// SPDX-License-Identifier: GPL-2.0-only
/* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */
#include <linux/mm.h>
#include <linux/llist.h>
#include <linux/bpf.h>
#include <linux/irq_work.h>
#include <linux/bpf_mem_alloc.h>
#include <linux/memcontrol.h>
#include <asm/local.h>

/* Any context (including NMI) BPF specific memory allocator.
 *
 * Tracing BPF programs can attach to kprobe and fentry. Hence they
 * run in unknown context where calling plain kmalloc() might not be safe.
 *
 * Front-end kmalloc() with per-cpu per-bucket cache of free elements.
 * Refill this cache asynchronously from irq_work.
 *
 * CPU_0 buckets
 * 16 32 64 96 128 196 256 512 1024 2048 4096
 * ...
 * CPU_N buckets
 * 16 32 64 96 128 196 256 512 1024 2048 4096
 *
 * The buckets are prefilled at the start.
 * BPF programs always run with migration disabled.
 * It's safe to allocate from cache of the current cpu with irqs disabled.
 * Free-ing is always done into bucket of the current cpu as well.
 * irq_work trims extra free elements from buckets with kfree
 * and refills them with kmalloc, so global kmalloc logic takes care
 * of freeing objects allocated by one cpu and freed on another.
 *
 * Every allocated objected is padded with extra 8 bytes that contains
 * struct llist_node.
 */
#define LLIST_NODE_SZ sizeof(struct llist_node)

#define BPF_MEM_ALLOC_SIZE_MAX 4096

/* similar to kmalloc, but sizeof == 8 bucket is gone */
static u8 size_index[24] __ro_after_init = {
        3,      /* 8 */
        3,      /* 16 */
        4,      /* 24 */
        4,      /* 32 */
        5,      /* 40 */
        5,      /* 48 */
        5,      /* 56 */
        5,      /* 64 */
        1,      /* 72 */
        1,      /* 80 */
        1,      /* 88 */
        1,      /* 96 */
        6,      /* 104 */
        6,      /* 112 */
        6,      /* 120 */
        6,      /* 128 */
        2,      /* 136 */
        2,      /* 144 */
        2,      /* 152 */
        2,      /* 160 */
        2,      /* 168 */
        2,      /* 176 */
        2,      /* 184 */
        2       /* 192 */
};

static int bpf_mem_cache_idx(size_t size)
{
        if (!size || size > BPF_MEM_ALLOC_SIZE_MAX)
                return -1;

        if (size <= 192)
                return size_index[(size - 1) / 8] - 1;

        return fls(size - 1) - 2;
}

#define NUM_CACHES 11

struct bpf_mem_cache {
        /* per-cpu list of free objects of size 'unit_size'.
         * All accesses are done with interrupts disabled and 'active' counter
         * protection with __llist_add() and __llist_del_first().
         */
        struct llist_head free_llist;
        local_t active;

        /* Operations on the free_list from unit_alloc/unit_free/bpf_mem_refill
         * are sequenced by per-cpu 'active' counter. But unit_free() cannot
         * fail. When 'active' is busy the unit_free() will add an object to
         * free_llist_extra.
         */
        struct llist_head free_llist_extra;

        struct irq_work refill_work;
        struct obj_cgroup *objcg;
        int unit_size;
        /* count of objects in free_llist */
        int free_cnt;
        int low_watermark, high_watermark, batch;
        int percpu_size;
        bool draining;
        struct bpf_mem_cache *tgt;
        void (*dtor)(void *obj, void *ctx);
        void *dtor_ctx;

        /* list of objects to be freed after RCU GP */
        struct llist_head free_by_rcu;
        struct llist_node *free_by_rcu_tail;
        struct llist_head waiting_for_gp;
        struct llist_node *waiting_for_gp_tail;
        struct rcu_head rcu;
        atomic_t call_rcu_in_progress;
        struct llist_head free_llist_extra_rcu;

        /* list of objects to be freed after RCU tasks trace GP */
        struct llist_head free_by_rcu_ttrace;
        struct llist_head waiting_for_gp_ttrace;
        struct rcu_head rcu_ttrace;
        atomic_t call_rcu_ttrace_in_progress;
};

struct bpf_mem_caches {
        struct bpf_mem_cache cache[NUM_CACHES];
};

static const u16 sizes[NUM_CACHES] = {96, 192, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096};

static struct llist_node notrace *__llist_del_first(struct llist_head *head)
{
        struct llist_node *entry, *next;

        entry = head->first;
        if (!entry)
                return NULL;
        next = entry->next;
        head->first = next;
        return entry;
}

