Re: dumpcap: weird failure with six IPv6 hosts in the filter

[Stephen Hemminger <stephen@networkplumber.org>]

On Mon, 17 Jun 2024 23:43:19 +0300
Isaac Boukris <iboukris@gmail.com> wrote:

> On Mon, Jun 17, 2024 at 10:37 PM Isaac Boukris <iboukris@gmail.com> wrote:
> >  
> > > Just a quick update that I still see the issue in my env with the
> > > master branch (24.07.0-rc0), I'm now testing by adding the filter to
> > > 'sample_filters' in test_bpf.c and running:
> > > time sudo build/app/dpdk-test bpf_convert_autotest
> > >
> > > With 5 hosts it takes less than 2 secs, with 6 it takes about 25 secs,
> > > i'll try to strace it maybe.  
> >
> > strace was useless, no syscalls for ~18 secs, not sure how to debug it
> > further, valgrind / callgrind don't work on dpdk..
> >
> > It doesn't seem to be about the size though, I was able to produce
> > larger bpf code with ipv4 addresses and it worked fine too.  
> 
> Debugged a bit further with gdb, it looks like it is stuck in a while
> loop in lib/bpf/bpf_validate.c:evaluate(), there is a comment saying
> "make sure we evaluate each node only once" but it seem to go back and
> forth on the same idx's afaict.

No idea, only original author understands the verifier.
Having our own unique verifier may not be a good idea.
There some other userspace BPF projects, seems like a good place for
convergence.


https://lpc.events/event/17/contributions/1639/attachments/1280/2585/userspace-ebpf-bpftime-lpc.pdf