// SPDX-License-Identifier: GPL-2.0-only
/* Copyright (c) 2016 Facebook
 */
#include <linux/bpf.h>
#include <linux/jhash.h>
#include <linux/filter.h>
#include <linux/kernel.h>
#include <linux/stacktrace.h>
#include <linux/perf_event.h>
#include <linux/btf_ids.h>
#include <linux/buildid.h>
#include "percpu_freelist.h"
#include "mmap_unlock_work.h"

#define STACK_CREATE_FLAG_MASK                                  \
        (BPF_F_NUMA_NODE | BPF_F_RDONLY | BPF_F_WRONLY |        \
         BPF_F_STACK_BUILD_ID)

struct stack_map_bucket {
        struct pcpu_freelist_node fnode;
        u32 hash;
        u32 nr;
        u64 data[];
};

struct bpf_stack_map {
        struct bpf_map map;
        void *elems;
        struct pcpu_freelist freelist;
        u32 n_buckets;
        struct stack_map_bucket *buckets[] __counted_by(n_buckets);
};

static inline bool stack_map_use_build_id(struct bpf_map *map)
{
        return (map->map_flags & BPF_F_STACK_BUILD_ID);
}

static inline int stack_map_data_size(struct bpf_map *map)
{
        return stack_map_use_build_id(map) ?
                sizeof(struct bpf_stack_build_id) : sizeof(u64);
}

/**
 * stack_map_calculate_max_depth - Calculate maximum allowed stack trace depth
 * @size:  Size of the buffer/map value in bytes
 * @elem_size:  Size of each stack trace element
 * @flags:  BPF stack trace flags (BPF_F_USER_STACK, BPF_F_USER_BUILD_ID, ...)
 *
 * Return: Maximum number of stack trace entries that can be safely stored
 */
static u32 stack_map_calculate_max_depth(u32 size, u32 elem_size, u64 flags)
{
        u32 skip = flags & BPF_F_SKIP_FIELD_MASK;
        u32 max_depth;
        u32 curr_sysctl_max_stack = READ_ONCE(sysctl_perf_event_max_stack);

        max_depth = size / elem_size;
        max_depth += skip;
        if (max_depth > curr_sysctl_max_stack)
                return curr_sysctl_max_stack;

        return max_depth;
}

static int prealloc_elems_and_freelist(struct bpf_stack_map *smap)
{
        u64 elem_size = sizeof(struct stack_map_bucket) +
                        (u64)smap->map.value_size;
        int err;

        smap->elems = bpf_map_area_alloc(elem_size * smap->map.max_entries,
                                         smap->map.numa_node);
        if (!smap->elems)
                return -ENOMEM;

        err = pcpu_freelist_init(&smap->freelist);
        if (err)
                goto free_elems;

        pcpu_freelist_populate(&smap->freelist, smap->elems, elem_size,
                               smap->map.max_entries);
        return 0;

free_elems:
        bpf_map_area_free(smap->elems);
        return err;
}

/* Called from syscall */
static struct bpf_map *stack_map_alloc(union bpf_attr *attr)
{
        u32 value_size = attr->value_size;
        struct bpf_stack_map *smap;
        u64 cost, n_buckets;
        int err;

        if (attr->map_flags & ~STACK_CREATE_FLAG_MASK)
                return ERR_PTR(-EINVAL);

        /* check sanity of attributes */
        if (attr->max_entries == 0 || attr->key_size != 4 ||
            value_size < 8 || value_size % 8)
                return ERR_PTR(-EINVAL);

        BUILD_BUG_ON(sizeof(struct bpf_stack_build_id) % sizeof(u64));
        if (attr->map_flags & BPF_F_STACK_BUILD_ID) {
                if (value_size % sizeof(struct bpf_stack_build_id) ||
                    value_size / sizeof(struct bpf_stack_build_id)
                    > sysctl_perf_event_max_stack)
                        return ERR_PTR(-EINVAL);
        } else if (value_size / 8 > sysctl_perf_event_max_stack)
                return ERR_PTR(-EINVAL);

