bpf: Print some info if disable bpf_jit_enable failed

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>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/1652153703-22729-3-git-send-email-yangtiezhu@loongson.cn

diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index cf00dd7..ca4527f 100644 (file)
--- 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;
 
        if (write && !capable(CAP_SYS_ADMIN))
@@ -283,6 +285,10 @@ static int proc_dointvec_minmax_bpf_enable(struct ctl_table *table, int write,
                        ret = -EPERM;
                }
        }
+
+       if (write && ret && min == max)
+               pr_info_once("CONFIG_BPF_JIT_ALWAYS_ON is enabled, bpf_jit_enable is permanently set to 1.\n");
+
        return ret;
 }