_mem_alloc
 791	 *      preemption or irq -> prog_B
 792	 *        bpf_mem_alloc
 793	 *
 794	 * but prog_B could be a perf_event NMI prog.
 795	 * Use per-cpu 'active' counter to order free_list access between
 796	 * unit_alloc/unit_free/bpf_mem_refill.
 797	 */
 798	local_irq_save(flags);
 799	if (local_inc_return(&c->active) == 1) {
 800		llnode = __llist_del_first(&c->free_llist);
 801		if (llnode) {
 802			cnt = --c->free_cnt;
 803			*(struct bpf_mem_cache **)llnode = c;
 804		}
 805	}
 806	local_dec(&c->active);
 807
 808	WARN_ON(cnt < 0);
 809
 810	if (cnt < c->low_watermark)
 811		irq_work_raise(c);
 812	/* Enable IRQ after the enqueue of irq work completes, so irq work
 813	 * will run after IRQ is enabled and free_llist may be refilled by
 814	 * irq work before other task preempts current task.
 815	 */
 816	local_irq_restore(flags);
 817
 818	return llnode;
 819}
 820
 821/* Though 'ptr' object could have been allocated on a different cpu
 822 * add it to the free_llist of the current cpu.
 823 * Let kfree() logic deal with it when it's later called from irq_work.
 824 */
 825static void notrace unit_free(struct bpf_mem_cache *c, void *ptr)
 826{
 827	struct llist_node *llnode = ptr - LLIST_NODE_SZ;
 828	unsigned long flags;
 829	int cnt = 0;
 830
 831	BUILD_BUG_ON(LLIST_NODE_SZ > 8);
 832
 833	/*
 834	 * Remember bpf_mem_cache that allocated this object.
 835	 * The hint is not accurate.
 836	 */
 837	c->tgt = *(struct bpf_mem_cache **)llnode;
 838
 839	local_irq_save(flags);
 840	if (local_inc_return(&c->active) == 1) {
 841		__llist_add(llnode, &c->free_llist);
 842		cnt = ++c->free_cnt;
 843	} else {
 844		/* unit_free() cannot fail. Therefore add an object to atomic
 845		 * llist. free_bulk() will drain it. Though free_llist_extra is
 846		 * a per-cpu list we have to use atomic llist_add here, since
 847		 * it also can be interrupted by bpf nmi prog that does another
 848		 * unit_free() into the same free_llist_extra.
 849		 */
 850		llist_add(llnode, &c->free_llist_extra);
 851	}
 852	local_dec(&c->active);
 853
 854	if (cnt > c->high_watermark)
 855		/* free few objects from current cpu into global kmalloc pool */
 856		irq_work_raise(c);
 857	/* Enable IRQ after irq_work_raise() completes, otherwise when current
 858	 * task is preempted by task which does unit_alloc(), unit_alloc() may
 859	 * return NULL unexpectedly because irq work is already pending but can
 860	 * not been triggered and free_llist can not be refilled timely.
 861	 */
 862	local_irq_restore(flags);
 863}
 864
 865static void notrace unit_free_rcu(struct bpf_mem_cache *c, void *ptr)
 866{
 867	struct llist_node *llnode = ptr - LLIST_NODE_SZ;
 868	unsigned long flags;
 869
 870	c->tgt = *(struct bpf_mem_cache **)llnode;
 871
 872	local_irq_save(flags);
 873	if (local_inc_return(&c->active) == 1) {
 874		if (__llist_add(llnode, &c->free_by_rcu))
 875			c->free_by_rcu_tail = llnode;
 876	} else {
 877		llist_add(llnode, &c->free_llist_extra_rcu);
 878	}
 879	local_dec(&c->active);
 880
 881	if (!atomic_read(&c->call_rcu_in_progress))
 882		irq_work_raise(c);
 883	local_irq_restore(flags);
 884}
 885
 886/* Called from BPF program or from sys_bpf syscall.
 887 * In both cases migration is disabled.