static void *__alloc(struct bpf_mem_cache *c, int node, gfp_t flags)
{
        if (c->percpu_size) {
                void __percpu **obj = kmalloc_node(c->percpu_size, flags, node);
                void __percpu *pptr = __alloc_percpu_gfp(c->unit_size, 8, flags);

                if (!obj || !pptr) {
                        free_percpu(pptr);
                        kfree(obj);
                        return NULL;
                }
                obj[1] = pptr;
                return obj;
        }

        return kmalloc_node(c->unit_size, flags | __GFP_ZERO, node);
}

static struct mem_cgroup *get_memcg(const struct bpf_mem_cache *c)
{
#ifdef CONFIG_MEMCG
        if (c->objcg)
                return get_mem_cgroup_from_objcg(c->objcg);
        return root_mem_cgroup;
#else
        return NULL;
#endif
}

static void inc_active(struct bpf_mem_cache *c, unsigned long *flags)
{
        if (IS_ENABLED(CONFIG_PREEMPT_RT))
                /* In RT irq_work runs in per-cpu kthread, so disable
                 * interrupts to avoid preemption and interrupts and
                 * reduce the chance of bpf prog executing on this cpu
                 * when active counter is busy.
                 */
                local_irq_save(*flags);
        /* alloc_bulk runs from irq_work which will not preempt a bpf
         * program that does unit_alloc/unit_free since IRQs are
         * disabled there. There is no race to increment 'active'
         * counter. It protects free_llist from corruption in case NMI
         * bpf prog preempted this loop.
         */
        WARN_ON_ONCE(local_inc_return(&c->active) != 1);
}

static void dec_active(struct bpf_mem_cache *c, unsigned long *flags)
{
        local_dec(&c->active);
        if (IS_ENABLED(CONFIG_PREEMPT_RT))
                local_irq_restore(*flags);
}

static void add_obj_to_free_list(struct bpf_mem_cache *c, void *obj)
{
        unsigned long flags;

        inc_active(c, &flags);
        __llist_add(obj, &c->free_llist);
        c->free_cnt++;
        dec_active(c, &flags);
}

/* Mostly runs from irq_work except __init phase. */
static void alloc_bulk(struct bpf_mem_cache *c, int cnt, int node, bool atomic)
{
        struct mem_cgroup *memcg = NULL, *old_memcg;
        gfp_t gfp;
        void *obj;
        int i;

        gfp = __GFP_NOWARN | __GFP_ACCOUNT;
        gfp |= atomic ? GFP_NOWAIT : GFP_KERNEL;

        for (i = 0; i < cnt; i++) {
                /*
                 * For every 'c' llist_del_first(&c->free_by_rcu_ttrace); is
                 * done only by one CPU == current CPU. Other CPUs might
                 * llist_add() and llist_del_all() in parallel.
                 */
                obj = llist_del_first(&c->free_by_rcu_ttrace);
                if (!obj)
                        break;
                add_obj_to_free_list(c, obj);
        }
        if (i >= cnt)
                return;

        for (; i < cnt; i++) {
                obj = llist_del_first(&c->waiting_for_gp_ttrace);
                if (!obj)
                        break;
                add_obj_to_free_list(c, obj);
        }
        if (i >= cnt)
                return;

        memcg = get_memcg(c);
        old_memcg = set_active_memcg(memcg);
        for (; i < cnt; i++) {
                /* Allocate, but don't deplete atomic reserves that typical
                 * GFP_ATOMIC would do. irq_work runs on this cpu and kmalloc
                 * will allocate from the current numa node which is what we
                 * want here.
                 */
                obj = __alloc(c, node, gfp);
                if (!obj)
                        break;
                add_obj_to_free_list(c, obj);
        }
        set_active_memcg(old_memcg);
        mem_cgroup_put(memcg);
}

static void free_one(void *obj, bool percpu)
{
        if (percpu)
                free_percpu(((void __percpu **)obj)[1]);

        kfree(obj);
}

static int free_all(struct bpf_mem_cache *c, struct llist_node *llnode, bool percpu)
{
        struct llist_node *pos, *t;
        int cnt = 0;

        llist_for_each_safe(pos, t, llnode) {
                if (c->dtor)
                        c->dtor((void *)pos + LLIST_NODE_SZ, c->dtor_ctx);
                free_one(pos, percpu);
                cnt++;
        }
        return cnt;
}

static void __free_rcu(struct rcu_head *head)
{
        struct bpf_mem_cache *c = container_of(head, struct bpf_mem_cache, rcu_ttrace);

        free_all(c, llist_del_all(&c->waiting_for_gp_ttrace), !!c->percpu_size);
        atomic_set(&c->call_rcu_ttrace_in_progress, 0);
}

static void __free_rcu_tasks_trace(struct rcu_head *head)
{
        /* If RCU Tasks Trace grace period implies RCU grace period,
         * there is no need to invoke call_rcu().
         */
        if (rcu_trace_implies_rcu_gp())
                __free_rcu(head);
        else
                call_rcu(head, __free_rcu);
}

static void enque_to_free(struct bpf_mem_cache *c, void *obj)
{
        struct llist_node *llnode = obj;

