From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763836AbdDSNpF (ORCPT ); Wed, 19 Apr 2017 09:45:05 -0400 Received: from mx1.redhat.com ([209.132.183.28]:52704 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1763799AbdDSNpC (ORCPT ); Wed, 19 Apr 2017 09:45:02 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com A657A81138 Authentication-Results: ext-mx03.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx03.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=jpoimboe@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com A657A81138 Date: Wed, 19 Apr 2017 08:44:57 -0500 From: Josh Poimboeuf To: Steven Rostedt Cc: LKML , Ingo Molnar , Thomas Gleixner , Andy Lutomirski , "H. Peter Anvin" Subject: Re: WARNING: kernel stack frame pointer has bad value Message-ID: <20170419134457.l7gdyuf4xbe4nns5@treble> References: <20170418233714.14fbf55d@grimm.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20170418233714.14fbf55d@grimm.local.home> User-Agent: Mutt/1.6.0.1 (2016-04-01) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Wed, 19 Apr 2017 13:45:02 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 18, 2017 at 11:37:14PM -0400, Steven Rostedt wrote: > Josh, > > I'm starting to get a bunch of these warnings, and I'm thinking they > are false positives. The stack frame error is recorded at a call from > entry_SYSCALL_64_fastpath, where I would expect the bp to not be valid. > > To trigger this, I only need to go into /sys/kernel/debug/tracing and > echo function > current_tracer then cat trace. Maybe function tracer > stack frames is messing it up some how, but it always fails at the > entry call. > > Here's the dump; > > WARNING: kernel stack frame pointer at ffff8800bda0ff30 in sshd:1090 has bad value 000055b32abf1fa8 ... > ffff8800bda0ff20: ffff8800bda0ff30 (0xffff8800bda0ff30) > ffff8800bda0ff28: ffffffff810dc945 (SyS_rt_sigprocmask+0x5/0x1a0) > ffff8800bda0ff30: 000055b32abf1fa8 (0x55b32abf1fa8) > ffff8800bda0ff38: ffffffff81cf502a (entry_SYSCALL_64_fastpath+0x18/0xad) > ffff8800bda0ff40: 000055b32abf1fa8 (0x55b32abf1fa8) > ffff8800bda0ff48: ffffffff810dc945 (SyS_rt_sigprocmask+0x5/0x1a0) > ffff8800bda0ff50: ffffffff81cf502a (entry_SYSCALL_64_fastpath+0x18/0xad) Thanks for reporting, I hadn't seen this one yet. The problem is that the unwinder expects the last frame pointer to be at a certain address (0xffff8800bda0ff48 in this case), so it can know that it reached the end. It's confused by the save_mcount_regs macro, which builds some fake frames -- which is good -- but then the last frame is at a different offset than what the unwinder expects. Would it be possible for ftrace to rewrite the stack so that it looks like this instead? > ffff8800bda0ff38: ffff8800bda0ff48 (0xffff8800bda0ff48) > ffff8800bda0ff40: ffffffff810dc945 (SyS_rt_sigprocmask+0x5/0x1a0) > ffff8800bda0ff48: 000055b32abf1fa8 (0x55b32abf1fa8) > ffff8800bda0ff50: ffffffff81cf502a (entry_SYSCALL_64_fastpath+0x18/0xad) In other words it would overwrite the "SyS_rt_sigprocmask+0x5/0x1a0" value on the stack at ffff8800bda0ff48 with the original bp, instead of appending to the existing stack. If you would be ok with such an approach, I could take a stab at it. The alternative would be to change the unwinder, but I would rather avoid having to detect another special case if possible. -- Josh