linux-kernel - [PATCH RFC bpf-next 1/8] bpf: ignore sleepable prog parameter for kfuncs

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Message-Id: <20240507-bpf_async-v1-1-b4df966096d8@kernel.org>
Date: Tue, 07 May 2024 15:19:29 +0200
From: Benjamin Tissoires <bentiss@...nel.org>
To: Alexei Starovoitov <ast@...nel.org>, 
 Daniel Borkmann <daniel@...earbox.net>, 
 John Fastabend <john.fastabend@...il.com>, 
 Andrii Nakryiko <andrii@...nel.org>, 
 Martin KaFai Lau <martin.lau@...ux.dev>, 
 Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
 Yonghong Song <yonghong.song@...ux.dev>, KP Singh <kpsingh@...nel.org>, 
 Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>, 
 Jiri Olsa <jolsa@...nel.org>, Mykola Lysenko <mykolal@...com>, 
 Shuah Khan <shuah@...nel.org>
Cc: bpf@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-kselftest@...r.kernel.org, Benjamin Tissoires <bentiss@...nel.org>
Subject: [PATCH RFC bpf-next 1/8] bpf: ignore sleepable prog parameter for
 kfuncs

There is no change of behavior: for each kfunc, we store the prog
sleepable state. But this allows to declare an async non sleepable
callback from a syscall, where everything is sleepable.

Signed-off-by: Benjamin Tissoires <bentiss@...nel.org>

---

This is an RFC, and is not meant to be fully reviewed/applied as it is.
I'm posting this to show what I wanted to explain in
https://lore.kernel.org/bpf/mhkzkf4e23uvljtmwizwcxyuyat2tmfxn33xb4t7waafgmsa66@mcrzpj3b6ssx/
---
 kernel/bpf/verifier.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 5d42db05315e..856cb77d0f87 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5288,8 +5288,7 @@ static int map_kptr_match_type(struct bpf_verifier_env *env,
 
 static bool in_sleepable(struct bpf_verifier_env *env)
 {
-	return env->prog->sleepable ||
-	       (env->cur_state && env->cur_state->in_sleepable);
+	return env->cur_state ? env->cur_state->in_sleepable : env->prog->sleepable;
 }
 
 /* The non-sleepable programs and sleepable programs with explicit bpf_rcu_read_lock()
@@ -20722,6 +20721,7 @@ static int do_check_common(struct bpf_verifier_env *env, int subprog)
 	state->curframe = 0;
 	state->speculative = false;
 	state->branches = 1;
+	state->in_sleepable = env->prog->sleepable;
 	state->frame[0] = kzalloc(sizeof(struct bpf_func_state), GFP_KERNEL);
 	if (!state->frame[0]) {
 		kfree(state);

-- 
2.44.0