        /* hash table size must be power of 2; roundup_pow_of_two() can overflow
         * into UB on 32-bit arches, so check that first
         */
        if (attr->max_entries > 1UL << 31)
                return ERR_PTR(-E2BIG);

        n_buckets = roundup_pow_of_two(attr->max_entries);

        cost = n_buckets * sizeof(struct stack_map_bucket *) + sizeof(*smap);
        smap = bpf_map_area_alloc(cost, bpf_map_attr_numa_node(attr));
        if (!smap)
                return ERR_PTR(-ENOMEM);

        bpf_map_init_from_attr(&smap->map, attr);
        smap->n_buckets = n_buckets;

        err = get_callchain_buffers(sysctl_perf_event_max_stack);
        if (err)
                goto free_smap;

        err = prealloc_elems_and_freelist(smap);
        if (err)
                goto put_buffers;

        return &smap->map;

put_buffers:
        put_callchain_buffers();
free_smap:
        bpf_map_area_free(smap);
        return ERR_PTR(err);
}

static int fetch_build_id(struct vm_area_struct *vma, unsigned char *build_id, bool may_fault)
{
        return may_fault ? build_id_parse(vma, build_id, NULL)
                         : build_id_parse_nofault(vma, build_id, NULL);
}

/*
 * Expects all id_offs[i].ip values to be set to correct initial IPs.
 * They will be subsequently:
 *   - either adjusted in place to a file offset, if build ID fetching
 *     succeeds; in this case id_offs[i].build_id is set to correct build ID,
 *     and id_offs[i].status is set to BPF_STACK_BUILD_ID_VALID;
 *   - or IP will be kept intact, if build ID fetching failed; in this case
 *     id_offs[i].build_id is zeroed out and id_offs[i].status is set to
 *     BPF_STACK_BUILD_ID_IP.
 */
static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
                                          u32 trace_nr, bool user, bool may_fault)
{
        int i;
        struct mmap_unlock_irq_work *work = NULL;
        bool irq_work_busy = bpf_mmap_unlock_get_irq_work(&work);
        struct vm_area_struct *vma, *prev_vma = NULL;
        const char *prev_build_id;

        /* If the irq_work is in use, fall back to report ips. Same
         * fallback is used for kernel stack (!user) on a stackmap with
         * build_id.
         */
        if (!user || !current || !current->mm || irq_work_busy ||
            !mmap_read_trylock(current->mm)) {
                /* cannot access current->mm, fall back to ips */
                for (i = 0; i < trace_nr; i++) {
                        id_offs[i].status = BPF_STACK_BUILD_ID_IP;
                        memset(id_offs[i].build_id, 0, BUILD_ID_SIZE_MAX);
                }
                return;
        }

        for (i = 0; i < trace_nr; i++) {
                u64 ip = READ_ONCE(id_offs[i].ip);

                if (range_in_vma(prev_vma, ip, ip)) {
                        vma = prev_vma;
                        memcpy(id_offs[i].build_id, prev_build_id, BUILD_ID_SIZE_MAX);
                        goto build_id_valid;
                }
                vma = find_vma(current->mm, ip);
                if (!vma || fetch_build_id(vma, id_offs[i].build_id, may_fault)) {
                        /* per entry fall back to ips */
                        id_offs[i].status = BPF_STACK_BUILD_ID_IP;
                        memset(id_offs[i].build_id, 0, BUILD_ID_SIZE_MAX);
                        continue;
                }
build_id_valid:
                id_offs[i].offset = (vma->vm_pgoff << PAGE_SHIFT) + ip - vma->vm_start;
                id_offs[i].status = BPF_STACK_BUILD_ID_VALID;
                prev_vma = vma;
                prev_build_id = id_offs[i].build_id;
        }
        bpf_mmap_unlock_mm(work, current->mm);
}

static struct perf_callchain_entry *
get_callchain_entry_for_task(struct task_struct *task, u32 max_depth)
{
#ifdef CONFIG_STACKTRACE
        struct perf_callchain_entry *entry;
        int rctx;

        entry = get_callchain_entry(&rctx);

        if (!entry)
                return NULL;

        entry->nr = stack_trace_save_tsk(task, (unsigned long *)entry->ip,
                                         max_depth, 0);

