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From:   Tiezhu Yang <yangtiezhu@loongson.cn>
To:     davem@davemloft.net, Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>
Cc:     netdev@vger.kernel.org, bpf@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH bpf-next 3/3] bpf: Print some info if disable bpf_jit_enable failed
Date:   Mon,  9 May 2022 14:57:55 +0800
Message-Id: <1652079475-16684-4-git-send-email-yangtiezhu@loongson.cn>
In-Reply-To: <1652079475-16684-1-git-send-email-yangtiezhu@loongson.cn>
References: <1652079475-16684-1-git-send-email-yangtiezhu@loongson.cn>
Precedence: bulk

A user told me that bpf_jit_enable can be disabled on one system, but he
failed to disable bpf_jit_enable on the other system:

  # echo 0 > /proc/sys/net/core/bpf_jit_enable
  bash: echo: write error: Invalid argument

No useful info is available through the dmesg log, a quick analysis shows
that the issue is related with CONFIG_BPF_JIT_ALWAYS_ON.

When CONFIG_BPF_JIT_ALWAYS_ON is enabled, bpf_jit_enable is permanently set
to 1 and setting any other value than that will return failure.

It is better to print some info to tell the user if disable bpf_jit_enable
failed.

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
---
 net/core/sysctl_net_core.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index 059352b..f8a1d450 100644
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -266,6 +266,8 @@ static int proc_dointvec_minmax_bpf_enable(struct ctl_table *table, int write,
 					   loff_t *ppos)
 {
 	int ret, jit_enable = *(int *)table->data;
+	int min = *(int *)table->extra1;
+	int max = *(int *)table->extra2;
 	struct ctl_table tmp = *table;
 
 	tmp.data = &jit_enable;
@@ -280,6 +282,10 @@ static int proc_dointvec_minmax_bpf_enable(struct ctl_table *table, int write,
 			ret = -EPERM;
 		}
 	}
+
+	if (write && ret && min == max)
+		pr_info("CONFIG_BPF_JIT_ALWAYS_ON is enabled, bpf_jit_enable is permanently set to 1.\n");
+
 	return ret;
 }
 
-- 
2.1.0