From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mathieu Desnoyers Subject: Re: [RFC PATCH for 4.17 02/21] rseq: Introduce restartable sequences system call (v12) Date: Wed, 28 Mar 2018 10:47:54 -0400 (EDT) Message-ID: <1523662633.2105.1522248474778.JavaMail.zimbra@efficios.com> References: <20180327160542.28457-1-mathieu.desnoyers@efficios.com> <20180327160542.28457-3-mathieu.desnoyers@efficios.com> <20180328125004.GV4043@hirez.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20180328125004.GV4043@hirez.programming.kicks-ass.net> Sender: linux-kernel-owner@vger.kernel.org To: Peter Zijlstra Cc: "Paul E. McKenney" , Boqun Feng , Andy Lutomirski , Dave Watson , linux-kernel , linux-api , Paul Turner , Andrew Morton , Russell King , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Andrew Hunter , Andi Kleen , Chris Lameter , Ben Maurer , rostedt , Josh Triplett , Linus Torvalds , Catalin Marinas , Will Deacon List-Id: linux-api@vger.kernel.org ----- On Mar 28, 2018, at 8:50 AM, Peter Zijlstra peterz@infradead.org wrote: > On Tue, Mar 27, 2018 at 12:05:23PM -0400, Mathieu Desnoyers wrote: >> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h >> index fb5fc458547f..66b070444a7e 100644 >> --- a/kernel/sched/sched.h >> +++ b/kernel/sched/sched.h >> @@ -1249,6 +1249,7 @@ static inline void __set_task_cpu(struct task_struct *p, >> unsigned int cpu) >> #endif >> p->wake_cpu = cpu; >> #endif >> + rseq_migrate(p); >> } > > I think you want that in set_task_cpu(), right next to nr_migrations++. This would miss the __set_task_cpu() call from sched_fork() and wake_up_new_task(). Those cases are not accounted as explicit "migrations", but it does change the CPU of the current task. So if for some weird reason userspace wants to fork() while in a rseq critical section, we want to trigger a rseq restart. Note that rseq_fork() implies rseq_preempt(), but userspace can request to track only migrations for a given rseq critical section (by using the RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT flag), so the rseq_preempt() in rseq_fork() is not enough to restart if a migration between CPUs is done across a fork. An alternative to this would be to call rseq_migrate() in rseq_fork(). Thoughts ? Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Cyrus-Session-Id: sloti22d1t05-2532849-1522248503-2-12658632116128713161 X-Sieve: CMU Sieve 3.0 X-Spam-known-sender: no X-Spam-score: 0.0 X-Spam-hits: BAYES_00 -1.9, HEADER_FROM_DIFFERENT_DOMAINS 0.249, ME_NOAUTH 0.01, RCVD_IN_DNSWL_HI -5, T_RP_MATCHES_RCVD -0.01, LANGUAGES en, BAYES_USED global, SA_VERSION 3.4.0 X-Spam-source: IP='209.132.180.67', Host='vger.kernel.org', Country='CN', FromHeader='com', MailFrom='org', XOriginatingCountry='CA' X-Spam-charsets: plain='utf-8' X-Resolved-to: greg@kroah.com X-Delivered-to: greg@kroah.com X-Mail-from: linux-api-owner@vger.kernel.org ARC-Seal: