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.
Whether or not this is something worth addressing I don't know.
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