linux-kernel - [PATCH bpf-next] bpf: Don't use idx variable when registering kfunc dtors

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Date:   Wed, 23 Nov 2022 07:52:53 -0600
From:   David Vernet <void@...ifault.com>
To:     bpf@...r.kernel.org
Cc:     ast@...nel.org, andrii@...nel.org, daniel@...earbox.net,
        martin.lau@...ux.dev, yhs@...com, song@...nel.org, sdf@...gle.com,
        john.fastabend@...il.com, kpsingh@...nel.org, jolsa@...nel.org,
        haoluo@...gle.com, tj@...nel.org, kernel-team@...com,
        linux-kernel@...r.kernel.org, kernel test robot <lkp@...el.com>
Subject: [PATCH bpf-next] bpf: Don't use idx variable when registering kfunc dtors

In commit fda01efc6160 ("bpf: Enable cgroups to be used as kptrs"), I
added an 'int idx' variable to kfunc_init() which was meant to
dynamically set the index of the btf id entries of the
'generic_dtor_ids' array. This was done to make the code slightly less
brittle as the struct cgroup * kptr kfuncs such as bpf_cgroup_aquire()
are compiled out if CONFIG_CGROUPS is not defined. This, however, causes
an lkp build warning:

>> kernel/bpf/helpers.c:2005:40: warning: multiple unsequenced
   modifications to 'idx' [-Wunsequenced]
	.btf_id       = generic_dtor_ids[idx++],

Fix the warning by just hard-coding the indices.

Fixes: fda01efc6160 ("bpf: Enable cgroups to be used as kptrs")
Reported-by: kernel test robot <lkp@...el.com>
Signed-off-by: David Vernet <void@...ifault.com>
---
 kernel/bpf/helpers.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index e4e9db301db5..da2681ebb7c3 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2019,16 +2019,16 @@ static const struct btf_kfunc_id_set common_kfunc_set = {
 
 static int __init kfunc_init(void)
 {
-	int ret, idx = 0;
+	int ret;
 	const struct btf_id_dtor_kfunc generic_dtors[] = {
 		{
-			.btf_id       = generic_dtor_ids[idx++],
-			.kfunc_btf_id = generic_dtor_ids[idx++]
+			.btf_id       = generic_dtor_ids[0],
+			.kfunc_btf_id = generic_dtor_ids[1]
 		},
 #ifdef CONFIG_CGROUPS
 		{
-			.btf_id       = generic_dtor_ids[idx++],
-			.kfunc_btf_id = generic_dtor_ids[idx++]
+			.btf_id       = generic_dtor_ids[2],
+			.kfunc_btf_id = generic_dtor_ids[3]
 		},
 #endif
 	};
-- 
2.38.1