Re: perf test case 40 LLVM search and compile runs endless (eBPF linkage issue)

From: Arnaldo Carvalho de Melo <acme@kernel.org>
To: Jiri Olsa <olsajiri@gmail.com>
Cc: Thomas Richter <tmricht@linux.ibm.com>,
	"linux-perf-use." <linux-perf-users@vger.kernel.org>,
	Jiri Olsa <jolsa@redhat.com>,
	Sumanth Korikkar <sumanthk@linux.ibm.com>,
	Heiko Carstens <hca@linux.ibm.com>,
	vasily Gorbik <gor@linux.ibm.com>,
	Ian Rogers <irogers@google.com>,
	Ilya Leoshkevich <iii@linux.ibm.com>,
	Sven Schnelle <svens@linux.ibm.com>
Subject: Re: perf test case 40 LLVM search and compile runs endless (eBPF linkage issue)
Date: Tue, 24 May 2022 11:33:35 -0300	[thread overview]
Message-ID: <Yozsvxx0JsTbVgW1@kernel.org> (raw)
In-Reply-To: <YozLKby7ITEtchC9@krava>

Em Tue, May 24, 2022 at 02:10:17PM +0200, Jiri Olsa escreveu:
> On Mon, May 23, 2022 at 01:09:51PM +0200, Jiri Olsa wrote:
> > On Mon, May 23, 2022 at 12:52:06PM +0200, Thomas Richter wrote:
> > > On s390 the test case 40 'LLVM search and compile' runs for ever:
> > > 
> > >   # date; timeout 30s perf test -F 40; date
> > >   Mon May 23 12:35:48 PM CEST 2022
> > >    40: LLVM search and compile   :
> > >    40.1: Basic BPF llvm compile  :
> > >   Mon May 23 12:36:18 PM CEST 2022
> > >   #
> > > 
> > > Investigation by Ilya Leoshkevich revealed:
> > > On s390 we hit an endless loop where bpf_object__next_program and bpf_program__next 
> > > infinitely call each other. We tracked this down to ld.so preferring the perf's 
> > > bpf_object__next_program weak copy over the libbpf's strong one.
> > > 
> > > This is introduced with commit 2a4898fc264a ("perf tools: Add more weak libbpf functions")
> > > 
> > > Also see discussion in 
> > > https://lore.kernel.org/lkml/YY%2FAR2Dcaws0BAE9@kernel.org/
> > > 
> > > How can this be fixed asap? Thanks a lot.
> > 
> > I was just suggesting to remove that:
> >   https://lore.kernel.org/bpf/Yos8hq3NmBwemoJw@krava/T/#mda8abccbf475b99d25abe5498a5df1af2da82ee8
> > 
> > it's no longer needed and can cause problem apparently
> 
> after discussing with Arnaldo we decided to go for another fix,
> could you please try this branch:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git
>   perf/weak

I'm adding comments, testing and applying that series in my local tree,
so far so good, will push to tmp.perf/core later.

Please let us know if you guys looked at the patches in Jiri's perf/weak
branch and if you are ok with it so that I can add
Tested-by/acked-by/reviewed-by, which are always more than welcome.

Thanks,

- Arnaldo