        /* bpf_mem_cache is a per-cpu object. Freeing happens in irq_work.
         * Nothing races to add to free_by_rcu_ttrace list.
         */
        llist_add(llnode, &c->free_by_rcu_ttrace);
}

static void do_call_rcu_ttrace(struct bpf_mem_cache *c)
{
        struct llist_node *llnode, *t;

        if (atomic_xchg(&c->call_rcu_ttrace_in_progress, 1)) {
                if (unlikely(READ_ONCE(c->draining))) {
                        llnode = llist_del_all(&c->free_by_rcu_ttrace);
                        free_all(c, llnode, !!c->percpu_size);
                }
                return;
        }

        WARN_ON_ONCE(!llist_empty(&c->waiting_for_gp_ttrace));
        llist_for_each_safe(llnode, t, llist_del_all(&c->free_by_rcu_ttrace))
                llist_add(llnode, &c->waiting_for_gp_ttrace);

        if (unlikely(READ_ONCE(c->draining))) {
                __free_rcu(&c->rcu_ttrace);
                return;
        }

        /* Use call_rcu_tasks_trace() to wait for sleepable progs to finish.
         * If RCU Tasks Trace grace period implies RCU grace period, free
         * these elements directly, else use call_rcu() to wait for normal
         * progs to finish and finally do free_one() on each element.
         */
        call_rcu_tasks_trace(&c->rcu_ttrace, __free_rcu_tasks_trace);
}

static void free_bulk(struct bpf_mem_cache *c)
{
        struct bpf_mem_cache *tgt = c->tgt;
        struct llist_node *llnode, *t;
        unsigned long flags;
        int cnt;

        WARN_ON_ONCE(tgt->unit_size != c->unit_size);
        WARN_ON_ONCE(tgt->percpu_size != c->percpu_size);

        do {
                inc_active(c, &flags);
                llnode = __llist_del_first(&c->free_llist);
                if (llnode)
                        cnt = --c->free_cnt;
                else
                        cnt = 0;
                dec_active(c, &flags);
                if (llnode)
                        enque_to_free(tgt, llnode);
        } while (cnt > (c->high_watermark + c->low_watermark) / 2);

        /* and drain free_llist_extra */
        llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist_extra))
                enque_to_free(tgt, llnode);
        do_call_rcu_ttrace(tgt);
}

static void __free_by_rcu(struct rcu_head *head)
{
        struct bpf_mem_cache *c = container_of(head, struct bpf_mem_cache, rcu);
        struct bpf_mem_cache *tgt = c->tgt;
        struct llist_node *llnode;

        WARN_ON_ONCE(tgt->unit_size != c->unit_size);
        WARN_ON_ONCE(tgt->percpu_size != c->percpu_size);

        llnode = llist_del_all(&c->waiting_for_gp);
        if (!llnode)
                goto out;

        llist_add_batch(llnode, c->waiting_for_gp_tail, &tgt->free_by_rcu_ttrace);

        /* Objects went through regular RCU GP. Send them to RCU tasks trace */
        do_call_rcu_ttrace(tgt);
out:
        atomic_set(&c->call_rcu_in_progress, 0);
}

static void check_free_by_rcu(struct bpf_mem_cache *c)
{
        struct llist_node *llnode, *t;
        unsigned long flags;

        /* drain free_llist_extra_rcu */
        if (unlikely(!llist_empty(&c->free_llist_extra_rcu))) {
                inc_active(c, &flags);
                llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist_extra_rcu))
                        if (__llist_add(llnode, &c->free_by_rcu))
                                c->free_by_rcu_tail = llnode;
                dec_active(c, &flags);
        }

        if (llist_empty(&c->free_by_rcu))
                return;

        if (atomic_xchg(&c->call_rcu_in_progress, 1)) {
                /*
                 * Instead of kmalloc-ing new rcu_head and triggering 10k
                 * call_rcu() to hit rcutree.qhimark and force RCU to notice
                 * the overload just ask RCU to hurry up. There could be many
                 * objects in free_by_rcu list.
                 * This hint reduces memory consumption for an artificial
                 * benchmark from 2 Gbyte to 150 Mbyte.
                 */
                rcu_request_urgent_qs_task(current);
                return;
        }

