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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 CBFC7C433E6 for ; Tue, 16 Feb 2021 09:38:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8DF6464DFF for ; Tue, 16 Feb 2021 09:38:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229991AbhBPJiC (ORCPT ); Tue, 16 Feb 2021 04:38:02 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45584 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229806AbhBPJhv (ORCPT ); Tue, 16 Feb 2021 04:37:51 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 06B1DC061574; Tue, 16 Feb 2021 01:37:11 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Transfer-Encoding: Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Sender:Reply-To:Content-ID:Content-Description; bh=6p6aP26uvaDys5m2iqcqs2Sq1c/nYDnkVqNjuyxRkDU=; b=Nk4MUsvviR9MIo25CvF38GBU6P HueibuWzMXbLsx5spRiXK/Folbl0pODU9941RNDDvdGqgpXmzjy+XIssHin4gBD797gR8i+2CiWsS 9rNh3U6F/8P9YMQY6P8erJIv5tuxOhuvYGDhouTECta/1hzgomSFVtfYUVB8PFrMQrWPJun1bxPxK F5UliehaGMyP6rxujPhSnZT1x9VYjuxdQ5M2cyYF/evDQemtzv8Z0dsy2On6A4eZsIleh4omSGPQF W5ijuSs/k6kq8DUN5Ye3nZYeP/C8DtVAKAcz0jQ+2sxAbBn89IkIUL9Noq6BYQT4PoZiUGODuLnVZ RDBbf8JQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94 #2 (Red Hat Linux)) id 1lBwl5-00GheO-QE; Tue, 16 Feb 2021 09:35:12 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 46AE63059DD; Tue, 16 Feb 2021 10:35:02 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 2CE432058CB0E; Tue, 16 Feb 2021 10:35:02 +0100 (CET) Date: Tue, 16 Feb 2021 10:35:02 +0100 From: Peter Zijlstra To: =?iso-8859-1?Q?Andr=E9?= Almeida Cc: Thomas Gleixner , Ingo Molnar , Darren Hart , linux-kernel@vger.kernel.org, Steven Rostedt , Sebastian Andrzej Siewior , kernel@collabora.com, krisman@collabora.com, pgriffais@valvesoftware.com, z.figura12@gmail.com, joel@joelfernandes.org, malteskarupke@fastmail.fm, linux-api@vger.kernel.org, fweimer@redhat.com, libc-alpha@sourceware.org, linux-kselftest@vger.kernel.org, shuah@kernel.org, acme@kernel.org, corbet@lwn.net Subject: Re: [RFC PATCH 01/13] futex2: Implement wait and wake functions Message-ID: References: <20210215152404.250281-1-andrealmeid@collabora.com> <20210215152404.250281-2-andrealmeid@collabora.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20210215152404.250281-2-andrealmeid@collabora.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 15, 2021 at 12:23:52PM -0300, André Almeida wrote: > +static int futex_dequeue_multiple(struct futexv_head *futexv, unsigned int nr) > +{ > + int i, ret = -1; > + > + for (i = 0; i < nr; i++) { > + spin_lock(&futexv->objects[i].bucket->lock); > + if (!list_empty_careful(&futexv->objects[i].list)) { > + list_del_init_careful(&futexv->objects[i].list); > + bucket_dec_waiters(futexv->objects[i].bucket); What's with the careful? AFAICT all sites have that bucket->lock. > + } else { > + ret = i; > + } > + spin_unlock(&futexv->objects[i].bucket->lock); > + } > + > + return ret; > +} > +static int futex_enqueue(struct futexv_head *futexv, unsigned int nr_futexes, > + int *awakened) > +{ > + int i, ret; > + u32 uval, *uaddr, val; > + struct futex_bucket *bucket; > + > +retry: > + set_current_state(TASK_INTERRUPTIBLE); > + > + for (i = 0; i < nr_futexes; i++) { > + uaddr = (u32 * __user)futexv->objects[i].uaddr; > + val = (u32)futexv->objects[i].val; > + > + bucket = futexv->objects[i].bucket; > + > + bucket_inc_waiters(bucket); > + spin_lock(&bucket->lock); > + > + ret = futex_get_user(&uval, uaddr); > + > + if (unlikely(ret)) { > + spin_unlock(&bucket->lock); > + > + bucket_dec_waiters(bucket); > + __set_current_state(TASK_RUNNING); > + *awakened = futex_dequeue_multiple(futexv, i); > + > + if (__get_user(uval, uaddr)) > + return -EFAULT; > + > + if (*awakened >= 0) > + return 1; > + > + goto retry; > + } > + > + if (uval != val) { > + spin_unlock(&bucket->lock); > + > + bucket_dec_waiters(bucket); > + __set_current_state(TASK_RUNNING); > + *awakened = futex_dequeue_multiple(futexv, i); > + > + if (*awakened >= 0) > + return 1; > + > + return -EAGAIN; > + } > + > + list_add_tail(&futexv->objects[i].list, &bucket->list); and here > + spin_unlock(&bucket->lock); > + } > + > + return 0; > +} > + > +static void futex_mark_wake(struct futex_waiter *waiter, > + struct futex_bucket *bucket, > + struct wake_q_head *wake_q) > +{ > + struct task_struct *task; > + struct futexv_head *parent = futex_get_parent((uintptr_t)waiter, > + waiter->index); > + lockdep_assert_held(&bucket->lock); > + parent->hint = true; > + task = parent->task; > + get_task_struct(task); > + list_del_init_careful(&waiter->list); and here > + wake_q_add_safe(wake_q, task); > + bucket_dec_waiters(bucket); > +}