From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CF07CC072B5 for ; Fri, 24 May 2019 12:12:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A2A142081C for ; Fri, 24 May 2019 12:12:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391387AbfEXMMY (ORCPT ); Fri, 24 May 2019 08:12:24 -0400 Received: from mail.kernel.org ([198.145.29.99]:48654 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2391253AbfEXMMX (ORCPT ); Fri, 24 May 2019 08:12:23 -0400 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id CD98421773; Fri, 24 May 2019 12:12:21 +0000 (UTC) Date: Fri, 24 May 2019 08:12:19 -0400 From: Steven Rostedt To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Andrew Morton , Thomas Gleixner , Masami Hiramatsu , Josh Poimboeuf , Frederic Weisbecker , Joel Fernandes , Andy Lutomirski , Mark Rutland , Namhyung Kim , "Frank Ch. Eigler" Subject: Re: [RFC][PATCH 03/14 v2] function_graph: Allow multiple users to attach to function graph Message-ID: <20190524081219.25de03f6@gandalf.local.home> In-Reply-To: <20190524112608.GJ2589@hirez.programming.kicks-ass.net> References: <20190520142001.270067280@goodmis.org> <20190520142156.992391836@goodmis.org> <20190524112608.GJ2589@hirez.programming.kicks-ass.net> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; 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 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 24 May 2019 13:26:08 +0200 Peter Zijlstra wrote: > But but but but.. why not add all the required bits to the shadow stack > in the first place and do away with the array entirely? What required bits would that be? The pointer to the fgraph_ops, because we need that to pass to the calling function. > > So on ret, just keep POP'ing until either the stack is empty or the > entry is for another function. When we hit a fgraph_ops, how do we know if it was freed or not? We can't just blindly reference it. The idea of the array, is that we can maintain state in a single location of when the fgraph_ops is freed. If we return from a function, we have an index and a counter, and if the counter doesn't match with what's in the array, then we know that the fgraph_ops is no longer around and we just drop it. The reason for the array, is to keep track of if the fgraph_ops has been freed or not. Otherwise, when we unregister the fgraph_ops, we would need to search all shadow stacks, looking for it to unreference it. Believe me, I rather not have that array, but I couldn't come up with a better solution to handle freeing of fgraph_ops. -- Steve