        WARN_ON_ONCE(!llist_empty(&c->waiting_for_gp));

        inc_active(c, &flags);
        WRITE_ONCE(c->waiting_for_gp.first, __llist_del_all(&c->free_by_rcu));
        c->waiting_for_gp_tail = c->free_by_rcu_tail;
        dec_active(c, &flags);

        if (unlikely(READ_ONCE(c->draining))) {
                free_all(c, llist_del_all(&c->waiting_for_gp), !!c->percpu_size);
                atomic_set(&c->call_rcu_in_progress, 0);
        } else {
                call_rcu_hurry(&c->rcu, __free_by_rcu);
        }
}

static void bpf_mem_refill(struct irq_work *work)
{
        struct bpf_mem_cache *c = container_of(work, struct bpf_mem_cache, refill_work);
        int cnt;

        /* Racy access to free_cnt. It doesn't need to be 100% accurate */
        cnt = c->free_cnt;
        if (cnt < c->low_watermark)
                /* irq_work runs on this cpu and kmalloc will allocate
                 * from the current numa node which is what we want here.
                 */
                alloc_bulk(c, c->batch, NUMA_NO_NODE, true);
        else if (cnt > c->high_watermark)
                free_bulk(c);

        check_free_by_rcu(c);
}

static void notrace irq_work_raise(struct bpf_mem_cache *c)
{
        irq_work_queue(&c->refill_work);
}

/* For typical bpf map case that uses bpf_mem_cache_alloc and single bucket
 * the freelist cache will be elem_size * 64 (or less) on each cpu.
 *
 * For bpf programs that don't have statically known allocation sizes and
 * assuming (low_mark + high_mark) / 2 as an average number of elements per
 * bucket and all buckets are used the total amount of memory in freelists
 * on each cpu will be:
 * 64*16 + 64*32 + 64*64 + 64*96 + 64*128 + 64*196 + 64*256 + 32*512 + 16*1024 + 8*2048 + 4*4096
 * == ~ 116 Kbyte using below heuristic.
 * Initialized, but unused bpf allocator (not bpf map specific one) will
 * consume ~ 11 Kbyte per cpu.
 * Typical case will be between 11K and 116K closer to 11K.
 * bpf progs can and should share bpf_mem_cache when possible.
 *
 * Percpu allocation is typically rare. To avoid potential unnecessary large
 * memory consumption, set low_mark = 1 and high_mark = 3, resulting in c->batch = 1.
 */
static void init_refill_work(struct bpf_mem_cache *c)
{
        init_irq_work(&c->refill_work, bpf_mem_refill);
        if (c->percpu_size) {
                c->low_watermark = 1;
                c->high_watermark = 3;
        } else if (c->unit_size <= 256) {
                c->low_watermark = 32;
                c->high_watermark = 96;
        } else {
                /* When page_size == 4k, order-0 cache will have low_mark == 2
                 * and high_mark == 6 with batch alloc of 3 individual pages at
                 * a time.
                 * 8k allocs and above low == 1, high == 3, batch == 1.
                 */
                c->low_watermark = max(32 * 256 / c->unit_size, 1);
                c->high_watermark = max(96 * 256 / c->unit_size, 3);
        }
        c->batch = max((c->high_watermark - c->low_watermark) / 4 * 3, 1);
}

static void prefill_mem_cache(struct bpf_mem_cache *c, int cpu)
{
        int cnt = 1;

        /* To avoid consuming memory, for non-percpu allocation, assume that
         * 1st run of bpf prog won't be doing more than 4 map_update_elem from
         * irq disabled region if unit size is less than or equal to 256.
         * For all other cases, let us just do one allocation.
         */
        if (!c->percpu_size && c->unit_size <= 256)
                cnt = 4;
        alloc_bulk(c, cnt, cpu_to_node(cpu), false);
}

/* When size != 0 bpf_mem_cache for each cpu.
 * This is typical bpf hash map use case when all elements have equal size.
 *
 * When size == 0 allocate 11 bpf_mem_cache-s for each cpu, then rely on
 * kmalloc/kfree. Max allocation size is 4096 in this case.
 * This is bpf_dynptr and bpf_kptr use case.
 */
int bpf_mem_alloc_init(struct bpf_mem_alloc *ma, int size, bool percpu)
{
        struct bpf_mem_caches *cc; struct bpf_mem_caches __percpu *pcc;
        struct bpf_mem_cache *c; struct bpf_mem_cache __percpu *pc;
        struct obj_cgroup *objcg = NULL;
        int cpu, i, unit_size, percpu_size = 0;

        if (percpu && size == 0)
                return -EINVAL;

