From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751977AbcBYVcb (ORCPT ); Thu, 25 Feb 2016 16:32:31 -0500 Received: from mail-wm0-f41.google.com ([74.125.82.41]:37389 "EHLO mail-wm0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751734AbcBYVca (ORCPT ); Thu, 25 Feb 2016 16:32:30 -0500 Subject: Re: BUG: unable to handle kernel paging request from pty_write [was: Linux 4.4.2] To: Linus Torvalds , Peter Hurley References: <20160217203730.GA14820@kroah.com> <56CED373.9060603@suse.cz> <56CF4A83.3040408@hurleysoftware.com> <56CF64C9.8050705@hurleysoftware.com> Cc: Greg KH , Linux Kernel Mailing List , Andrew Morton , stable , lwn@lwn.net, Steven Rostedt From: Jiri Slaby X-Enigmail-Draft-Status: N1110 Message-ID: <56CF72EA.9040009@suse.cz> Date: Thu, 25 Feb 2016 22:32:26 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/25/2016, 09:51 PM, Linus Torvalds wrote: > Jiri, can you check your try_to_wake_up() disassembly for some > indirect "jmp" instructions? Nope, there is none. I will reply to all your questions tomorrow. Just quickly, as I have to go (and don't want you to duplicate efforts) the kernel which was used can be obtained here: https://build.opensuse.org/package/binaries/openSUSE:Factory:Staging:I/kernel-default?repository=standard The issue is very weird, indeed, this is what I noted to our bugzilla: The stack trace ends in call of try_to_wake_up. Then, there it has to be some of the indirect calls: callq *0x40(%rax) p->sched_class->select_task_rq from select_task_rq RAX is 0x00000000bb37e180, barely can be read with offset 0x40 callq *0xd85656(%rip) # ffffffff81e2aba0 smp_ops.smp_send_reschedule from ttwu_queue_remote Which hardly can be it, given smp_ops is static. So it has to be some other "call *" from a nested function :(. Interestingly, RBP contains address inside try_to_wake_up -- ffffffff810a535a (dunno why) which is: ffffffff810a5355: e8 66 a0 ff ff callq ffffffff8109f3c0 ffffffff810a535a: e9 9d fe ff ff jmpq ffffffff810a51fc ttwu_stat does in the begginning: mov $0x16e80,%r14 which is what we actually still have in r14 when it crashes. The first ttwu_stat's "if" has to go through the true branch (otherwise r14 would be overwritten). Another note: we die when jmp/calling to 0xffff88023fd40000. RSI=RDI=0xffff88023fdd6e80. RSI-RIP is 0x96e80, which is R14 + 0x80000. Coincidence? thanks, -- js suse labs