linux-kernel - [PATCH v3 bpf] bpf: liveness: clarify get_outer_instance() handling in propagate_to_outer

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Message-Id: <20251021080849.860072-1-shardulsb08@gmail.com>
Date: Tue, 21 Oct 2025 13:38:46 +0530
From: Shardul Bankar <shardulsb08@...il.com>
To: bpf@...r.kernel.org
Cc: shardulsb08@...il.com,
	Eduard Zingerman <eddyz87@...il.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>,
	Stanislav Fomichev <sdf@...ichev.me>,
	Hao Luo <haoluo@...gle.com>,
	Jiri Olsa <jolsa@...nel.org>,
	linux-kernel@...r.kernel.org (open list)
Subject: [PATCH v3 bpf] bpf: liveness: clarify get_outer_instance() handling in propagate_to_outer_instance()

propagate_to_outer_instance() calls get_outer_instance() and uses the
returned pointer to reset and commit stack write marks. Under normal
conditions, update_instance() guarantees that an outer instance exists,
so get_outer_instance() cannot return an ERR_PTR.

However, explicitly checking for IS_ERR(outer_instance) makes this code
more robust and self-documenting. It reduces cognitive load when reading
the control flow and silences potential false-positive reports from
static analysis or automated tooling.

No functional change intended.

Reported-by: kernel-patches-review-bot (https://github.com/kernel-patches/bpf/pull/10006#issuecomment-3409419240)
Suggested-by: Eduard Zingerman <eddyz87@...il.com>
Signed-off-by: Shardul Bankar <shardulsb08@...il.com>
---
 kernel/bpf/liveness.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/bpf/liveness.c b/kernel/bpf/liveness.c
index 3c611aba7f52..ae31f9ee4994 100644
--- a/kernel/bpf/liveness.c
+++ b/kernel/bpf/liveness.c
@@ -522,6 +522,8 @@ static int propagate_to_outer_instance(struct bpf_verifier_env *env,
 
 	this_subprog_start = callchain_subprog_start(callchain);
 	outer_instance = get_outer_instance(env, instance);
+	if (IS_ERR(outer_instance))
+		return PTR_ERR(outer_instance);
 	callsite = callchain->callsites[callchain->curframe - 1];
 
 	reset_stack_write_marks(env, outer_instance, callsite);
-- 
2.34.1