From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 72A2B23ED6A; Mon, 12 Jan 2026 16:15:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768234557; cv=none; b=QcvH9xqPnLaPlI0Nisz/J4VBWaISTwCZbEfSo1YxjGVtRSP24pwnxRju5/hJ+rYPifUj4jdOu/IlzodVtKmohczte/+IB40mPS4+H/rVdICsV+h+zfbylx8Y3yliu8xOQuvkpqLhOGG5mfWI7ubtgu3KEgtck3GYzouz36LL8dM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768234557; c=relaxed/simple; bh=eI8C8BtDMPqSFRxHRe5KQNURmveRuV+sdj74r3IkIyM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=G+lG5X9hip+piF9UN2Pmfsw9JrzRZsNMK2IrY2AFMDmtDSyFNegcMmi2AjuRip5KxSFYN1Tg7gNqS+ZooGXtNyNlXYKZMJr5f4g91bHToMYGtJyq/EgjVNC/xxVq7zc9WsZec4o2GfSvq/S9pJxIvPHPtZjSQxTy07oz/WLIpDc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=DnvYy0hN; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="DnvYy0hN" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 73D58C116D0; Mon, 12 Jan 2026 16:15:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1768234557; bh=eI8C8BtDMPqSFRxHRe5KQNURmveRuV+sdj74r3IkIyM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=DnvYy0hN/8mVEw+0u+XM+aMPj1rLiTn5BKzlaPyMAPqnObPQpJF0Zxzv/hnEWGDQx o0AtIYw1N3tBsnyGcD3vaytaTepZHnhxh4DHZrvldB1paSDSDi3PX7tg8YcdHY3SBw qdcvW3+vXHgSf/VK1T/M9HZuuBpifTAoBJaIVlH/cZESvB2wiUUKqGNiLCoY8zPhT6 B7PTzN0ggIKP2oALcwwWthdNl8PK+GZRd/lCVe6UL11R7yIPK7m1YTYRLYjtvlk2Ck UZxM7fjocWwNetgUPpw14c/DMv1G2VkuQJvp8qL2CxR/cjYcgAY3oFwUl/gO8/Bv8R j/rhE5/imOw4Q== Date: Mon, 12 Jan 2026 09:15:53 -0700 From: Tycho Andersen To: Namhyung Kim Cc: Arnaldo Carvalho de Melo , Peter Zijlstra , Ingo Molnar , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , James Clark , Chun-Tse Shao , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, Ravi Bangoria , K Prateek Nayak Subject: Re: [PATCH] perf: fix segfault in `lock contention -b` Message-ID: References: <20260109164417.396138-1-tycho@kernel.org> Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Fri, Jan 09, 2026 at 04:49:01PM -0800, Namhyung Kim wrote: > On Fri, Jan 09, 2026 at 09:44:17AM -0700, Tycho Andersen wrote: > > From: "Tycho Andersen (AMD)" > > > > When run on a kernel without BTF info, I get: > > > > 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 , 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 > > > > If we really are running -b without BTF info, the error is fatal, so let's > > propagate it and exit accordingly. > > Thanks for the patch. > > I'm curious how the kernel will react if we want to load the BPF. > Probably the verifier will reject as it calls some helpers like > bpf_get_current_task_btf(). > > I think it used to work without BTF - the callstack (default) and task > output mode won't need it. It'd be nice if we could run it when the > kernel doesn't have BTF. But maybe it's out of scope of this patch. > > 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 Tycho