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=-2.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 E57F7C04EB8 for ; Tue, 4 Dec 2018 07:40:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A4E98214C1 for ; Tue, 4 Dec 2018 07:40:15 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="VCW/J9ji" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A4E98214C1 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726117AbeLDHkO (ORCPT ); Tue, 4 Dec 2018 02:40:14 -0500 Received: from mail.kernel.org ([198.145.29.99]:45638 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726007AbeLDHkO (ORCPT ); Tue, 4 Dec 2018 02:40:14 -0500 Received: from devnote (p35161-mobac01.tokyo.ocn.ne.jp [153.233.26.161]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 57A4320834; Tue, 4 Dec 2018 07:40:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1543909212; bh=TYS4YnpfAikJN3oNMunPEXqdavsXhUXkQFfrtux+tfY=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=VCW/J9jiuNfBx0J6LFO0RUA5XgKtBWgbJIREGlQWIH2n7ox5B3USQyUnFcbmByd/e Lk/B778jLg9E21wJnV9wd58ZmQxMFvATOfJ2JtwaDpzgFev3Y5FnAh+SfCkXCYYzxU ZuGb0DHMojbB5QPeebbeDsh+dAfYsOt83phHVRIo= Date: Tue, 4 Dec 2018 16:40:07 +0900 From: Masami Hiramatsu To: Steven Rostedt Cc: LKML , Ingo Molnar , Thomas Gleixner , Peter Zijlstra , "H. Peter Anvin" , Andy Lutomirski Subject: Re: Strange hang with gcc 8 of kprobe multiple_kprobes test Message-Id: <20181204164007.956a3458c9fd301b3d173eba@kernel.org> In-Reply-To: <20181203211807.17e03384@vmware.local.home> References: <20181203211807.17e03384@vmware.local.home> X-Mailer: Sylpheed 3.5.0 (GTK+ 2.24.30; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Steve, On Mon, 3 Dec 2018 21:18:07 -0500 Steven Rostedt wrote: > Hi Masami, > > I started testing some of my new code and the system got into a > strange state. Debugging further, I found the cause came from the > kprobe tests. It became stranger to me that I could reproduce it with > older kernels. I went back as far as 4.16 and it triggered. I thought > this very strange because I ran this test on all those kernels in the > past. > > After a bit of hair pulling, I figured out what changed. I upgraded to > gcc 8.1 (and I reproduce it with 8.2 as well). I convert back to gcc 7 > and the tests pass without issue. OK, let me see. > The issue that I notice when the system gets into this strange state is > that I can't log into the box. Nor can I reboot. Basically it's > anything to do with systemd just doesn't work (insert your jokes here > now, and then let's move on). > > I was able to narrow down what the exact function was that caused the > issues and it is: update_vsyscall() > > gcc 7 looks like this: > > ffffffff81004bf0 : > ffffffff81004bf0: e8 0b cc 9f 00 callq ffffffff81a01800 <__fentry__> > ffffffff81004bf1: R_X86_64_PC32 __fentry__-0x4 > ffffffff81004bf5: 48 8b 07 mov (%rdi),%rax > ffffffff81004bf8: 8b 15 96 5f 34 01 mov 0x1345f96(%rip),%edx # ffffffff8234ab94 > ffffffff81004bfa: R_X86_64_PC32 vclocks_used-0x4 > ffffffff81004bfe: 83 05 7b 84 6f 01 01 addl $0x1,0x16f847b(%rip) # ffffffff826fd080 > ffffffff81004c00: R_X86_64_PC32 vsyscall_gtod_data-0x5 > ffffffff81004c05: 8b 48 24 mov 0x24(%rax),%ecx > ffffffff81004c08: b8 01 00 00 00 mov $0x1,%eax > ffffffff81004c0d: d3 e0 shl %cl,%eax > > And gcc 8 looks like this: > > ffffffff81004c90 : > ffffffff81004c90: e8 6b cb 9f 00 callq ffffffff81a01800 <__fentry__> > ffffffff81004c91: R_X86_64_PC32 __fentry__-0x4 > ffffffff81004c95: 48 8b 07 mov (%rdi),%rax > ffffffff81004c98: 83 05 e1 93 6f 01 01 addl $0x1,0x16f93e1(%rip) # ffffffff826fe080 Hm this is a RIP relative instruction, it should be modified by kprobes. > ffffffff81004c9a: R_X86_64_PC32 vsyscall_gtod_data-0x5 > ffffffff81004c9f: 8b 50 24 mov 0x24(%rax),%edx > ffffffff81004ca2: 8b 05 ec 5e 34 01 mov 0x1345eec(%rip),%eax # ffffffff8234ab94 > ffffffff81004ca4: R_X86_64_PC32 vclocks_used-0x4 > > The test adds a kprobe (optimized) at udpate_vsyscall+5. And will > insert a jump on the two instructions after fentry. The difference > between v7 and v8 is that v7 is touching vclocks_used and v8 is > touching vsyscall_gtod_data. > > Is there some black magic going on with the vsyscall area with > vsyscall_gtod_data that is causing havoc when a kprobe is added there? I think it might miss something when preprocessing RIP relative instruction. Could you disable jump optimization as below and test what happen on update_vsyscall+5 AND update_vsyscall+8? (RIP relative preprocess must happen even if the jump optimization is disabled) # echo 0 > /proc/sys/debug/kprobes-optimization > I can dig a little more into this, but I'm currently at my HQ office > with a lot of other objectives that I must get done, and I can't work > on this much more this week. OK, let me try to reproduce it in my environment. > > I included my config (for my virt machine, which I was also able to > trigger it with). Thanks, but I think it should not depend on the kconfig. > > The test that triggers this bug is: > > tools/testing/selftests/ftrace/test.d/kprobe/multiple_kprobes.tc > > It runs the test fine, but other things just start to act up after I > run it. Yeah, thank you for digging it down. It is now much easier to me. > > I notice that when I get into the state, journald and the dbus_daemon > are constantly running. Perhaps the userspace time keeping went bad? Yeah, I think so. Maybe addl instruction becomes broken. Thank you, -- Masami Hiramatsu