i=1; a=rsa-sha256; cv=none; d=messagingengine.com; s=arctest; t=1522248502; b=GNec3JMd27zL02mp71bO5ZiEOqx7Jo7/KvfgFc7SxqUP5fr NfQDZ6csQaJFxbrOUvzVRbrn3Wu2wkTBN4us/TFviUM0gycjymEUnEnLuqR9TqfU FIBJ39Gr/w2ahCFE+S4B03JPFhQgVJpmBsDdRuRo5bN+WTDR8uVF7J/Ibbelv5Zx IIkB2FctZ1WfdkixetdwrgTp7zts3c3oMSRECJLSyVgf+9N61AT1W5FevUZz/hJx YgHXx9Iwa7YF0Api6DRwAUJ1+IT/1aB9hRHeGR+0ZIzc4GcBhSPQcWYinjHLHvmm 3P76FvfxeFJVcRZnLlV3MILGhDL4zYa3HQENkcg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=date:from:to:cc:message-id:in-reply-to :references:subject:mime-version:content-type :content-transfer-encoding:sender:list-id; s=arctest; t= 1522248502; bh=zPy55IiGyDbBxOnLyAmAYHE9A5S7i4+mA09YOLLw8W4=; b=O hK6kxGg4wudo1naoemmGIxDh/gMyhDzYb+1oruB1o7IL2xRQ0UEktdQ/G/ox4rk5 K/VRCLUljV1d9dNX/ThgfuQBFPCxWbap8hInNHKpejOZmjPxdNV3hY/LvEucsU7x lbft+xBLA1J6eud1zQV+bKRV7HDk5QgExXEzTba/B6Y2bcncMaFsyaJnPrMRmFGe NrXnJQk8QnOuQ5BGfpIqD2jrbS6vj388J/k0gNzJG1lZix93+pOJqJMTqN6rbJNX 4mG+7x0tLeAmuHwvP/Cc59fb72rnZGWnfOL6q24EIKfiorzhP60+nDNO3kGCF0Nj wnTNh4cKlvkS4MGIYqejg== ARC-Authentication-Results: i=1; mx4.messagingengine.com; arc=none (no signatures found); dkim=none (no signatures found); dmarc=none (p=none,has-list-id=yes,d=none) header.from=efficios.com; iprev=pass policy.iprev=209.132.180.67 (vger.kernel.org); spf=none smtp.mailfrom=linux-api-owner@vger.kernel.org smtp.helo=vger.kernel.org; x-aligned-from=fail; x-cm=none score=0; x-ptr=pass x-ptr-helo=vger.kernel.org x-ptr-lookup=vger.kernel.org; x-return-mx=pass smtp.domain=vger.kernel.org smtp.result=pass smtp_org.domain=kernel.org smtp_org.result=pass smtp_is_org_domain=no header.domain=efficios.com header.result=pass header_is_org_domain=yes; x-vs=clean score=-100 state=0 Authentication-Results: mx4.messagingengine.com; arc=none (no signatures found); dkim=none (no signatures found); dmarc=none (p=none,has-list-id=yes,d=none) header.from=efficios.com; iprev=pass policy.iprev=209.132.180.67 (vger.kernel.org); spf=none smtp.mailfrom=linux-api-owner@vger.kernel.org smtp.helo=vger.kernel.org; x-aligned-from=fail; x-cm=none score=0; x-ptr=pass x-ptr-helo=vger.kernel.org x-ptr-lookup=vger.kernel.org; x-return-mx=pass smtp.domain=vger.kernel.org smtp.result=pass smtp_org.domain=kernel.org smtp_org.result=pass smtp_is_org_domain=no header.domain=efficios.com header.result=pass header_is_org_domain=yes; x-vs=clean score=-100 state=0 X-ME-VSCategory: clean X-CM-Envelope: MS4wfMoWPNAVrM80tlJgNh6iBF/OaFXQ7e9evuMAFIiTwQTe8W0jsuLc2jmta/cEuTPWX5QLuxQuq4NmhtjFS8oJ3cACZfECzbhIPj1lRh3WMMv4HbiP4ebV fSmfhQ3efbdAavRe6EGB+Wo95VRNvJU2TWaX+T/GANLUbcKkoQwuPD2qYrkff+x6fawe6o8DQ/jk1rxV/z4rNvfZKxDx06UMErhvMhX2eTnP66lh8FhhfzVk X-CM-Analysis: v=2.3 cv=JLoVTfCb c=1 sm=1 tr=0 a=UK1r566ZdBxH71SXbqIOeA==:117 a=UK1r566ZdBxH71SXbqIOeA==:17 a=FKkrIqjQGGEA:10 a=alcw4SYXYecA:10 a=IkcTkHD0fZMA:10 a=v2DPQv5-lfwA:10 a=FqpbrowB-PMA:10 a=JfrnYn6hAAAA:8 a=7d_E57ReAAAA:8 a=VwQbUJbxAAAA:8 a=A3FP38jFBYwwCQduu2EA:9 a=QEXdDO2ut3YA:10 a=x8gzFH9gYPwA:10 