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Date: Wed, 4 Feb 2026 13:26:32 -0800
From: Namhyung Kim <namhyung@kernel.org>
To: Tycho Andersen <tycho@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>, Mark Rutland <mark.rutland@arm.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Jiri Olsa <jolsa@kernel.org>, Ian Rogers <irogers@google.com>,
	Adrian Hunter <adrian.hunter@intel.com>,
	James Clark <james.clark@linaro.org>,
	Chun-Tse Shao <ctshao@google.com>, linux-perf-users@vger.kernel.org,
	linux-kernel@vger.kernel.org, Ravi Bangoria <ravi.bangoria@amd.com>,
	K Prateek Nayak <kprateek.nayak@amd.com>
Subject: Re: [PATCH] perf: fix segfault in `lock contention -b`
Message-ID: <aYO5iCWb3P_9YIVr@google.com>
References: <20260109164417.396138-1-tycho@kernel.org>
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 <aWUeOQbFOZ2CVBG2@tycho.pizza>
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In-Reply-To: <aYNjwvYkvk0Ul2Jl@tycho.pizza>

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