From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_NEOMUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C78EDC282CE for ; Wed, 22 May 2019 18:07:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A549720863 for ; Wed, 22 May 2019 18:07:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729362AbfEVSHx (ORCPT ); Wed, 22 May 2019 14:07:53 -0400 Received: from mx1.redhat.com ([209.132.183.28]:45108 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727975AbfEVSHw (ORCPT ); Wed, 22 May 2019 14:07:52 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id D2DC98830F; Wed, 22 May 2019 18:07:51 +0000 (UTC) Received: from treble (ovpn-120-127.rdu2.redhat.com [10.10.120.127]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2D63262660; Wed, 22 May 2019 18:07:51 +0000 (UTC) Date: Wed, 22 May 2019 13:07:49 -0500 From: Josh Poimboeuf To: Kairui Song Cc: Peter Zijlstra , Song Liu , lkml , Kernel Team Subject: Re: Getting empty callchain from perf_callchain_kernel() Message-ID: <20190522180749.qpwdlhkcitxiazco@treble> References: <3CD3EE63-0CD2-404A-A403-E11DCF2DF8D9@fb.com> <20190517074600.GJ2623@hirez.programming.kicks-ass.net> <20190517081057.GQ2650@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20180716 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Wed, 22 May 2019 18:07:51 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, May 17, 2019 at 04:15:39PM +0800, Kairui Song wrote: > On Fri, May 17, 2019 at 4:11 PM Peter Zijlstra wrote: > > > > On Fri, May 17, 2019 at 09:46:00AM +0200, Peter Zijlstra wrote: > > > On Thu, May 16, 2019 at 11:51:55PM +0000, Song Liu wrote: > > > > Hi, > > > > > > > > We found a failure with selftests/bpf/tests_prog in test_stacktrace_map (on bpf/master > > > > branch). > > > > > > > > After digging into the code, we found that perf_callchain_kernel() is giving empty > > > > callchain for tracepoint sched/sched_switch. And it seems related to commit > > > > > > > > d15d356887e770c5f2dcf963b52c7cb510c9e42d > > > > ("perf/x86: Make perf callchains work without CONFIG_FRAME_POINTER") > > > > > > > > Before this commit, perf_callchain_kernel() returns callchain with regs->ip. With > > > > this commit, regs->ip is not sent for !perf_hw_regs(regs) case. > > > > > > So while I think the below is indeed right; we should store regs->ip > > > regardless of the unwind path chosen, I still think there's something > > > fishy if this results in just the 1 entry. > > > > > > The sched/sched_switch event really should have a non-trivial stack. > > > > > > Let me see if I can reproduce with just perf. > > > > $ perf record -g -e "sched:sched_switch" -- make clean > > $ perf report -D > > > > 12 904071759467 0x1790 [0xd0]: PERF_RECORD_SAMPLE(IP, 0x1): 7236/7236: 0xffffffff81c29562 period: 1 addr: 0 > > ... FP chain: nr:10 > > ..... 0: ffffffffffffff80 > > ..... 1: ffffffff81c29562 > > ..... 2: ffffffff81c29933 > > ..... 3: ffffffff8111f688 > > ..... 4: ffffffff81120b9d > > ..... 5: ffffffff81120ce5 > > ..... 6: ffffffff8100254a > > ..... 7: ffffffff81e0007d > > ..... 8: fffffffffffffe00 > > ..... 