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// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
#include <vmlinux.h>
#include <bpf/bpf_helpers.h>
char _license[] SEC("license") = "GPL";
/* rh is not at offset 0, so the callback's value recovery is exercised. */
struct elem {
__u64 pad;
struct bpf_rcu_head rh;
__u64 val;
};
struct {
__uint(type, BPF_MAP_TYPE_ARRAY);
__uint(max_entries, 2);
__type(key, __u32);
__type(value, struct elem);
} arr SEC(".maps");
__u32 cb_key;
__u64 cb_keys;
__u64 cb_val;
__u32 cb_max_entries;
int callbacks;
int arm_err;
int busy_err;
int chain; /* set by userspace: number of times to re-arm from the callback */
int chain_err;
static int reclaim(struct bpf_map *map, void *key, void *value)
{
struct elem *e = value;
cb_key = *(__u32 *)key;
__sync_fetch_and_or(&cb_keys, 1ULL << cb_key);
cb_val = e->val;
cb_max_entries = map->max_entries;
e->val = 0;
if (chain > 0) {
chain--;
chain_err = bpf_call_rcu(&e->rh, &arr, reclaim);
}
__sync_fetch_and_add(&callbacks, 1);
return 0;
}
SEC("syscall")
int arm(void *ctx)
{
__u32 key = 1;
struct elem *e;
e = bpf_map_lookup_elem(&arr, &key);
if (!e)
return 1;
e->val = 0xdeadbeef;
/* Keep a grace period from elapsing between the two arms. */
bpf_rcu_read_lock();
arm_err = bpf_call_rcu(&e->rh, &arr, reclaim);
busy_err = bpf_call_rcu(&e->rh, &arr, reclaim);
bpf_rcu_read_unlock();
return 0;
}
SEC("syscall")
int arm_both(void *ctx)
{
__u32 key0 = 0, key1 = 1;
struct elem *e0, *e1;
e0 = bpf_map_lookup_elem(&arr, &key0);
e1 = bpf_map_lookup_elem(&arr, &key1);
if (!e0 || !e1)
return 1;
e0->val = 0xdeadbeef;
e1->val = 0xdeadbeef;
arm_err = bpf_call_rcu(&e0->rh, &arr, reclaim);
arm_err |= bpf_call_rcu(&e1->rh, &arr, reclaim);
return 0;
}
SEC("syscall")
int arm_trace(void *ctx)
{
__u32 key = 1;
struct elem *e;
e = bpf_map_lookup_elem(&arr, &key);
if (!e)
return 1;
e->val = 0xdeadbeef;
/* No lock needed: the enclosing rcu_read_lock_trace() already blocks the grace period. */
arm_err = bpf_call_rcu_tasks_trace(&e->rh, &arr, reclaim);
busy_err = bpf_call_rcu_tasks_trace(&e->rh, &arr, reclaim);
return 0;
}
SEC("iter/bpf_map_elem")
int dump(struct bpf_iter__bpf_map_elem *ctx)
{
return 0;
}
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