        /* stack_trace_save_tsk() works on unsigned long array, while
         * perf_callchain_entry uses u64 array. For 32-bit systems, it is
         * necessary to fix this mismatch.
         */
        if (__BITS_PER_LONG != 64) {
                unsigned long *from = (unsigned long *) entry->ip;
                u64 *to = entry->ip;
                int i;

                /* copy data from the end to avoid using extra buffer */
                for (i = entry->nr - 1; i >= 0; i--)
                        to[i] = (u64)(from[i]);
        }

        put_callchain_entry(rctx);

        return entry;
#else /* CONFIG_STACKTRACE */
        return NULL;
#endif
}

static long __bpf_get_stackid(struct bpf_map *map,
                              struct perf_callchain_entry *trace, u64 flags)
{
        struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
        struct stack_map_bucket *bucket, *new_bucket, *old_bucket;
        u32 hash, id, trace_nr, trace_len, i, max_depth;
        u32 skip = flags & BPF_F_SKIP_FIELD_MASK;
        bool user = flags & BPF_F_USER_STACK;
        u64 *ips;
        bool hash_matches;

        if (trace->nr <= skip)
                /* skipping more than usable stack trace */
                return -EFAULT;

        max_depth = stack_map_calculate_max_depth(map->value_size, stack_map_data_size(map), flags);
        trace_nr = min_t(u32, trace->nr - skip, max_depth - skip);
        trace_len = trace_nr * sizeof(u64);
        ips = trace->ip + skip;
        hash = jhash2((u32 *)ips, trace_len / sizeof(u32), 0);
        id = hash & (smap->n_buckets - 1);
        bucket = READ_ONCE(smap->buckets[id]);

        hash_matches = bucket && bucket->hash == hash;
        /* fast cmp */
        if (hash_matches && flags & BPF_F_FAST_STACK_CMP)
                return id;

        if (stack_map_use_build_id(map)) {
                struct bpf_stack_build_id *id_offs;

                /* for build_id+offset, pop a bucket before slow cmp */
                new_bucket = (struct stack_map_bucket *)
                        pcpu_freelist_pop(&smap->freelist);
                if (unlikely(!new_bucket))
                        return -ENOMEM;
                new_bucket->nr = trace_nr;
                id_offs = (struct bpf_stack_build_id *)new_bucket->data;
                for (i = 0; i < trace_nr; i++)
                        id_offs[i].ip = ips[i];
                stack_map_get_build_id_offset(id_offs, trace_nr, user, false /* !may_fault */);
                trace_len = trace_nr * sizeof(struct bpf_stack_build_id);
                if (hash_matches && bucket->nr == trace_nr &&
                    memcmp(bucket->data, new_bucket->data, trace_len) == 0) {
                        pcpu_freelist_push(&smap->freelist, &new_bucket->fnode);
                        return id;
                }
                if (bucket && !(flags & BPF_F_REUSE_STACKID)) {
                        pcpu_freelist_push(&smap->freelist, &new_bucket->fnode);
                        return -EEXIST;
                }
        } else {
                if (hash_matches && bucket->nr == trace_nr &&
                    memcmp(bucket->data, ips, trace_len) == 0)
                        return id;
                if (bucket && !(flags & BPF_F_REUSE_STACKID))
                        return -EEXIST;

                new_bucket = (struct stack_map_bucket *)
                        pcpu_freelist_pop(&smap->freelist);
                if (unlikely(!new_bucket))
                        return -ENOMEM;
                memcpy(new_bucket->data, ips, trace_len);
        }

        new_bucket->hash = hash;
        new_bucket->nr = trace_nr;

        old_bucket = xchg(&smap->buckets[id], new_bucket);
        if (old_bucket)
                pcpu_freelist_push(&smap->freelist, &old_bucket->fnode);
        return id;
}

BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,
           u64, flags)
{
        u32 elem_size = stack_map_data_size(map);
        bool user = flags & BPF_F_USER_STACK;
        struct perf_callchain_entry *trace;
        bool kernel = !user;
        u32 max_depth;

        if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK |
                               BPF_F_FAST_STACK_CMP | BPF_F_REUSE_STACKID)))
                return -EINVAL;

        max_depth = stack_map_calculate_max_depth(map->value_size, elem_size, flags);
        trace = get_perf_callchain(regs, kernel, user, max_depth,
                                   false, false, 0);

        if (unlikely(!trace))
                /* couldn't fetch the stack trace */
                return -EFAULT;

        return __bpf_get_stackid(map, trace, flags);
}

const struct bpf_func_proto bpf_get_stackid_proto = {
        .func           = bpf_get_stackid,
        .gpl_only       = true,
        .ret_type       = RET_INTEGER,
        .arg1_type      = ARG_PTR_TO_CTX,
        .arg2_type      = ARG_CONST_MAP_PTR,
        .arg3_type      = ARG_ANYTHING,
};

static __u64 count_kernel_ip(struct perf_callchain_entry *trace)
{
        __u64 nr_kernel = 0;

        while (nr_kernel < trace->nr) {
                if (trace->ip[nr_kernel] == PERF_CONTEXT_USER)
                        break;
                nr_kernel++;
        }
        return nr_kernel;
}

BPF_CALL_3(bpf_get_stackid_pe, struct bpf_perf_event_data_kern *, ctx,
           struct bpf_map *, map, u64, flags)
{
        struct perf_event *event = ctx->event;
        struct perf_callchain_entry *trace;
        bool kernel, user;
        __u64 nr_kernel;
        int ret;

        /* perf_sample_data doesn't have callchain, use bpf_get_stackid */
        if (!(event->attr.sample_type & PERF_SAMPLE_CALLCHAIN))
                return bpf_get_stackid((unsigned long)(ctx->regs),
                                       (unsigned long) map, flags, 0, 0);

        if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK |
                               BPF_F_FAST_STACK_CMP | BPF_F_REUSE_STACKID)))
                return -EINVAL;

        user = flags & BPF_F_USER_STACK;
        kernel = !user;

        trace = ctx->data->callchain;
        if (unlikely(!trace))
                return -EFAULT;

        nr_kernel = count_kernel_ip(trace);
        __u64 nr = trace->nr; /* save original */

        if (kernel) {
                trace->nr = nr_kernel;
                ret = __bpf_get_stackid(map, trace, flags);
        } else { /* user */
                u64 skip = flags & BPF_F_SKIP_FIELD_MASK;

                skip += nr_kernel;
                if (skip > BPF_F_SKIP_FIELD_MASK)
                        return -EFAULT;

                flags = (flags & ~BPF_F_SKIP_FIELD_MASK) | skip;
                ret = __bpf_get_stackid(map, trace, flags);
        }

        /* restore nr */
        trace->nr = nr;

        return ret;
}

const struct bpf_func_proto bpf_get_stackid_proto_pe = {
        .func           = bpf_get_stackid_pe,
        .gpl_only       = false,
        .ret_type       = RET_INTEGER,
        .arg1_type      = ARG_PTR_TO_CTX,
        .arg2_type      = ARG_CONST_MAP_PTR,
        .arg3_type      = ARG_ANYTHING,
};

static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
                            struct perf_callchain_entry *trace_in,
                            void *buf, u32 size, u64 flags, bool may_fault)
{
        u32 trace_nr, copy_len, elem_size, max_depth;
        bool user_build_id = flags & BPF_F_USER_BUILD_ID;
        bool crosstask = task && task != current;
        u32 skip = flags & BPF_F_SKIP_FIELD_MASK;
        bool user = flags & BPF_F_USER_STACK;
        struct perf_callchain_entry *trace;
        bool kernel = !user;
        int err = -EINVAL;
        u64 *ips;

        if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK |
                               BPF_F_USER_BUILD_ID)))
                goto clear;
        if (kernel && user_build_id)
                goto clear;

        elem_size = user_build_id ? sizeof(struct bpf_stack_build_id) : sizeof(u64);
        if (unlikely(size % elem_size))
                goto clear;

