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    Subject[PATCH bpf-next 3/3] bpf: Print some info if disable bpf_jit_enable failed
    Date
    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
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