        /* room for llist_node and per-cpu pointer */
        if (percpu)
                percpu_size = LLIST_NODE_SZ + sizeof(void *);
        ma->percpu = percpu;

        if (size) {
                pc = __alloc_percpu_gfp(sizeof(*pc), 8, GFP_KERNEL);
                if (!pc)
                        return -ENOMEM;

                if (!percpu)
                        size += LLIST_NODE_SZ; /* room for llist_node */
                unit_size = size;

#ifdef CONFIG_MEMCG
                if (memcg_bpf_enabled())
                        objcg = get_obj_cgroup_from_current();
#endif
                ma->objcg = objcg;

                for_each_possible_cpu(cpu) {
                        c = per_cpu_ptr(pc, cpu);
                        c->unit_size = unit_size;
                        c->objcg = objcg;
                        c->percpu_size = percpu_size;
                        c->tgt = c;
                        init_refill_work(c);
                        prefill_mem_cache(c, cpu);
                }
                ma->cache = pc;
                return 0;
        }

        pcc = __alloc_percpu_gfp(sizeof(*cc), 8, GFP_KERNEL);
        if (!pcc)
                return -ENOMEM;
#ifdef CONFIG_MEMCG
        objcg = get_obj_cgroup_from_current();
#endif
        ma->objcg = objcg;
        for_each_possible_cpu(cpu) {
                cc = per_cpu_ptr(pcc, cpu);
                for (i = 0; i < NUM_CACHES; i++) {
                        c = &cc->cache[i];
                        c->unit_size = sizes[i];
                        c->objcg = objcg;
                        c->percpu_size = percpu_size;
                        c->tgt = c;

                        init_refill_work(c);
                        prefill_mem_cache(c, cpu);
                }
        }

        ma->caches = pcc;
        return 0;
}

int bpf_mem_alloc_percpu_init(struct bpf_mem_alloc *ma, struct obj_cgroup *objcg)
{
        struct bpf_mem_caches __percpu *pcc;

        pcc = __alloc_percpu_gfp(sizeof(struct bpf_mem_caches), 8, GFP_KERNEL);
        if (!pcc)
                return -ENOMEM;

        ma->caches = pcc;
        ma->objcg = objcg;
        ma->percpu = true;
        return 0;
}

int bpf_mem_alloc_percpu_unit_init(struct bpf_mem_alloc *ma, int size)
{
        struct bpf_mem_caches *cc; struct bpf_mem_caches __percpu *pcc;
        int cpu, i, unit_size, percpu_size;
        struct obj_cgroup *objcg;
        struct bpf_mem_cache *c;

        i = bpf_mem_cache_idx(size);
        if (i < 0)
                return -EINVAL;

        /* room for llist_node and per-cpu pointer */
        percpu_size = LLIST_NODE_SZ + sizeof(void *);

        unit_size = sizes[i];
        objcg = ma->objcg;
        pcc = ma->caches;

        for_each_possible_cpu(cpu) {
                cc = per_cpu_ptr(pcc, cpu);
                c = &cc->cache[i];
                if (c->unit_size)
                        break;

                c->unit_size = unit_size;
                c->objcg = objcg;
                c->percpu_size = percpu_size;
                c->tgt = c;

                init_refill_work(c);
                prefill_mem_cache(c, cpu);
        }

        return 0;
}

static void drain_mem_cache(struct bpf_mem_cache *c)
{
        bool percpu = !!c->percpu_size;

        /* No progs are using this bpf_mem_cache, but htab_map_free() called
         * bpf_mem_cache_free() for all remaining elements and they can be in
         * free_by_rcu_ttrace or in waiting_for_gp_ttrace lists, so drain those lists now.
         *
         * Except for waiting_for_gp_ttrace list, there are no concurrent operations
         * on these lists, so it is safe to use __llist_del_all().
         */
        free_all(c, llist_del_all(&c->free_by_rcu_ttrace), percpu);
        free_all(c, llist_del_all(&c->waiting_for_gp_ttrace), percpu);
        free_all(c, __llist_del_all(&c->free_llist), percpu);
        free_all(c, __llist_del_all(&c->free_llist_extra), percpu);
        free_all(c, __llist_del_all(&c->free_by_rcu), percpu);
        free_all(c, __llist_del_all(&c->free_llist_extra_rcu), percpu);
        free_all(c, llist_del_all(&c->waiting_for_gp), percpu);
}

static void check_mem_cache(struct bpf_mem_cache *c)
{
        WARN_ON_ONCE(!llist_empty(&c->free_by_rcu_ttrace));
        WARN_ON_ONCE(!llist_empty(&c->waiting_for_gp_ttrace));
        WARN_ON_ONCE(!llist_empty(&c->free_llist));
        WARN_ON_ONCE(!llist_empty(&c->free_llist_extra));
        WARN_ON_ONCE(!llist_empty(&c->free_by_rcu));
        WARN_ON_ONCE(!llist_empty(&c->free_llist_extra_rcu));
        WARN_ON_ONCE(!llist_empty(&c->waiting_for_gp));
}

