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=-0.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no 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 A9B38C432C3 for ; Thu, 14 Nov 2019 15:30:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7DCAE206DC for ; Thu, 14 Nov 2019 15:30:05 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=efficios.com header.i=@efficios.com header.b="JaYWa6uE" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727022AbfKNPaE (ORCPT ); Thu, 14 Nov 2019 10:30:04 -0500 Received: from mail.efficios.com ([167.114.142.138]:49130 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726474AbfKNPaE (ORCPT ); Thu, 14 Nov 2019 10:30:04 -0500 Received: from localhost (ip6-localhost [IPv6:::1]) by mail.efficios.com (Postfix) with ESMTP id C943D41EF34; Thu, 14 Nov 2019 10:30:02 -0500 (EST) Received: from mail.efficios.com ([IPv6:::1]) by localhost (mail02.efficios.com [IPv6:::1]) (amavisd-new, port 10032) with ESMTP id GafNEX8iSwe2; Thu, 14 Nov 2019 10:30:02 -0500 (EST) Received: from localhost (ip6-localhost [IPv6:::1]) by mail.efficios.com (Postfix) with ESMTP id 5B3FE41EF31; Thu, 14 Nov 2019 10:30:02 -0500 (EST) DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com 5B3FE41EF31 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1573745402; bh=AvTeKCGgoP6UwyZIW9re0q4KBrw1MiiN762zJDFBeTU=; h=Date:From:To:Message-ID:MIME-Version; b=JaYWa6uEpB0327zzAEc6404aorwZPriCxMgwlmRqGEWF7odx8u50yV04rskGvoIkJ vjmRcBIs5rVRzcrjkNUexRb3QnQ6LsRUppA2s39FEqZ9stHY2R/kBtr5r88QeZ9peR GpyYyS7gqqhirwFJrz0AF8S4KFCegMsZ+IyxlJSdw+xNeDSOwhOd80NYSA84RXe+X1 r0dyfD5ojuwKegojbb1lXpx5RykDRInzeJVMwBTVwoZLvO5Hyk830sWoH5Ivv3eMp3 qfF/okqt99Rdx69pu+6EerewQuTtBJjpbYXf8Ne+2L6ApZzwFAhvZ36Cr3tgKWMG3k Bjo76esD91JYQ== X-Virus-Scanned: amavisd-new at efficios.com Received: from mail.efficios.com ([IPv6:::1]) by localhost (mail02.efficios.com [IPv6:::1]) (amavisd-new, port 10026) with ESMTP id BOWoKGWznvZg; Thu, 14 Nov 2019 10:30:02 -0500 (EST) Received: from mail02.efficios.com (mail02.efficios.com [167.114.142.138]) by mail.efficios.com (Postfix) with ESMTP id F1F0D41EF23; Thu, 14 Nov 2019 10:30:01 -0500 (EST) Date: Thu, 14 Nov 2019 10:30:01 -0500 (EST) From: Mathieu Desnoyers To: Peter Zijlstra Cc: paulmck , x86 , linux-kernel , rostedt , Masami Hiramatsu , bristot , jbaron , Linus Torvalds , Thomas Gleixner , Ingo Molnar , Nadav Amit , "H. Peter Anvin" , Andy Lutomirski , Ard Biesheuvel , Josh Poimboeuf , Jessica Yu , Alexei Starovoitov Message-ID: <1849439575.148.1573745401685.JavaMail.zimbra@efficios.com> In-Reply-To: <20191114152829.GA4131@hirez.programming.kicks-ass.net> References: <20191111131252.921588318@infradead.org> <20191111132458.162172862@infradead.org> <394483573.90.1573659752560.JavaMail.zimbra@efficios.com> <20191114135311.GW4131@hirez.programming.kicks-ass.net> <1135959694.112.1573743977897.JavaMail.zimbra@efficios.com> <20191114151323.GK2865@paulmck-ThinkPad-P72> <135240750.136.1573744944568.JavaMail.zimbra@efficios.com> <20191114152829.GA4131@hirez.programming.kicks-ass.net> Subject: Re: [PATCH -v5 12/17] x86/kprobes: Fix ordering MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [167.114.142.138] X-Mailer: Zimbra 8.8.15_GA_3888 (ZimbraWebClient - FF70 (Linux)/8.8.15_GA_3869) Thread-Topic: x86/kprobes: Fix ordering Thread-Index: 8sJONkpl+FM/HNDAhoITrgY+ypVVLQ== Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ----- On Nov 14, 2019, at 10:28 AM, Peter Zijlstra peterz@infradead.org wrote: > On Thu, Nov 14, 2019 at 10:22:24AM -0500, Mathieu Desnoyers wrote: > >> >> > So what we do, after enabling the regular kprobe, is call >> >> > synchronize_rcu_tasks() to wait for each task to have passed through >> >> > schedule(). That guarantees no task is preempted inside the kprobe >> >> > shadow (when it triggers it ensures it resumes execution at an >> >> > instruction boundary further than 5 bytes away). >> >> >> >> Indeed, given that synchronize_rcu_tasks() awaits for voluntary context >> >> switches (or user-space execution), it guarantees that no task was preempted >> >> within the kprobe shadow. >> >> >> >> Considering that synchronize_rcu_tasks() is meant only for code rewriting, >> >> I wonder if it would make sense to include the core serializing guarantees >> >> within this RCU API ? >> > >> > As in have synchronize_rcu_tasks() do the IPI-sync love before doing >> > the current wait-for-voluntary-context-switch work? >> >> This is what I have in mind, yes, based on the assumption that the only >> intended use-case for synchronize_rcu_tasks() is code patching. > > I don't think that is needed. As per the patch under discussion, we > unconditionally need that IPI-sync (even for !optimized) but we only > need the synchonize_rcu_tasks() thing for optimized kprobes. > > Also, they really do two different things. Lets not tie them together. I'm fine with this approach, I just thought it would be good to consider the alternative. Thanks! Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com