Re: [PATCH RFC bpf-next v3 07/16] bpf/helpers: mark the callback of bpf_timer_set_sleepable_cb() as sleepable

On Wed, 2024-02-21 at 17:25 +0100, Benjamin Tissoires wrote:

[...]

@@ -626,6 +627,7 @@ struct bpf_subprog_info { bool is_async_cb: 1; bool is_exception_cb: 1; bool args_cached: 1;

• bool is_sleepable: 1;

u8 arg_cnt; struct bpf_subprog_arg_info args[MAX_BPF_FUNC_REG_ARGS];

[...]

@@ -2421,6 +2424,7 @@ static struct bpf_verifier_state *push_async_cb(struct bpf_verifier_env *env, * Initialize it similar to do_check_common(). */ elem->st.branches = 1;

• elem->st.in_sleepable = env->subprog_info[subprog].is_sleepable; frame = kzalloc(sizeof(*frame), GFP_KERNEL); if (!frame) goto err;

[...]

@@ -9478,6 +9483,7 @@ static int push_callback_call(struct bpf_verifier_env *env, struct bpf_insn *ins /* there is no real recursion here. timer callbacks are async */ env->subprog_info[subprog].is_async_cb = true;

• env->subprog_info[subprog].is_sleepable = is_bpf_timer_set_sleepable_cb_kfunc(insn->imm);
  

  async_cb = push_async_cb(env, env->subprog_info[subprog].start, insn_idx, subprog);

I'd make is_sleepable a parameter for push_async_cb() instead of a field in struct bpf_subprog_info. I had to spend some time convincing myself that bpf_subprog_info->is_sleepable does not have to be computed before do_check() in check_cfg(), or what would happen if same callback is passed as both sleepable and non-sleepable callback. These questions won't arise if this is a parameter.

[...]