From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3vNhmP6jdmzDq5x for ; Thu, 16 Feb 2017 01:40:53 +1100 (AEDT) Date: Wed, 15 Feb 2017 08:40:44 -0600 From: Josh Poimboeuf To: Miroslav Benes Cc: Jessica Yu , Jiri Kosina , Petr Mladek , linux-kernel@vger.kernel.org, live-patching@vger.kernel.org, Michael Ellerman , Heiko Carstens , x86@kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, Vojtech Pavlik , Jiri Slaby , Chris J Arges , Andy Lutomirski , Ingo Molnar , Peter Zijlstra , Kamalesh Babulal , Balbir Singh Subject: Re: [PATCH v5 01/15] stacktrace/x86: add function for detecting reliable stack traces Message-ID: <20170215144044.yn63piijka7zqqlz@treble> References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 In-Reply-To: List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wed, Feb 15, 2017 at 01:18:40PM +0100, Miroslav Benes wrote: > On Mon, 13 Feb 2017, Josh Poimboeuf wrote: > > > For live patching and possibly other use cases, a stack trace is only > > useful if it can be assured that it's completely reliable. Add a new > > save_stack_trace_tsk_reliable() function to achieve that. > > > > Note that if the target task isn't the current task, and the target task > > is allowed to run, then it could be writing the stack while the unwinder > > is reading it, resulting in possible corruption. So the caller of > > save_stack_trace_tsk_reliable() must ensure that the task is either > > 'current' or inactive. > > > > save_stack_trace_tsk_reliable() relies on the x86 unwinder's detection > > of pt_regs on the stack. If the pt_regs are not user-mode registers > > from a syscall, then they indicate an in-kernel interrupt or exception > > (e.g. preemption or a page fault), in which case the stack is considered > > unreliable due to the nature of frame pointers. > > > > It also relies on the x86 unwinder's detection of other issues, such as: > > > > - corrupted stack data > > - stack grows the wrong way > > - stack walk doesn't reach the bottom > > - user didn't provide a large enough entries array > > > > Such issues are reported by checking unwind_error() and !unwind_done(). > > > > Also add CONFIG_HAVE_RELIABLE_STACKTRACE so arch-independent code can > > determine at build time whether the function is implemented. > > > > Signed-off-by: Josh Poimboeuf > > I do not see any difference from 4.1 version, so my > > Reviewed-by: Miroslav Benes Sorry, forgot to add your Reviewed-by from last time. The patch is indeed the same. Thanks! -- Josh