On Mon, Apr 8, 2024 at 3:36 PM Eduard Zingerman eddyz87@gmail.com wrote:
On Mon, 2024-04-08 at 10:09 +0200, Benjamin Tissoires wrote:
Now that we have bpf_timer_set_sleepable_cb() available and working, we can tag the attached callback as sleepable, and let the verifier check in the correct context the calls and kfuncs.
Signed-off-by: Benjamin Tissoires bentiss@kernel.org
I think this patch is fine with one nit regarding in_sleepable(). Acked-by: Eduard Zingerman eddyz87@gmail.com
@@ -5279,7 +5281,8 @@ static int map_kptr_match_type(struct bpf_verifier_env *env,
static bool in_sleepable(struct bpf_verifier_env *env) {
return env->prog->sleepable;
return env->prog->sleepable ||(env->cur_state && env->cur_state->in_sleepable);}
Sorry, I already raised this before. As far as I understand the 'env->cur_state' check is needed because this function is used from do_misc_fixups():
if (is_storage_get_function(insn->imm)) { if (!in_sleepable(env) || env->insn_aux_data[i + delta].storage_get_func_atomic) insn_buf[0] = BPF_MOV64_IMM(BPF_REG_5, (__force __s32)GFP_ATOMIC); else insn_buf[0] = BPF_MOV64_IMM(BPF_REG_5, (__force __s32)GFP_KERNEL); insn_buf[1] = *insn; cnt = 2; ... }For a timer callback function 'env->prog->sleepable' would be false. Which means that inside sleepable callback function GFP_ATOMIC would be used in cases where GFP_KERNEL would be sufficient. An alternative would be to check (and set) sleepable flag not for a full program but for a subprogram.
At this point all subprograms are still part of the main program. jit_subprogs() hasn't been called yet. So there is only one 'prog' object. So cannot really set prog->sleepable for callback subprog.
But you've raised a good point. We can remove "!in_sleepable(env)" part in do_misc_fixups() with: - if (in_sleepable(env) && is_storage_get_function(func_id)) - env->insn_aux_data[insn_idx].storage_get_func_atomic = true;
+ if (is_storage_get_function(func_id)) + env->insn_aux_data[insn_idx].storage_get_func_atomic = !in_sleepable(env);