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=-19.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 DA3D0C433DB for ; Fri, 5 Feb 2021 16:52:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 885CA64F2B for ; Fri, 5 Feb 2021 16:52:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233096AbhBEPLa (ORCPT ); Fri, 5 Feb 2021 10:11:30 -0500 Received: from mail.kernel.org ([198.145.29.99]:46006 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233071AbhBEPC3 (ORCPT ); Fri, 5 Feb 2021 10:02:29 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 15F17650B9; Fri, 5 Feb 2021 14:14:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1612534478; bh=Odyxa63MXuG7WjkuLwF8TZAevmechkqZY24cr0WpRMU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=usv4cYtfCi8Ckj+zN/5VvcrOxtYrFPCITKWbmYcAYHBP+zbh5yGQO0I0dZb+RRNmq cWxYQ8Z+crnDo1GJCWU9IQcoqvJ6ArUkaRE0xZceSsVc3sRy5+Vp/F5sXXGZcsht/Z +i+mW0R9Iko4fvkFfUcz+3+r1feFWdyChhOyvQGg= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "Peter Zijlstra (Intel)" , Valentin Schneider , Sasha Levin Subject: [PATCH 4.14 15/15] kthread: Extract KTHREAD_IS_PER_CPU Date: Fri, 5 Feb 2021 15:09:00 +0100 Message-Id: <20210205140650.351126636@linuxfoundation.org> X-Mailer: git-send-email 2.30.0 In-Reply-To: <20210205140649.733510103@linuxfoundation.org> References: <20210205140649.733510103@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Peter Zijlstra [ Upstream commit ac687e6e8c26181a33270efd1a2e2241377924b0 ] There is a need to distinguish geniune per-cpu kthreads from kthreads that happen to have a single CPU affinity. Geniune per-cpu kthreads are kthreads that are CPU affine for correctness, these will obviously have PF_KTHREAD set, but must also have PF_NO_SETAFFINITY set, lest userspace modify their affinity and ruins things. However, these two things are not sufficient, PF_NO_SETAFFINITY is also set on other tasks that have their affinities controlled through other means, like for instance workqueues. Therefore another bit is needed; it turns out kthread_create_per_cpu() already has such a bit: KTHREAD_IS_PER_CPU, which is used to make kthread_park()/kthread_unpark() work correctly. Expose this flag and remove the implicit setting of it from kthread_create_on_cpu(); the io_uring usage of it seems dubious at best. Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Valentin Schneider Tested-by: Valentin Schneider Link: https://lkml.kernel.org/r/20210121103506.557620262@infradead.org Signed-off-by: Sasha Levin --- include/linux/kthread.h | 3 +++ kernel/kthread.c | 27 ++++++++++++++++++++++++++- kernel/smpboot.c | 1 + 3 files changed, 30 insertions(+), 1 deletion(-) diff --git a/include/linux/kthread.h b/include/linux/kthread.h index 4e26609c77d41..eb305353f20fa 100644 --- a/include/linux/kthread.h +++ b/include/linux/kthread.h @@ -31,6 +31,9 @@ struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data), unsigned int cpu, const char *namefmt); +void kthread_set_per_cpu(struct task_struct *k, int cpu); +bool kthread_is_per_cpu(struct task_struct *k); + /** * kthread_run - create and wake a thread. * @threadfn: the function to run until signal_pending(current). diff --git a/kernel/kthread.c b/kernel/kthread.c index bd58765d75e76..fd6f9322312aa 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -433,11 +433,36 @@ struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data), return p; kthread_bind(p, cpu); /* CPU hotplug need to bind once again when unparking the thread. */ - set_bit(KTHREAD_IS_PER_CPU, &to_kthread(p)->flags); to_kthread(p)->cpu = cpu; return p; } +void kthread_set_per_cpu(struct task_struct *k, int cpu) +{ + struct kthread *kthread = to_kthread(k); + if (!kthread) + return; + + WARN_ON_ONCE(!(k->flags & PF_NO_SETAFFINITY)); + + if (cpu < 0) { + clear_bit(KTHREAD_IS_PER_CPU, &kthread->flags); + return; + } + + kthread->cpu = cpu; + set_bit(KTHREAD_IS_PER_CPU, &kthread->flags); +} + +bool kthread_is_per_cpu(struct task_struct *k) +{ + struct kthread *kthread = to_kthread(k); + if (!kthread) + return false; + + return test_bit(KTHREAD_IS_PER_CPU, &kthread->flags); +} + /** * kthread_unpark - unpark a thread created by kthread_create(). * @k: thread created by kthread_create(). diff --git a/kernel/smpboot.c b/kernel/smpboot.c index 5043e7433f4b1..eeb7f8e9cce37 100644 --- a/kernel/smpboot.c +++ b/kernel/smpboot.c @@ -187,6 +187,7 @@ __smpboot_create_thread(struct smp_hotplug_thread *ht, unsigned int cpu) kfree(td); return PTR_ERR(tsk); } + kthread_set_per_cpu(tsk, cpu); /* * Park the thread so that it could start right on the CPU * when it is available. -- 2.27.0