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=-20.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS 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 B8243C2B9F7 for ; Wed, 26 May 2021 07:16:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 921D8613F4 for ; Wed, 26 May 2021 07:16:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232922AbhEZHSB (ORCPT ); Wed, 26 May 2021 03:18:01 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:53206 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232648AbhEZHRz (ORCPT ); Wed, 26 May 2021 03:17:55 -0400 Date: Wed, 26 May 2021 07:16:22 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1622013383; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=RXiHf0c0cn4Kt1ZIBJQ7JRuAP5ixFIuY0yaPsrcQRMU=; b=zUaqO1+mcNXWI3RtMX17rLXa8hMlRUqvDckrkWsfUcbn39iv4gZWOTREoG0Y9e6K9USYQ+ pEmN+t3Dov2VH1w0qyyz9R5tWeApM22rMQGrFp/IFT6eOiK5+mJwC0SGFjNidjIVyzs3eJ k2nSQLAG0VcYizoAWEMotuIurcoPj9wbuim9ShyX9q0hbXD17BVpS3p4x5z2koZ94fB4qG 6eMicfyFG9QBb+gBjwRTxdCNrHrinASQuyQl7+IadQnp/ITYjrPE8fRvxkBYcuDlewlPdV EKmVelvA0Ba2rRk3mO+2RvFv/PikP57rmPK+plvr3KAB43G9E7wIzWbs+dTN1Q== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1622013383; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=RXiHf0c0cn4Kt1ZIBJQ7JRuAP5ixFIuY0yaPsrcQRMU=; b=Hmsj3CqJkoalw6itCOeD7073VJtg1DBNJ4ROmpV46x7zfPyKWqD2U+K+qaAkoiDx/5nqSS cRS5xIElFGft2xAQ== From: "tip-bot2 for Frederic Weisbecker" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: sched/core] sched: Stop PF_NO_SETAFFINITY from being inherited by various init system threads Cc: "Paul E. McKenney" , Frederic Weisbecker , Ingo Molnar , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20210525235849.441842-1-frederic@kernel.org> References: <20210525235849.441842-1-frederic@kernel.org> MIME-Version: 1.0 Message-ID: <162201338266.29796.17056048859247477492.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the sched/core branch of tip: Commit-ID: a8ea6fc9b089156d9230bfeef964dd9be101a4a9 Gitweb: https://git.kernel.org/tip/a8ea6fc9b089156d9230bfeef964dd9be101a4a9 Author: Frederic Weisbecker AuthorDate: Wed, 26 May 2021 01:58:49 +02:00 Committer: Ingo Molnar CommitterDate: Wed, 26 May 2021 08:58:53 +02:00 sched: Stop PF_NO_SETAFFINITY from being inherited by various init system threads Commit: 00b89fe0197f ("sched: Make the idle task quack like a per-CPU kthread") ... added PF_KTHREAD | PF_NO_SETAFFINITY to the idle kernel threads. Unfortunately these properties are inherited to the init/0 children through kernel_thread() calls: init/1 and kthreadd. There are several side effects to that: 1) kthreadd affinity can not be reset anymore from userspace. Also PF_NO_SETAFFINITY propagates to all kthreadd children, including the unbound kthreads Therefore it's not possible anymore to overwrite the affinity of any of them. Here is an example of warning reported by rcutorture: WARNING: CPU: 0 PID: 116 at kernel/rcu/tree_nocb.h:1306 rcu_bind_current_to_nocb+0x31/0x40 Call Trace: rcu_torture_fwd_prog+0x62/0x730 kthread+0x122/0x140 ret_from_fork+0x22/0x30 2) init/1 does an exec() in the end which clears both PF_KTHREAD and PF_NO_SETAFFINITY so we are fine once kernel_init() escapes to userspace. But until then, no initcall or init code can successfully call sched_setaffinity() to init/1. Also PF_KTHREAD looks legit on init/1 before it calls exec() but we better be careful with unknown introduced side effects. One way to solve the PF_NO_SETAFFINITY issue is to not inherit this flag on copy_process() at all. The cases where it matters are: * fork_idle(): explicitly set the flag already. * fork() syscalls: userspace tasks that shouldn't be concerned by that. * create_io_thread(): the callers explicitly attribute the flag to the newly created tasks. * kernel_thread(): - Fix the issues on init/1 and kthreadd - Fix the issues on kthreadd children. - Usermode helper created by an unbound workqueue. This shouldn't matter. In the worst case it gives more control to userspace on setting affinity to these short living tasks although this can be tuned with inherited unbound workqueues affinity already. Fixes: 00b89fe0197f ("sched: Make the idle task quack like a per-CPU kthread") Reported-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker Signed-off-by: Ingo Molnar Tested-by: Paul E. McKenney Link: https://lore.kernel.org/r/20210525235849.441842-1-frederic@kernel.org --- kernel/fork.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/fork.c b/kernel/fork.c index ace4631..e595e77 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -2000,7 +2000,7 @@ static __latent_entropy struct task_struct *copy_process( goto bad_fork_cleanup_count; delayacct_tsk_init(p); /* Must remain after dup_task_struct() */ - p->flags &= ~(PF_SUPERPRIV | PF_WQ_WORKER | PF_IDLE); + p->flags &= ~(PF_SUPERPRIV | PF_WQ_WORKER | PF_IDLE | PF_NO_SETAFFINITY); p->flags |= PF_FORKNOEXEC; INIT_LIST_HEAD(&p->children); INIT_LIST_HEAD(&p->sibling);