On 2023-07-28 22:12, Michael Weiß wrote:
> 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! Patch applied.
<https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=ec32926e9b5aa37c4c40fc8c09497cf2a50560a7>
Cheers,
Alex
>
> Thanks,
> Michael
>
>> In this case, just call
>> .BR bpf ()
>> again with the same parameters.
>>
>>
>>> .B EBADF
>>> .I fd
>>> is not an open file descriptor.
>>
--
<http://www.alejandro-colomar.es/>
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