From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752919AbaB0WE3 (ORCPT ); Thu, 27 Feb 2014 17:04:29 -0500 Received: from mail-qg0-f41.google.com ([209.85.192.41]:51234 "EHLO mail-qg0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751586AbaB0WE1 (ORCPT ); Thu, 27 Feb 2014 17:04:27 -0500 Date: Thu, 27 Feb 2014 17:06:36 -0500 (EST) From: Vince Weaver To: Vince Weaver cc: Steven Rostedt , "H. Peter Anvin" , Peter Zijlstra , Linux Kernel , Ingo Molnar Subject: Re: perf_fuzzer compiled for x32 causes reboot In-Reply-To: Message-ID: References: <18f0cea3-7e3b-4477-b433-0269f3de976b@email.android.com> <20140224172536.GD9987@twins.programming.kicks-ass.net> <530B841F.5050803@zytor.com>

<530B90A5.3090302@zytor.com> <20140224141329.1cd3bb52@gandalf.local.home> <20140224193043.GP6835@laptop.programming.kicks-ass.net> <530C12CA.6070308@zytor.com>

<20140225094352.73e0e28c@gandalf.local.home>

User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org I spent some more time on this. I managed to get a trace that exhibited the bug practically right away, but still unable to generate a reproducible trace :( So instead I'm adding WARN's and trace_printks to see what I can find out. Here's a summary of what I think is happneing. Please let me know if I'm wildly wrong in analyzing this. Userspace accesses the perf ring-buffer-user-page of an event for the first time (in this trace it's a SW_CPU_CLOCK event). This triggers a page_fault to bring in the page. This triggers a TRACEPOINT event (task/task_newtask) which has PERF_SAMPLE_IP|PERF_SAMPLE_TID|PERF_SAMPLE_TIME|PERF_SAMPLE_CALLCHAIN|PERF_SAMPLE_ID|PERF_SAMPLE_CPU|PERF_SAMPLE_PERIOD|PERF_SAMPLE_STREAM_ID|PERF_SAMPLE_WEIGHT|PERF_SAMPLE_DATA_SRC|PERF_SAMPLE_TRANSACTION; and exclude_callchain_kernel=1, triggering a perf_callchain(). Here is a dump of the stack right after we enter perf_callchain() vince@core2:~$ [ 202.320444] ------------[ cut here ]------------ [ 202.324001] WARNING: CPU: 1 PID: 2873 at kernel/events/callchain.c:168 perf_callchain+0x67/0x211() hermal_sys ehci_pci ehci_hcd sg sd_mod usbcore usb_common [ 202.324001] CPU: 1 PID: 2873 Comm: perf_fuzzer Not tainted 3.14.0-rc3+ #24 [ 202.324001] Hardware name: AOpen DE7000/nMCP7ALPx-DE R1.06 Oct.19.2012, BIOS 080015 10/19/2012 [ 202.324001] 00000000000000a8 ffff880119ec1b48 ffffffff81531dc1 00000000000000a8 [ 202.324001] 0000000000000000 ffff880119ec1b88 ffffffff81040ce4 ffff880119ec1b88 [ 202.324001] ffffffff810d416f ffff880119ec1e38 ffff8800cba67800 0000000000000000 [ 202.324001] Call Trace: [ 202.324001] [] dump_stack+0x49/0x60 [ 202.324001] [] warn_slowpath_common+0x81/0x9b [ 202.324001] [] ? perf_callchain+0x67/0x211 [ 202.324001] [] warn_slowpath_null+0x1a/0x1c [ 202.324001] [] perf_callchain+0x67/0x211 [ 202.324001] [] ? local_clock+0x1b/0x24 [ 202.324001] [] perf_prepare_sample+0x7b/0x304 [ 202.324001] [] __perf_event_overflow+0x156/0x1c1 [ 202.324001] [] ? free_pgtables+0xa7/0xc9 [ 202.324001] [] perf_swevent_overflow+0x41/0x5b [ 202.324001] [] perf_swevent_event+0x72/0x74 [ 202.324001] [] perf_tp_event+0xea/0x1ef [ 202.324001] [] ? perf_trace_x86_exceptions+0x4c/0xba [ 202.324001] [] perf_trace_x86_exceptions+0xa8/0xba [ 202.324001] [] ? perf_trace_x86_exceptions+0x4c/0xba [ 202.324001] [] trace_do_page_fault+0x48/0x99 [ 202.324001] [] trace_page_fault+0x22/0x30 [ 202.324001] ---[ end trace 31ccd31b4e82cb42 ]--- This triggers a kernel pagefault because the BP register is not valid and copy_from_user_nmi() tries to copy the user stack area from there. This *should* be OK? And it maybe looks like it works, but then copy_user_handle_tail() causes another page fault again at the invaid BP register. But then the code continues to perf_output_begin() 237.265689: page_fault_kernel: address=0x17a0 ip=copy_user_handle_tail error_code=0x0 237.265689: function: __do_page_fault 237.265689: function: bad_area_nosemaphore 237.265690: function: __bad_area_nosemaphore 237.265690: function: no_context 237.265690: function: fixup_exception 237.265690: function: search_exception_tables 237.265690: function: search_extable 237.265691: function: perf_output_begin 237.265692: bprint: perf_output_begin: VMW: event type 2 config 2a st: 2c3e7 how are we back in __do_page_fault again here? 237.265692: function: __do_page_fault 237.265692: function: down_read_trylock 237.265692: function: _cond_resched 237.265693: function: find_vma 237.265693: function: bad_area 237.265693: function: up_read 237.265693: function: __bad_area_nosemaphore 237.265694: function: is_prefetch 237.265694: function: convert_ip_to_linear 237.265695: function: unhandled_signal 237.265695: function: __printk_ratelimit 237.265695: function: _raw_spin_trylock 237.265695: function: _raw_spin_unlock_irqrestore 237.265696: function: printk 237.265696: function: vprintk_emit [ 202.877004] perf_fuzzer[2873]: segfault at 17a0 ip 00000000004017fd sp 00000000ffd19d10 error 6 in perf_fuzzer[400000+d1000] Vince