Hi Alex,
On 28.07.23 21:42, Alejandro Colomar wrote:
> Hi Michael, Alexei,
>
> On 2023-07-21 14:06, Michael Weiß wrote:
>> Since commit c3494801cd1785e2 ("bpf: check pending signals while
>> verifying programs", bpf() may also fail with EAGAIN if the verifier
>> detects pending signals.
>>
>> This was triggered in the cmld of GyroidOS when loading a cgroups
>> device program during container start. We had a look in the man page
>> and where confused that EAGAIN was not listed as possible error.
>> Digging in the kernel source revealed the EAGAIN in the verifier
>> introduced by the commit above. Further investigation showed that
>> libbpf already wraps that case, by a retry loop.
>>
>> Since GyroidOS uses the system call directly and not libbpf, we missed
>> to handle this error correctly. Thus, this hint in the man page for
>> the bpf() system call should be helpful for others who implement on
>> the low-level interface, too.
>>
>> Signed-off-by: Michael Weiß <michael.weiss@xxxxxxxxxxxxxxxxxxx>
>
> Thanks for the patch! I find a few sentences have some minor wording
> issues. I'll propose a small change to your proposal. Please check.
> If you confirm it, I'll amend your commit, so you don't need to resend.
> See below
>
> Cheers,
> Alex
>
>> ---
>> man2/bpf.2 | 10 ++++++++++
>> 1 file changed, 10 insertions(+)
>>
>> diff --git a/man2/bpf.2 b/man2/bpf.2
>> index d32435a1d..7cef7f24d 100644
>> --- a/man2/bpf.2
>> +++ b/man2/bpf.2
>> @@ -991,6 +991,16 @@ and examine
>> .I log_buf
>> for the specific reason provided by the verifier.
>> .TP
>> +.B EAGAIN
>> +For
>> +.BR BPF_PROG_LOAD ,
>> +indicates that needed resources are blocked.
>> +This is due to the verifier detects pending signals while it is checking
>> +the bpf program about its validity.
>> +In this case, just call
>> +.BR bpf ()
>> +again with the same parameters.
>> +.TP
>
> diff --git a/man2/bpf.2 b/man2/bpf.2
> index 7cef7f24d..ea68e1293 100644
> --- a/man2/bpf.2
> +++ b/man2/bpf.2
> @@ -995,8 +995,8 @@ .SH ERRORS
> For
> .BR BPF_PROG_LOAD ,
> indicates that needed resources are blocked.
> -This is due to the verifier detects pending signals while it is checking
> -the bpf program about its validity.
> +This happens when the verifier detects pending signals
> +while it is checking the validity of the bpf program.
Sounds good, confirmed.
Thanks,
Michael
> In this case, just call
> .BR bpf ()
> again with the same parameters.
>
>
>> .B EBADF
>> .I fd
>> is not an open file descriptor.
>
