Subject: Re: VRF and/or cgroups problem on Fedora-30, 5.2.21+ kernel

From: Ben Greear <[email-masked]>
Date: Tue, 26 Nov 2019 09:36:57 -0800

On 11/25/2019 12:53 PM, David Ahern wrote:
> On 11/25/19 10:35 AM, Ben Greear wrote:
>>>> And surely 'ip' could output a better error than just 'permission
>>>> denied' for
>>>> this error case?  Or even something that would show up in dmesg to give
>>>> a clue?
>>>
>>> That error comes from the bpf syscall:
>>>
>>> bpf(BPF_PROG_LOAD, {prog_type=BPF_PROG_TYPE_CGROUP_SOCK, insn_cnt=6,
>>> insns=0x7ffc8e5d1e00, license="GPL", log_level=1, log_size=262144,
>>> log_buf="", kern_version=KERNEL_VERSION(0, 0, 0), prog_flags=0,
>>> prog_name="", prog_ifindex=0,
>>> expected_attach_type=BPF_CGROUP_INET_INGRESS, prog_btf_fd=0,
>>> func_info_rec_size=0, func_info=NULL, func_info_cnt=0,
>>> line_info_rec_size=0, line_info=NULL, line_info_cnt=0}, 112) = -1 EPERM
>>> (Operation not permitted)
>>
>> So, we can change iproute/lib/bpf.c to print a suggestion to increase
>> locked memory
>> if this returns EPERM?
>>
>
> looks like SYS_ADMIN and locked memory are the -EPERM failures.
>
> I do not see any API that returns user->locked_vm, only per-task
> locked_vm. Knowing that number would help a lot in understanding proper
> system settings.
>
> Running 'perf record' while trying to do 'ip vrf exec' is an easy way to
> hit the locked memory exceeded error. We could add a hint to iproute2.
> Something like:
>
> diff --git a/ip/ipvrf.c b/ip/ipvrf.c
> index b9a43675cbd6..15637924f31a 100644
> --- a/ip/ipvrf.c
> +++ b/ip/ipvrf.c
> @@ -281,9 +281,16 @@ static int vrf_configure_cgroup(const char *path,
> int ifindex)
>                  fprintf(stderr, "Failed to load BPF prog: '%s'\n",
>                          strerror(errno));
>
> -               if (errno != EPERM) {
> +               if (errno == EPERM) {
> +                       if (geteuid() != 0)
> +                               fprintf(stderr,
> +                                       "Hint: Must run as root to set
> VRF.\n");
> +                       else
> +                               fprintf(stderr,
> +                                       "Hint: Most likely locked memory
> threshold exceeded. Increase 'ulimit -l'\n");

I think I would suggest 'ulimit -l 1024'.  Advanced users can try different
values if they care or have super tight memory constraints, but most users could
probably get benefit from the suggestion.

Thanks,
Ben

> +               } else {
>                          fprintf(stderr,
> -                               "Kernel compiled with CGROUP_BPF
> enabled?\n");
> +                               "Hint: Kernel compiled with CGROUP_BPF
> enabled?\n");
>                  }
>                  goto out;
>          }
>

-- 
Ben Greear <[email-masked]>
Candela Technologies Inc  http://www.candelatech.com