From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756269AbcHBVQ0 (ORCPT ); Tue, 2 Aug 2016 17:16:26 -0400 Received: from smtprelay0030.hostedemail.com ([216.40.44.30]:56515 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753236AbcHBVQR (ORCPT ); Tue, 2 Aug 2016 17:16:17 -0400 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Spam-Summary: 2,0,0,,d41d8cd98f00b204,rostedt@goodmis.org,:::::::::::::::::::::::::,RULES_HIT:41:355:379:541:599:800:960:973:988:989:1260:1277:1311:1313:1314:1345:1359:1437:1515:1516:1518:1534:1541:1593:1594:1711:1730:1747:1777:1792:2393:2553:2559:2562:3138:3139:3140:3141:3142:3353:3622:3865:3866:3867:3868:3871:3872:3874:4605:5007:6117:6261:6742:7875:7903:10004:10400:10848:10967:11026:11232:11473:11658:11914:12043:12296:12438:12517:12519:12555:12740:13069:13138:13161:13229:13231:13255:13311:13357:13439:14181:14659:14721:21080:21433,0,RBL:none,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0,MSF:not bulk,SPF:fn,MSBL:0,DNSBL:none,Custom_rules:0:0:0,LFtime:5,LUA_SUMMARY:none X-HE-Tag: doll31_5363d17979658 X-Filterd-Recvd-Size: 3105 Date: Tue, 2 Aug 2016 17:16:10 -0400 From: Steven Rostedt To: Josh Poimboeuf Cc: Thomas Gleixner , Ingo Molnar , "H . Peter Anvin" , x86@kernel.org, linux-kernel@vger.kernel.org, Andy Lutomirski , Linus Torvalds , Brian Gerst , Kees Cook , Peter Zijlstra , Frederic Weisbecker , Byungchul Park Subject: Re: [PATCH 05/19] x86/dumpstack: fix function graph tracing stack dump reliability issues Message-ID: <20160802171610.09156c90@gandalf.local.home> In-Reply-To: <20160802210011.k6li4mnyvky5jtev@treble> References: <20160729185521.62a5cd2a@gandalf.local.home> <20160730005059.5krpl2xsvqfbnntj@treble> <20160729222036.340b51ce@grimm.local.home> <20160730135125.qqw5qz24szlc2crz@treble> <20160801102821.1d6261a9@gandalf.local.home> <20160801153633.c7sa2rclkqwbdagd@treble> <20160802210011.k6li4mnyvky5jtev@treble> X-Mailer: Claws Mail 3.13.2 (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 List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2 Aug 2016 16:00:11 -0500 Josh Poimboeuf wrote: [] nmi_raise_cpu_backtrace+0x1b/0x20 > > The ret_stack is out of sync with the stack dump because the stack dump > was started with the regs from the NMI, instead of being started from > the current frame. > > So I guess there are a couple of ways to fix it: > > a) keep track of the return address pointer like we discussed above; > > or > > b) have the unwinder count the # of skipped frames which refer to > 'return_to_handler', and pass that as the initial index value to > ftrace_graph_ret_addr(). > > Option a) would be much cleaner. But to fix it for both mcount and > fentry, we couldn't override 'fp' so I guess we'd need to add a new > field to ftrace_ret_stack. Actually, what about calling ftrace_graph_ret_addr() to figure out the next stack conversion only if reliable or CONFIG_FRAME_POINTER is not enabled? unsigned long real_addr = addr; [...] if (!IS_ENABLED(CONFIG_FRAME_POINTER) || reliable) real_addr = ftrace_graph_ret_addr(task, graph, addr); if (addr != real_addr) ops->address(data, addr, 0); ops->address(data, real_addr, reliable); Then we only need the fp use case when FRAME_POINTER is not set. As mcount forces FRAME_POINTER, we only need to worry about the fentry case. -- Steve > > Option b) is uglier, but I could probably make it work with the new > unwinder. >