static void check_leaked_objs(struct bpf_mem_alloc *ma)
{
        struct bpf_mem_caches *cc;
        struct bpf_mem_cache *c;
        int cpu, i;

        if (ma->cache) {
                for_each_possible_cpu(cpu) {
                        c = per_cpu_ptr(ma->cache, cpu);
                        check_mem_cache(c);
                }
        }
        if (ma->caches) {
                for_each_possible_cpu(cpu) {
                        cc = per_cpu_ptr(ma->caches, cpu);
                        for (i = 0; i < NUM_CACHES; i++) {
                                c = &cc->cache[i];
                                check_mem_cache(c);
                        }
                }
        }
}

static void free_mem_alloc_no_barrier(struct bpf_mem_alloc *ma)
{
        /* We can free dtor ctx only once all callbacks are done using it. */
        if (ma->dtor_ctx_free)
                ma->dtor_ctx_free(ma->dtor_ctx);
        check_leaked_objs(ma);
        free_percpu(ma->cache);
        free_percpu(ma->caches);
        ma->cache = NULL;
        ma->caches = NULL;
}

static void free_mem_alloc(struct bpf_mem_alloc *ma)
{
        /* waiting_for_gp[_ttrace] lists were drained, but RCU callbacks
         * might still execute. Wait for them.
         *
         * rcu_barrier_tasks_trace() doesn't imply synchronize_rcu_tasks_trace(),
         * but rcu_barrier_tasks_trace() and rcu_barrier() below are only used
         * to wait for the pending __free_rcu_tasks_trace() and __free_rcu(),
         * so if call_rcu(head, __free_rcu) is skipped due to
         * rcu_trace_implies_rcu_gp(), it will be OK to skip rcu_barrier() by
         * using rcu_trace_implies_rcu_gp() as well.
         */
        rcu_barrier(); /* wait for __free_by_rcu */
        rcu_barrier_tasks_trace(); /* wait for __free_rcu */
        if (!rcu_trace_implies_rcu_gp())
                rcu_barrier();
        free_mem_alloc_no_barrier(ma);
}

static void free_mem_alloc_deferred(struct work_struct *work)
{
        struct bpf_mem_alloc *ma = container_of(work, struct bpf_mem_alloc, work);

        free_mem_alloc(ma);
        kfree(ma);
}

static void destroy_mem_alloc(struct bpf_mem_alloc *ma, int rcu_in_progress)
{
        struct bpf_mem_alloc *copy;

        if (!rcu_in_progress) {
                /* Fast path. No callbacks are pending, hence no need to do
                 * rcu_barrier-s.
                 */
                free_mem_alloc_no_barrier(ma);
                return;
        }

        copy = kmemdup(ma, sizeof(*ma), GFP_KERNEL);
        if (!copy) {
                /* Slow path with inline barrier-s */
                free_mem_alloc(ma);
                return;
        }

        /* Defer barriers into worker to let the rest of map memory to be freed */
        memset(ma, 0, sizeof(*ma));
        INIT_WORK(&copy->work, free_mem_alloc_deferred);
        queue_work(system_dfl_wq, &copy->work);
}

void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma)
{
        struct bpf_mem_caches *cc;
        struct bpf_mem_cache *c;
        int cpu, i, rcu_in_progress;

        if (ma->cache) {
                rcu_in_progress = 0;
                for_each_possible_cpu(cpu) {
                        c = per_cpu_ptr(ma->cache, cpu);
                        WRITE_ONCE(c->draining, true);
                        irq_work_sync(&c->refill_work);
                        drain_mem_cache(c);
                        rcu_in_progress += atomic_read(&c->call_rcu_ttrace_in_progress);
                        rcu_in_progress += atomic_read(&c->call_rcu_in_progress);
                }
                obj_cgroup_put(ma->objcg);
                destroy_mem_alloc(ma, rcu_in_progress);
        }
        if (ma->caches) {
                rcu_in_progress = 0;
                for_each_possible_cpu(cpu) {
                        cc = per_cpu_ptr(ma->caches, cpu);
                        for (i = 0; i < NUM_CACHES; i++) {
                                c = &cc->cache[i];
                                WRITE_ONCE(c->draining, true);
                                irq_work_sync(&c->refill_work);
                                drain_mem_cache(c);
                                rcu_in_progress += atomic_read(&c->call_rcu_ttrace_in_progress);
                                rcu_in_progress += atomic_read(&c->call_rcu_in_progress);
                        }
                }
                obj_cgroup_put(ma->objcg);
                destroy_mem_alloc(ma, rcu_in_progress);
        }
}