9: 00007f9b6cd9682a > > ... thread: sh:7236 > > ...... dso: /lib/modules/5.1.0-12177-g41bbb9129767/build/vmlinux > > > > > > IOW, it seems to 'work'. > > > > Hi, I think the actual problem is that bpf_get_stackid_tp (and maybe > some other bfp functions) is now broken, or, strating an unwind > directly inside a bpf program will end up strangely. It have following > kernel message: > > WARNING: kernel stack frame pointer at 0000000070cad07c in > test_progs:1242 has bad value 00000000ffd4497e > > And in the debug message: > > [ 160.460287] 000000006e117175: ffffffffaa23a0e8 > (get_perf_callchain+0x148/0x280) > [ 160.460287] 0000000002e8715f: 0000000000c6bba0 (0xc6bba0) > [ 160.460288] 00000000b3d07758: ffff9ce3f9790000 (0xffff9ce3f9790000) > [ 160.460289] 0000000055c97836: ffff9ce3f9790000 (0xffff9ce3f9790000) > [ 160.460289] 000000007cbb140a: 000000010000007f (0x10000007f) > [ 160.460290] 000000007dc62ac9: 0000000000000000 ... > [ 160.460290] 000000006b41e346: 1c7da01cd70c4000 (0x1c7da01cd70c4000) > [ 160.460291] 00000000f23d1826: ffffd89cffc3ae80 (0xffffd89cffc3ae80) > [ 160.460292] 00000000f9a16017: 000000000000007f (0x7f) > [ 160.460292] 00000000a8e62d44: 0000000000000000 ... > [ 160.460293] 00000000cbc83c97: ffffb89d00d8d000 (0xffffb89d00d8d000) > [ 160.460293] 0000000092842522: 000000000000007f (0x7f) > [ 160.460294] 00000000dafbec89: ffffb89d00c6bc50 (0xffffb89d00c6bc50) > [ 160.460296] 000000000777e4cf: ffffffffaa225d97 (bpf_get_stackid+0x77/0x470) > [ 160.460296] 000000009942ea16: 0000000000000000 ... > [ 160.460297] 00000000a08006b1: 0000000000000001 (0x1) > [ 160.460298] 000000009f03b438: ffffb89d00c6bc30 (0xffffb89d00c6bc30) > [ 160.460299] 000000006caf8b32: ffffffffaa074fe8 (__do_page_fault+0x58/0x90) > [ 160.460300] 000000003a13d702: 0000000000000000 ... > [ 160.460300] 00000000e2e2496d: ffff9ce300000000 (0xffff9ce300000000) > [ 160.460301] 000000008ee6b7c2: ffffd89cffc3ae80 (0xffffd89cffc3ae80) > [ 160.460301] 00000000a8cf6d55: 0000000000000000 ... > [ 160.460302] 0000000059078076: ffffd89cffc3ae80 (0xffffd89cffc3ae80) > [ 160.460303] 00000000c6aac739: ffff9ce3f1e18eb0 (0xffff9ce3f1e18eb0) > [ 160.460303] 00000000a39aff92: ffffb89d00c6bc60 (0xffffb89d00c6bc60) > [ 160.460305] 0000000097498bf2: ffffffffaa1f4791 (bpf_get_stackid_tp+0x11/0x20) > [ 160.460306] 000000006992de1e: ffffb89d00c6bc78 (0xffffb89d00c6bc78) > [ 160.460307] 00000000dacd0ce5: ffffffffc0405676 (0xffffffffc0405676) > [ 160.460307] 00000000a81f2714: 0000000000000000 ... > > # Note here is the invalid frame pointer > [ 160.460308] 0000000070cad07c: ffffb89d00a1d000 (0xffffb89d00a1d000) > [ 160.460308] 00000000f8f194e4: 0000000000000001 (0x1) > [ 160.460309] 000000002134f42a: ffffd89cffc3ae80 (0xffffd89cffc3ae80) > [ 160.460310] 00000000f9345889: ffff9ce3f1e18eb0 (0xffff9ce3f1e18eb0) > [ 160.460310] 000000008ad22a42: 0000000000000000 ... > [ 160.460311] 0000000073808173: ffffb89d00c6bce0 (0xffffb89d00c6bce0) > [ 160.460312] 00000000c9effff4: ffffffffaa1f48d1 (trace_call_bpf+0x81/0x100) > [ 160.460313] 00000000c5d8ebd1: ffffb89d00c6bcc0 (0xffffb89d00c6bcc0) > [ 160.460315] 00000000bce0b072: ffffffffab651be0 > (event_sched_migrate_task+0xa0/0xa0) > [ 160.460316] 00000000355cf319: 0000000000000000 ... > [ 160.460316] 000000003b67f2ad: ffffd89cffc3ae80 (0xffffd89cffc3ae80) > [ 160.460316] 000000009a77e20b: ffff9ce3fba25000 (0xffff9ce3fba25000) > [ 160.460317] 0000000032cf7376: 0000000000000001 (0x1) > [ 160.460317] 000000000051db74: ffffb89d00c6bd20 (0xffffb89d00c6bd20) > [ 160.460318] 0000000040eb3bf7: ffffffffaa22be81 > (perf_trace_run_bpf_submit+0x41/0xb0) Is there an easy way to recreate this? -- Josh