 888 */
 889void notrace *bpf_mem_alloc(struct bpf_mem_alloc *ma, size_t size)
 890{
 891	int idx;
 892	void *ret;
 893
 894	if (!size)
 895		return NULL;
 896
 897	if (!ma->percpu)
 898		size += LLIST_NODE_SZ;
 899	idx = bpf_mem_cache_idx(size);
 900	if (idx < 0)
 901		return NULL;
 902
 903	ret = unit_alloc(this_cpu_ptr(ma->caches)->cache + idx);
 904	return !ret ? NULL : ret + LLIST_NODE_SZ;
 905}
 906
 907void notrace bpf_mem_free(struct bpf_mem_alloc *ma, void *ptr)
 908{
 909	struct bpf_mem_cache *c;
 910	int idx;
 911
 912	if (!ptr)
 913		return;
 914
 915	c = *(void **)(ptr - LLIST_NODE_SZ);
 916	idx = bpf_mem_cache_idx(c->unit_size);
 917	if (WARN_ON_ONCE(idx < 0))
 918		return;
 919
 920	unit_free(this_cpu_ptr(ma->caches)->cache + idx, ptr);
 921}
 922
 923void notrace bpf_mem_free_rcu(struct bpf_mem_alloc *ma, void *ptr)
 924{
 925	struct bpf_mem_cache *c;
 926	int idx;
 927
 928	if (!ptr)
 929		return;
 930
 931	c = *(void **)(ptr - LLIST_NODE_SZ);
 932	idx = bpf_mem_cache_idx(c->unit_size);
 933	if (WARN_ON_ONCE(idx < 0))
 934		return;
 935
 936	unit_free_rcu(this_cpu_ptr(ma->caches)->cache + idx, ptr);
 937}
 938
 939void notrace *bpf_mem_cache_alloc(struct bpf_mem_alloc *ma)
 940{
 941	void *ret;
 942
 943	ret = unit_alloc(this_cpu_ptr(ma->cache));
 944	return !ret ? NULL : ret + LLIST_NODE_SZ;
 945}
 946
 947void notrace bpf_mem_cache_free(struct bpf_mem_alloc *ma, void *ptr)
 948{
 949	if (!ptr)
 950		return;
 951
 952	unit_free(this_cpu_ptr(ma->cache), ptr);
 953}
 954
 955void notrace bpf_mem_cache_free_rcu(struct bpf_mem_alloc *ma, void *ptr)
 956{
 957	if (!ptr)
 958		return;
 959
 960	unit_free_rcu(this_cpu_ptr(ma->cache), ptr);
 961}
 962
 963/* Directly does a kfree() without putting 'ptr' back to the free_llist
 964 * for reuse and without waiting for a rcu_tasks_trace gp.
 965 * The caller must first go through the rcu_tasks_trace gp for 'ptr'
 966 * before calling bpf_mem_cache_raw_free().
 967 * It could be used when the rcu_tasks_trace callback does not have
 968 * a hold on the original bpf_mem_alloc object that allocated the
 969 * 'ptr'. This should only be used in the uncommon code path.
 970 * Otherwise, the bpf_mem_alloc's free_llist cannot be refilled
 971 * and may affect performance.
 972 */
 973void bpf_mem_cache_raw_free(void *ptr)
 974{
 975	if (!ptr)
 976		return;
 977
 978	kfree(ptr - LLIST_NODE_SZ);
 979}
 980
 981/* When flags == GFP_KERNEL, it signals that the caller will not cause
 982 * deadlock when using kmalloc. bpf_mem_cache_alloc_flags() will use
 983 * kmalloc if the free_llist is empty.
 984 */
 985void notrace *bpf_mem_cache_alloc_flags(struct bpf_mem_alloc *ma, gfp_t flags)
 986{
 987	struct bpf_mem_cache *c;
 988	void *ret;
 989
 990	c = this_cpu_ptr(ma->cache);
 991
 992	ret = unit_alloc(c);
 993	if (!ret && flags == GFP_KERNEL) {
 994		struct mem_cgroup *memcg, *old_memcg;
 995
 996		memcg = get_memcg(c);
 997		old_memcg = set_active_memcg(memcg);
 998		ret = __alloc(c, NUMA_NO_NODE, GFP_KERNEL | __GFP_NOWARN | __GFP_ACCOUNT);
 999		if (ret)
1000			*(struct bpf_mem_cache **)ret = c;
1001		set_active_memcg(old_memcg);
1002		mem_cgroup_put(memcg);
1003	}
1004
1005	return !ret ? NULL : ret + LLIST_NODE_SZ;
1006}
1007
1008int bpf_mem_alloc_check_size(bool percpu, size_t size)
1009{
1010	/* The size of percpu allocation doesn't have LLIST_NODE_SZ overhead */
1011	if ((percpu && size > BPF_MEM_ALLOC_SIZE_MAX) ||
1012	    (!percpu && size > BPF_MEM_ALLOC_SIZE_MAX - LLIST_NODE_SZ))
1013		return -E2BIG;
1014
1015	return 0;
1016}