        /* cannot get valid user stack for task without user_mode regs */
        if (task && user && !user_mode(regs))
                goto err_fault;

        /* get_perf_callchain does not support crosstask user stack walking
         * but returns an empty stack instead of NULL.
         */
        if (crosstask && user) {
                err = -EOPNOTSUPP;
                goto clear;
        }

        max_depth = stack_map_calculate_max_depth(size, elem_size, flags);

        if (may_fault)
                rcu_read_lock(); /* need RCU for perf's callchain below */

        if (trace_in) {
                trace = trace_in;
                trace->nr = min_t(u32, trace->nr, max_depth);
        } else if (kernel && task) {
                trace = get_callchain_entry_for_task(task, max_depth);
        } else {
                trace = get_perf_callchain(regs, kernel, user, max_depth,
                                           crosstask, false, 0);
        }

        if (unlikely(!trace) || trace->nr < skip) {
                if (may_fault)
                        rcu_read_unlock();
                goto err_fault;
        }

        trace_nr = trace->nr - skip;
        copy_len = trace_nr * elem_size;

        ips = trace->ip + skip;
        if (user_build_id) {
                struct bpf_stack_build_id *id_offs = buf;
                u32 i;

                for (i = 0; i < trace_nr; i++)
                        id_offs[i].ip = ips[i];
        } else {
                memcpy(buf, ips, copy_len);
        }

        /* trace/ips should not be dereferenced after this point */
        if (may_fault)
                rcu_read_unlock();

        if (user_build_id)
                stack_map_get_build_id_offset(buf, trace_nr, user, may_fault);

        if (size > copy_len)
                memset(buf + copy_len, 0, size - copy_len);
        return copy_len;

err_fault:
        err = -EFAULT;
clear:
        memset(buf, 0, size);
        return err;
}

BPF_CALL_4(bpf_get_stack, struct pt_regs *, regs, void *, buf, u32, size,
           u64, flags)
{
        return __bpf_get_stack(regs, NULL, NULL, buf, size, flags, false /* !may_fault */);
}

const struct bpf_func_proto bpf_get_stack_proto = {
        .func           = bpf_get_stack,
        .gpl_only       = true,
        .ret_type       = RET_INTEGER,
        .arg1_type      = ARG_PTR_TO_CTX,
        .arg2_type      = ARG_PTR_TO_UNINIT_MEM,
        .arg3_type      = ARG_CONST_SIZE_OR_ZERO,
        .arg4_type      = ARG_ANYTHING,
};

BPF_CALL_4(bpf_get_stack_sleepable, struct pt_regs *, regs, void *, buf, u32, size,
           u64, flags)
{
        return __bpf_get_stack(regs, NULL, NULL, buf, size, flags, true /* may_fault */);
}

const struct bpf_func_proto bpf_get_stack_sleepable_proto = {
        .func           = bpf_get_stack_sleepable,
        .gpl_only       = true,
        .ret_type       = RET_INTEGER,
        .arg1_type      = ARG_PTR_TO_CTX,
        .arg2_type      = ARG_PTR_TO_UNINIT_MEM,
        .arg3_type      = ARG_CONST_SIZE_OR_ZERO,
        .arg4_type      = ARG_ANYTHING,
};

static long __bpf_get_task_stack(struct task_struct *task, void *buf, u32 size,
                                 u64 flags, bool may_fault)
{
        struct pt_regs *regs;
        long res = -EINVAL;

        if (!try_get_task_stack(task))
                return -EFAULT;

        regs = task_pt_regs(task);
        if (regs)
                res = __bpf_get_stack(regs, task, NULL, buf, size, flags, may_fault);
        put_task_stack(task);

