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=-9.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,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 B8899C55ABD for ; Tue, 10 Nov 2020 11:39:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 57C6620781 for ; Tue, 10 Nov 2020 11:39:29 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="P0bW5CTK"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="DxubOoMv" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731767AbgKJLj2 (ORCPT ); Tue, 10 Nov 2020 06:39:28 -0500 Received: from Galois.linutronix.de ([193.142.43.55]:57842 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727731AbgKJLjC (ORCPT ); Tue, 10 Nov 2020 06:39:02 -0500 From: Sebastian Andrzej Siewior DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1605008340; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=uKjEOEwu+WoojU3QuhjqfgE/KsmyANj68Ljnz4hnlYA=; b=P0bW5CTKDetrZt9TXP2gB+3wHgqg/LGdD+zJJnP0Qqgsztnrz6egrN7IESMUyghdnSQ7qS LSGHZpDgEPrWb/LmI/7XX2iTtcu5VVcDKGmO+tbt5Uju5QHxFCib/111tJcjI9agWEolOD Xps1CeHC4C8bWFjrjSuSa8BLxaMqQWETtskNaqGCYAIoa9PHi3vKsKw47sz/52jlvVACzl V2rLOM78iRWMcu9vdP/fobzSEDMOZy/vZ105oC5hO9qGzYIVWG5VXiVEgqjK8vxmvtOmoG KGWqCaLkR66alecGs9yfVb3LBrQerr6bthpw9aiRrLvRHq1YCneT2eXtwIM2Xw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1605008340; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=uKjEOEwu+WoojU3QuhjqfgE/KsmyANj68Ljnz4hnlYA=; b=DxubOoMvgf9vDlBYhz9lQp1NvZjxpEUruZ077jIsg7oWW4AqJxGuOWm0LH2kcHZjF/N1aa ZhYT3kyOadYqGuBw== To: linux-kernel@vger.kernel.org Cc: Thomas Gleixner , Peter Zijlstra , Ben Skeggs , Mike Galbraith , Sebastian Andrzej Siewior Subject: [PATCH 1/2] kthread: Move prio/affinite change into the newly created thread Date: Tue, 10 Nov 2020 12:38:47 +0100 Message-Id: <20201110113848.801379-2-bigeasy@linutronix.de> In-Reply-To: <20201110113848.801379-1-bigeasy@linutronix.de> References: <20201110113848.801379-1-bigeasy@linutronix.de> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org With enabled threaded interrupts the nouveau driver reported the following: | Chain exists of: | &mm->mmap_lock#2 --> &device->mutex --> &cpuset_rwsem | | Possible unsafe locking scenario: | | CPU0 CPU1 | ---- ---- | lock(&cpuset_rwsem); | lock(&device->mutex); | lock(&cpuset_rwsem); | lock(&mm->mmap_lock#2); The device->mutex is nvkm_device::mutex. Unblocking the lockchain at `cpuset_rwsem' is probably the easiest thing to do. Move the priority reset to the start of the newly created thread. Fixes: 710da3c8ea7df ("sched/core: Prevent race condition between cpuset an= d __sched_setscheduler()") Reported-by: Mike Galbraith Signed-off-by: Sebastian Andrzej Siewior Link: https://lkml.kernel.org/r/a23a826af7c108ea5651e73b8fbae5e653f16e86.ca= mel@gmx.de --- kernel/kthread.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) diff --git a/kernel/kthread.c b/kernel/kthread.c index 933a625621b8d..4a31127c6efbf 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -243,6 +243,7 @@ EXPORT_SYMBOL_GPL(kthread_parkme); =20 static int kthread(void *_create) { + static const struct sched_param param =3D { .sched_priority =3D 0 }; /* Copy data: it's on kthread's stack */ struct kthread_create_info *create =3D _create; int (*threadfn)(void *data) =3D create->threadfn; @@ -273,6 +274,13 @@ static int kthread(void *_create) init_completion(&self->parked); current->vfork_done =3D &self->exited; =20 + /* + * The new thread inherited kthreadd's priority and CPU mask. Reset + * back to default in case they have been changed. + */ + sched_setscheduler_nocheck(current, SCHED_NORMAL, ¶m); + set_cpus_allowed_ptr(current, housekeeping_cpumask(HK_FLAG_KTHREAD)); + /* OK, tell user we're spawned, wait for stop or wakeup */ __set_current_state(TASK_UNINTERRUPTIBLE); create->result =3D current; @@ -370,7 +378,6 @@ struct task_struct *__kthread_create_on_node(int (*thre= adfn)(void *data), } task =3D create->result; if (!IS_ERR(task)) { - static const struct sched_param param =3D { .sched_priority =3D 0 }; char name[TASK_COMM_LEN]; =20 /* @@ -379,13 +386,6 @@ struct task_struct *__kthread_create_on_node(int (*thr= eadfn)(void *data), */ vsnprintf(name, sizeof(name), namefmt, args); set_task_comm(task, name); - /* - * root may have changed our (kthreadd's) priority or CPU mask. - * The kernel thread should not inherit these properties. - */ - sched_setscheduler_nocheck(task, SCHED_NORMAL, ¶m); - set_cpus_allowed_ptr(task, - housekeeping_cpumask(HK_FLAG_KTHREAD)); } kfree(create); return task; --=20 2.29.2