Re: [PATCH v2] perf: fix segfault in `lock contention -b`

[Namhyung Kim]

Hello,

On Thu, Feb 05, 2026 at 09:32:50AM -0700, Tycho Andersen wrote:
> From: "Tycho Andersen (AMD)" <tycho@xxxxxxxxxx>
> 
> When run on a kernel without BTF info, perf crashes:
> 
>     libbpf: kernel BTF is missing at '/sys/kernel/btf/vmlinux', was CONFIG_DEBUG_INFO_BTF enabled?
>     libbpf: failed to find valid kernel BTF
> 
>     Program received signal SIGSEGV, Segmentation fault.
>     0x00005555556915b7 in btf.type_cnt ()
>     (gdb) bt
>     #0  0x00005555556915b7 in btf.type_cnt ()
>     #1  0x0000555555691fbc in btf_find_by_name_kind ()
>     #2  0x00005555556920d0 in btf.find_by_name_kind ()
>     #3  0x00005555558a1b7c in init_numa_data (con=0x7fffffffd0a0) at util/bpf_lock_contention.c:125
>     #4  0x00005555558a264b in lock_contention_prepare (con=0x7fffffffd0a0) at util/bpf_lock_contention.c:313
>     #5  0x0000555555620702 in __cmd_contention (argc=0, argv=0x7fffffffea10) at builtin-lock.c:2084
>     #6  0x0000555555622c8d in cmd_lock (argc=0, argv=0x7fffffffea10) at builtin-lock.c:2755
>     #7  0x0000555555651451 in run_builtin (p=0x555556104f00 <commands+576>, argc=3, argv=0x7fffffffea10)
>         at perf.c:349
>     #8  0x00005555556516ed in handle_internal_command (argc=3, argv=0x7fffffffea10) at perf.c:401
>     #9  0x000055555565184e in run_argv (argcp=0x7fffffffe7fc, argv=0x7fffffffe7f0) at perf.c:445
>     #10 0x0000555555651b9f in main (argc=3, argv=0x7fffffffea10) at perf.c:553
> 
> Check if btf loading failed, and don't do anything with it in
> init_numa_data(). This leads to the following error message, instead of
> just a crash:
> 
>     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
> 
> Signed-off-by: Tycho Andersen (AMD) <tycho@xxxxxxxxxx>
> CC: Ravi Bangoria <ravi.bangoria@xxxxxxx>
> CC: K Prateek Nayak <kprateek.nayak@xxxxxxx>

Acked-by: Namhyung Kim <namhyung@xxxxxxxxxx>

Thanks,
Namhyung

> ---
>  tools/perf/util/bpf_lock_contention.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/tools/perf/util/bpf_lock_contention.c b/tools/perf/util/bpf_lock_contention.c
> index 7b5671f13c53..8cd991b3f209 100644
> --- a/tools/perf/util/bpf_lock_contention.c
> +++ b/tools/perf/util/bpf_lock_contention.c
> @@ -117,6 +117,9 @@ static void init_numa_data(struct lock_contention *con)
>  	long last = -1;
>  	int ret;
>  
> +	if (!con->btf)
> +		return;
> +
>  	/*
>  	 * 'struct zone' is embedded in 'struct pglist_data' as an array.
>  	 * As we may not have full information of the struct zone in the
> 
> base-commit: 18f7fcd5e69a04df57b563360b88be72471d6b62
> -- 
> 2.52.0
>