        return res;
}

BPF_CALL_4(bpf_get_task_stack, struct task_struct *, task, void *, buf,
           u32, size, u64, flags)
{
        return __bpf_get_task_stack(task, buf, size, flags, false /* !may_fault */);
}

const struct bpf_func_proto bpf_get_task_stack_proto = {
        .func           = bpf_get_task_stack,
        .gpl_only       = false,
        .ret_type       = RET_INTEGER,
        .arg1_type      = ARG_PTR_TO_BTF_ID,
        .arg1_btf_id    = &btf_tracing_ids[BTF_TRACING_TYPE_TASK],
        .arg2_type      = ARG_PTR_TO_UNINIT_MEM,
        .arg3_type      = ARG_CONST_SIZE_OR_ZERO,
        .arg4_type      = ARG_ANYTHING,
};

BPF_CALL_4(bpf_get_task_stack_sleepable, struct task_struct *, task, void *, buf,
           u32, size, u64, flags)
{
        return __bpf_get_task_stack(task, buf, size, flags, true /* !may_fault */);
}

const struct bpf_func_proto bpf_get_task_stack_sleepable_proto = {
        .func           = bpf_get_task_stack_sleepable,
        .gpl_only       = false,
        .ret_type       = RET_INTEGER,
        .arg1_type      = ARG_PTR_TO_BTF_ID,
        .arg1_btf_id    = &btf_tracing_ids[BTF_TRACING_TYPE_TASK],
        .arg2_type      = ARG_PTR_TO_UNINIT_MEM,
        .arg3_type      = ARG_CONST_SIZE_OR_ZERO,
        .arg4_type      = ARG_ANYTHING,
};

BPF_CALL_4(bpf_get_stack_pe, struct bpf_perf_event_data_kern *, ctx,
           void *, buf, u32, size, u64, flags)
{
        struct pt_regs *regs = (struct pt_regs *)(ctx->regs);
        struct perf_event *event = ctx->event;
        struct perf_callchain_entry *trace;
        bool kernel, user;
        int err = -EINVAL;
        __u64 nr_kernel;

        if (!(event->attr.sample_type & PERF_SAMPLE_CALLCHAIN))
                return __bpf_get_stack(regs, NULL, NULL, buf, size, flags, false /* !may_fault */);

        if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK |
                               BPF_F_USER_BUILD_ID)))
                goto clear;

        user = flags & BPF_F_USER_STACK;
        kernel = !user;

        err = -EFAULT;
        trace = ctx->data->callchain;
        if (unlikely(!trace))
                goto clear;

        nr_kernel = count_kernel_ip(trace);

        if (kernel) {
                __u64 nr = trace->nr;

                trace->nr = nr_kernel;
                err = __bpf_get_stack(regs, NULL, trace, buf, size, flags, false /* !may_fault */);

                /* restore nr */
                trace->nr = nr;
        } else { /* user */
                u64 skip = flags & BPF_F_SKIP_FIELD_MASK;

                skip += nr_kernel;
                if (skip > BPF_F_SKIP_FIELD_MASK)
                        goto clear;

                flags = (flags & ~BPF_F_SKIP_FIELD_MASK) | skip;
                err = __bpf_get_stack(regs, NULL, trace, buf, size, flags, false /* !may_fault */);
        }
        return err;

clear:
        memset(buf, 0, size);
        return err;

}

const struct bpf_func_proto bpf_get_stack_proto_pe = {
        .func           = bpf_get_stack_pe,
        .gpl_only       = true,
        .ret_type       = RET_INTEGER,
        .arg1_type      = ARG_PTR_TO_CTX,
        .arg2_type      = ARG_PTR_TO_UNINIT_MEM,
        .arg3_type      = ARG_CONST_SIZE_OR_ZERO,
        .arg4_type      = ARG_ANYTHING,
};

/* Called from eBPF program */
static void *stack_map_lookup_elem(struct bpf_map *map, void *key)
{
        return ERR_PTR(-EOPNOTSUPP);
}

