From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1163981AbdAIRgv (ORCPT ); Mon, 9 Jan 2017 12:36:51 -0500 Received: from mx1.redhat.com ([209.132.183.28]:38980 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S967583AbdAIRgu (ORCPT ); Mon, 9 Jan 2017 12:36:50 -0500 Date: Mon, 9 Jan 2017 11:36:48 -0600 From: Josh Poimboeuf To: Masami Hiramatsu Cc: Ingo Molnar , linux-kernel@vger.kernel.org, Peter Zijlstra , Ananth N Mavinakayanahalli , Thomas Gleixner , "H . Peter Anvin" , Andrey Konovalov , Andy Lutomirski Subject: Re: [PATCH tip/master v4] kprobes: extable: Identify kprobes' insn-slots as kernel text area Message-ID: <20170109173648.k7dxu7nz22qc6upq@treble> References: <20170104100102.GE25813@worktop.programming.kicks-ass.net> <148388747896.6869.6354262871751682264.stgit@devbox> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <148388747896.6869.6354262871751682264.stgit@devbox> 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 [10.5.110.30]); Mon, 09 Jan 2017 17:36:51 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Jan 08, 2017 at 11:58:09PM +0900, Masami Hiramatsu wrote: > Make __kernel_text_address()/kernel_text_address() returns > true if the given address is on a kprobe's instruction slot, > which is generated by kprobes as a trampoline code. > This can help stacktraces to determine the address is on a > text area or not. > > To implement this without any sleep in is_kprobe_*_slot(), > this also modify insn_cache page list as a rcu list. It may > increase processing deley (not processing time) for garbage > slot collection, because it requires to wait an additional > rcu grance period when freeing a page from the list. > However, since it is not a hot path, we may not take care of it. > > Note: this can give a small overhead to stack unwinders because > this adds 2 checks in __kernel_text_address(). However, the > impact should be very small, kprobe_insn_pages list has 1 entry > per 256 probes(on x86, on arm/arm64 it will be 1024 probes), > and kprobe_optinsn_pages has 1 entry per 32 probes(on x86). > In most use cases, the number of kprobe events may be less > than 20, this means is_kprobe_*_slot() will check just 1 entry. > > Signed-off-by: Masami Hiramatsu Thanks for doing this Masami! I verified that it works: Tested-by: Josh Poimboeuf I suspect that BPF generated code also has the same issue, so I'll leave the unwinder warning disabled for now. BTW, I think we'll have more problems with generated code if/when we move to an x86 DWARF unwinder, because it won't have any idea how to unwind past generated code. Long term I wonder if it would make sense to create some kind of framework for creating or registering generated code, so we can solve these types of problems in a single place. -- Josh