linux-kernel - Re: [PATCH] perf: fix segfault in `lock contention -b`

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Message-ID: <aYO5iCWb3P_9YIVr@google.com>
Date: Wed, 4 Feb 2026 13:26:32 -0800
From: Namhyung Kim <namhyung@...nel.org>
To: Tycho Andersen <tycho@...nel.org>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	James Clark <james.clark@...aro.org>,
	Chun-Tse Shao <ctshao@...gle.com>, linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org, Ravi Bangoria <ravi.bangoria@....com>,
	K Prateek Nayak <kprateek.nayak@....com>
Subject: Re: [PATCH] perf: fix segfault in `lock contention -b`

Hello,

On Wed, Feb 04, 2026 at 08:20:34AM -0700, Tycho Andersen wrote:
> On Tue, Jan 13, 2026 at 01:18:52PM -0800, Namhyung Kim wrote:
> > On Mon, Jan 12, 2026 at 09:15:53AM -0700, Tycho Andersen wrote:
> > > On Fri, Jan 09, 2026 at 04:49:01PM -0800, Namhyung Kim wrote:
> > > > That said, can you add a NULL check in the init_numa_data() instead
> > > > and see how far it can go?
> > > 
> > > Looks like not much further, it fails in lock_contention_bpf__load():
> > > 
> > > ./perf lock contention -b
> > > libbpf: kernel BTF is missing at '/sys/kernel/btf/vmlinux', was CONFIG_DEBUG_INFO_BTF enabled?
> > > libbpf: failed to find valid kernel BTF
> > > libbpf: kernel BTF is missing at '/sys/kernel/btf/vmlinux', was CONFIG_DEBUG_INFO_BTF enabled?
> > > libbpf: failed to find valid kernel BTF
> > > libbpf: Error loading vmlinux BTF: -ESRCH
> > > libbpf: failed to load BPF skeleton 'lock_contention_bpf': -ESRCH
> > > Failed to load lock-contention BPF skeleton
> > > lock contention BPF setup failed
> > 
> > Thanks for checking this.  I think it's ok to fail like this when BTF is
> > not enabled.  Let me see if I can make some changes to run without it
> > later.
> 
> Gentle ping, I was just reminded of this crash again this morning.

Sorry for the delay.  Please send a fix with the NULL check in the
init_numa_data().  I think it'd be simpler and easier to improve.

Thanks,
Namhyung