/* notrace is necessary here and in other functions to make sure
 * bpf programs cannot attach to them and cause llist corruptions.
 */
static void notrace *unit_alloc(struct bpf_mem_cache *c)
{
        struct llist_node *llnode = NULL;
        unsigned long flags;
        int cnt = 0;

        /* Disable irqs to prevent the following race for majority of prog types:
         * prog_A
         *   bpf_mem_alloc
         *      preemption or irq -> prog_B
         *        bpf_mem_alloc
         *
         * but prog_B could be a perf_event NMI prog.
         * Use per-cpu 'active' counter to order free_list access between
         * unit_alloc/unit_free/bpf_mem_refill.
         */
        local_irq_save(flags);
        if (local_inc_return(&c->active) == 1) {
                llnode = __llist_del_first(&c->free_llist);
                if (llnode) {
                        cnt = --c->free_cnt;
                        *(struct bpf_mem_cache **)llnode = c;
                }
        }
        local_dec(&c->active);

        WARN_ON(cnt < 0);

        if (cnt < c->low_watermark)
                irq_work_raise(c);
        /* Enable IRQ after the enqueue of irq work completes, so irq work
         * will run after IRQ is enabled and free_llist may be refilled by
         * irq work before other task preempts current task.
         */
        local_irq_restore(flags);

        return llnode;
}

/* Though 'ptr' object could have been allocated on a different cpu
 * add it to the free_llist of the current cpu.
 * Let kfree() logic deal with it when it's later called from irq_work.
 */
static void notrace unit_free(struct bpf_mem_cache *c, void *ptr)
{
        struct llist_node *llnode = ptr - LLIST_NODE_SZ;
        unsigned long flags;
        int cnt = 0;

        BUILD_BUG_ON(LLIST_NODE_SZ > 8);

        /*
         * Remember bpf_mem_cache that allocated this object.
         * The hint is not accurate.
         */
        c->tgt = *(struct bpf_mem_cache **)llnode;

        local_irq_save(flags);
        if (local_inc_return(&c->active) == 1) {
                __llist_add(llnode, &c->free_llist);
                cnt = ++c->free_cnt;
        } else {
                /* unit_free() cannot fail. Therefore add an object to atomic
                 * llist. free_bulk() will drain it. Though free_llist_extra is
                 * a per-cpu list we have to use atomic llist_add here, since
                 * it also can be interrupted by bpf nmi prog that does another
                 * unit_free() into the same free_llist_extra.
                 */
                llist_add(llnode, &c->free_llist_extra);
        }
        local_dec(&c->active);

        if (cnt > c->high_watermark)
                /* free few objects from current cpu into global kmalloc pool */
                irq_work_raise(c);
        /* Enable IRQ after irq_work_raise() completes, otherwise when current
         * task is preempted by task which does unit_alloc(), unit_alloc() may
         * return NULL unexpectedly because irq work is already pending but can
         * not been triggered and free_llist can not be refilled timely.
         */
        local_irq_restore(flags);
}

static void notrace unit_free_rcu(struct bpf_mem_cache *c, void *ptr)
{
        struct llist_node *llnode = ptr - LLIST_NODE_SZ;
        unsigned long flags;

        c->tgt = *(struct bpf_mem_cache **)llnode;

        local_irq_save(flags);
        if (local_inc_return(&c->active) == 1) {
                if (__llist_add(llnode, &c->free_by_rcu))
                        c->free_by_rcu_tail = llnode;
        } else {
                llist_add(llnode, &c->free_llist_extra_rcu);
        }
        local_dec(&c->active);

        if (!atomic_read(&c->call_rcu_in_progress))
                irq_work_raise(c);
        local_irq_restore(flags);
}

/* Called from BPF program or from sys_bpf syscall.
 * In both cases migration is disabled.
 */
void notrace *bpf_mem_alloc(struct bpf_mem_alloc *ma, size_t size)
{
        int idx;
        void *ret;

        if (!size)
                return NULL;

        if (!ma->percpu)
                size += LLIST_NODE_SZ;
        idx = bpf_mem_cache_idx(size);
        if (idx < 0)
                return NULL;

        ret = unit_alloc(this_cpu_ptr(ma->caches)->cache + idx);
        return !ret ? NULL : ret + LLIST_NODE_SZ;
}

void notrace bpf_mem_free(struct bpf_mem_alloc *ma, void *ptr)
{
        struct bpf_mem_cache *c;
        int idx;

        if (!ptr)
                return;