a=1CNFftbPRP8L7MoqJWF3:22 a=jhqOcbufqs7Y1TYCrUUU:22 a=AjGcO6oz07-iQ99wixmX:22 X-ME-CMScore: 0 X-ME-CMCategory: none Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753520AbeC1Or7 (ORCPT ); Wed, 28 Mar 2018 10:47:59 -0400 Received: from mail.efficios.com ([167.114.142.138]:38264 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753512AbeC1Or4 (ORCPT ); Wed, 28 Mar 2018 10:47:56 -0400 Date: Wed, 28 Mar 2018 10:47:54 -0400 (EDT) From: Mathieu Desnoyers To: Peter Zijlstra Cc: "Paul E. McKenney" , Boqun Feng , Andy Lutomirski , Dave Watson , linux-kernel , linux-api , Paul Turner , Andrew Morton , Russell King , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Andrew Hunter , Andi Kleen , Chris Lameter , Ben Maurer , rostedt , Josh Triplett , Linus Torvalds , Catalin Marinas , Will Deacon , Michael Kerrisk , Alexander Viro Message-ID: <1523662633.2105.1522248474778.JavaMail.zimbra@efficios.com> In-Reply-To: <20180328125004.GV4043@hirez.programming.kicks-ass.net> References: <20180327160542.28457-1-mathieu.desnoyers@efficios.com> <20180327160542.28457-3-mathieu.desnoyers@efficios.com> <20180328125004.GV4043@hirez.programming.kicks-ass.net> Subject: Re: [RFC PATCH for 4.17 02/21] rseq: Introduce restartable sequences system call (v12) 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 8.8.7_GA_1964 (ZimbraWebClient - FF52 (Linux)/8.8.7_GA_1964) Thread-Topic: rseq: Introduce restartable sequences system call (v12) Thread-Index: g8G18zlpGluv5V0WfpsSPI+DeO7luw== Sender: linux-api-owner@vger.kernel.org X-Mailing-List: linux-api@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: ----- On Mar 28, 2018, at 8:50 AM, Peter Zijlstra peterz@infradead.org wrote: > On Tue, Mar 27, 2018 at 12:05:23PM -0400, Mathieu Desnoyers wrote: >> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h >> index fb5fc458547f..66b070444a7e 100644 >> --- a/kernel/sched/sched.h >> +++ b/kernel/sched/sched.h >> @@ -1249,6 +1249,7 @@ static inline void __set_task_cpu(struct task_struct *p, >> unsigned int cpu) >> #endif >> p->wake_cpu = cpu; >> #endif >> + rseq_migrate(p); >> } > > I think you want that in set_task_cpu(), right next to nr_migrations++. This would miss the __set_task_cpu() call from sched_fork() and wake_up_new_task(). Those cases are not accounted as explicit "migrations", but it does change the CPU of the current task. So if for some weird reason userspace wants to fork() while in a rseq critical section, we want to trigger a rseq restart. Note that rseq_fork() implies rseq_preempt(), but userspace can request to track only migrations for a given rseq critical section (by using the RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT flag), so the rseq_preempt() in rseq_fork() is not enough to restart if a migration between CPUs is done across a fork. An alternative to this would be to call rseq_migrate() in rseq_fork(). Thoughts ? Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com