/* Called from syscall */
static int stack_map_lookup_and_delete_elem(struct bpf_map *map, void *key,
                                            void *value, u64 flags)
{
        return bpf_stackmap_extract(map, key, value, true);
}

/* Called from syscall */
int bpf_stackmap_extract(struct bpf_map *map, void *key, void *value,
                         bool delete)
{
        struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
        struct stack_map_bucket *bucket, *old_bucket;
        u32 id = *(u32 *)key, trace_len;

        if (unlikely(id >= smap->n_buckets))
                return -ENOENT;

        bucket = xchg(&smap->buckets[id], NULL);
        if (!bucket)
                return -ENOENT;

        trace_len = bucket->nr * stack_map_data_size(map);
        memcpy(value, bucket->data, trace_len);
        memset(value + trace_len, 0, map->value_size - trace_len);

        if (delete)
                old_bucket = bucket;
        else
                old_bucket = xchg(&smap->buckets[id], bucket);
        if (old_bucket)
                pcpu_freelist_push(&smap->freelist, &old_bucket->fnode);
        return 0;
}

static int stack_map_get_next_key(struct bpf_map *map, void *key,
                                  void *next_key)
{
        struct bpf_stack_map *smap = container_of(map,
                                                  struct bpf_stack_map, map);
        u32 id;

        WARN_ON_ONCE(!rcu_read_lock_held());

        if (!key) {
                id = 0;
        } else {
                id = *(u32 *)key;
                if (id >= smap->n_buckets || !smap->buckets[id])
                        id = 0;
                else
                        id++;
        }

        while (id < smap->n_buckets && !smap->buckets[id])
                id++;

        if (id >= smap->n_buckets)
                return -ENOENT;

        *(u32 *)next_key = id;
        return 0;
}

static long stack_map_update_elem(struct bpf_map *map, void *key, void *value,
                                  u64 map_flags)
{
        return -EINVAL;
}

/* Called from syscall or from eBPF program */
static long stack_map_delete_elem(struct bpf_map *map, void *key)
{
        struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
        struct stack_map_bucket *old_bucket;
        u32 id = *(u32 *)key;

        if (unlikely(id >= smap->n_buckets))
                return -E2BIG;

        old_bucket = xchg(&smap->buckets[id], NULL);
        if (old_bucket) {
                pcpu_freelist_push(&smap->freelist, &old_bucket->fnode);
                return 0;
        } else {
                return -ENOENT;
        }
}

/* Called when map->refcnt goes to zero, either from workqueue or from syscall */
static void stack_map_free(struct bpf_map *map)
{
        struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);

        bpf_map_area_free(smap->elems);
        pcpu_freelist_destroy(&smap->freelist);
        bpf_map_area_free(smap);
        put_callchain_buffers();
}

static u64 stack_map_mem_usage(const struct bpf_map *map)
{
        struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
        u64 value_size = map->value_size;
        u64 n_buckets = smap->n_buckets;
        u64 enties = map->max_entries;
        u64 usage = sizeof(*smap);

        usage += n_buckets * sizeof(struct stack_map_bucket *);
        usage += enties * (sizeof(struct stack_map_bucket) + value_size);
        return usage;
}

BTF_ID_LIST_SINGLE(stack_trace_map_btf_ids, struct, bpf_stack_map)
const struct bpf_map_ops stack_trace_map_ops = {
        .map_meta_equal = bpf_map_meta_equal,
        .map_alloc = stack_map_alloc,
        .map_free = stack_map_free,
        .map_get_next_key = stack_map_get_next_key,
        .map_lookup_elem = stack_map_lookup_elem,
        .map_lookup_and_delete_elem = stack_map_lookup_and_delete_elem,
        .map_update_elem = stack_map_update_elem,
        .map_delete_elem = stack_map_delete_elem,
        .map_check_btf = map_check_no_btf,
        .map_mem_usage = stack_map_mem_usage,
        .map_btf_id = &stack_trace_map_btf_ids[0],
};