        c = *(void **)(ptr - LLIST_NODE_SZ);
        idx = bpf_mem_cache_idx(c->unit_size);
        if (WARN_ON_ONCE(idx < 0))
                return;

        unit_free(this_cpu_ptr(ma->caches)->cache + idx, ptr);
}

void notrace bpf_mem_free_rcu(struct bpf_mem_alloc *ma, void *ptr)
{
        struct bpf_mem_cache *c;
        int idx;

        if (!ptr)
                return;

        c = *(void **)(ptr - LLIST_NODE_SZ);
        idx = bpf_mem_cache_idx(c->unit_size);
        if (WARN_ON_ONCE(idx < 0))
                return;

        unit_free_rcu(this_cpu_ptr(ma->caches)->cache + idx, ptr);
}

void notrace *bpf_mem_cache_alloc(struct bpf_mem_alloc *ma)
{
        void *ret;

        ret = unit_alloc(this_cpu_ptr(ma->cache));
        return !ret ? NULL : ret + LLIST_NODE_SZ;
}

void notrace bpf_mem_cache_free(struct bpf_mem_alloc *ma, void *ptr)
{
        if (!ptr)
                return;

        unit_free(this_cpu_ptr(ma->cache), ptr);
}

void notrace bpf_mem_cache_free_rcu(struct bpf_mem_alloc *ma, void *ptr)
{
        if (!ptr)
                return;

        unit_free_rcu(this_cpu_ptr(ma->cache), ptr);
}

/* Directly does a kfree() without putting 'ptr' back to the free_llist
 * for reuse and without waiting for a rcu_tasks_trace gp.
 * The caller must first go through the rcu_tasks_trace gp for 'ptr'
 * before calling bpf_mem_cache_raw_free().
 * It could be used when the rcu_tasks_trace callback does not have
 * a hold on the original bpf_mem_alloc object that allocated the
 * 'ptr'. This should only be used in the uncommon code path.
 * Otherwise, the bpf_mem_alloc's free_llist cannot be refilled
 * and may affect performance.
 */
void bpf_mem_cache_raw_free(void *ptr)
{
        if (!ptr)
                return;

        kfree(ptr - LLIST_NODE_SZ);
}

/* When flags == GFP_KERNEL, it signals that the caller will not cause
 * deadlock when using kmalloc. bpf_mem_cache_alloc_flags() will use
 * kmalloc if the free_llist is empty.
 */
void notrace *bpf_mem_cache_alloc_flags(struct bpf_mem_alloc *ma, gfp_t flags)
{
        struct bpf_mem_cache *c;
        void *ret;

        c = this_cpu_ptr(ma->cache);

        ret = unit_alloc(c);
        if (!ret && flags == GFP_KERNEL) {
                struct mem_cgroup *memcg, *old_memcg;

                memcg = get_memcg(c);
                old_memcg = set_active_memcg(memcg);
                ret = __alloc(c, NUMA_NO_NODE, GFP_KERNEL | __GFP_NOWARN | __GFP_ACCOUNT);
                if (ret)
                        *(struct bpf_mem_cache **)ret = c;
                set_active_memcg(old_memcg);
                mem_cgroup_put(memcg);
        }

        return !ret ? NULL : ret + LLIST_NODE_SZ;
}

int bpf_mem_alloc_check_size(bool percpu, size_t size)
{
        /* The size of percpu allocation doesn't have LLIST_NODE_SZ overhead */
        if ((percpu && size > BPF_MEM_ALLOC_SIZE_MAX) ||
            (!percpu && size > BPF_MEM_ALLOC_SIZE_MAX - LLIST_NODE_SZ))
                return -E2BIG;

        return 0;
}

void bpf_mem_alloc_set_dtor(struct bpf_mem_alloc *ma, void (*dtor)(void *obj, void *ctx),
                            void (*dtor_ctx_free)(void *ctx), void *ctx)
{
        struct bpf_mem_caches *cc;
        struct bpf_mem_cache *c;
        int cpu, i;

        ma->dtor_ctx_free = dtor_ctx_free;
        ma->dtor_ctx = ctx;

        if (ma->cache) {
                for_each_possible_cpu(cpu) {
                        c = per_cpu_ptr(ma->cache, cpu);
                        c->dtor = dtor;
                        c->dtor_ctx = ctx;
                }
        }
        if (ma->caches) {
                for_each_possible_cpu(cpu) {
                        cc = per_cpu_ptr(ma->caches, cpu);
                        for (i = 0; i < NUM_CACHES; i++) {
                                c = &cc->cache[i];
                                c->dtor = dtor;
                                c->dtor_ctx = ctx;
                        }
                }
        }
}