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=-3.5 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 07CA5C43331 for ; Wed, 13 Nov 2019 10:29:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D0214222C1 for ; Wed, 13 Nov 2019 10:29:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="TTy1nVtG" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727614AbfKMK3Z (ORCPT ); Wed, 13 Nov 2019 05:29:25 -0500 Received: from merlin.infradead.org ([205.233.59.134]:36280 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727491AbfKMK3U (ORCPT ); Wed, 13 Nov 2019 05:29:20 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=Content-Type:MIME-Version:References: Subject:Cc:To:From:Date:Message-Id:Sender:Reply-To:Content-Transfer-Encoding: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:In-Reply-To:List-Id:List-Help: List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=W0XG3ww6gZLvv2d/pinyx4OB+e9u6hzYaxWeYREhbw8=; b=TTy1nVtGpIkIdk9+MkixSWWOXp 2kDnPtge8CFMUKDvKFY1fzuHYJdNVE6pPpbQd2xsto/BSH2QMPz0JMYH83Ln3Oi669eap2r1SpiCF VCRESx2m0gjgjcVIkVH2kXbhX99gvA9SDDCZ1/uNJ0cpYCSmM/b45u9ebkgIPjh6uZ9MOB/LPy6LY KN7LGVLOwz1HnN8nm6ANd3RETz5jcQ/M/CiA3FU15C9f0mE86Td0zkdFh6aksKXXtwUZomXsSy/+Q txS4sutxTNvBTG+pDMnf8saphMfbyf02a7VtTJeioEy1AUpnL8iiS1rxvfhHfkDuY1S6kaSyDSUvd wqoqLJvQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1iUptf-0000X5-Fs; Wed, 13 Nov 2019 10:29:11 +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 71B47305FC2; Wed, 13 Nov 2019 11:28:01 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 0) id A14A329CF51EE; Wed, 13 Nov 2019 11:29:08 +0100 (CET) Message-Id: <20191113102855.868390100@infradead.org> User-Agent: quilt/0.65 Date: Wed, 13 Nov 2019 11:21:19 +0100 From: Peter Zijlstra To: peterz@infradead.org, mingo@kernel.org, will@kernel.org Cc: oleg@redhat.com, tglx@linutronix.de, linux-kernel@vger.kernel.org, bigeasy@linutronix.de, juri.lelli@redhat.com, williams@redhat.com, bristot@redhat.com, longman@redhat.com, dave@stgolabs.net, jack@suse.com Subject: [PATCH 4/5] locking/percpu-rwsem: Extract __percpu_down_read_trylock() References: <20191113102115.116470462@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In preparation for removing the embedded rwsem and building a custom lock, extract the read-trylock primitive. Signed-off-by: Peter Zijlstra (Intel) --- kernel/locking/percpu-rwsem.c | 21 ++++++++++++++------- 1 file changed, 14 insertions(+), 7 deletions(-) --- a/kernel/locking/percpu-rwsem.c +++ b/kernel/locking/percpu-rwsem.c @@ -45,7 +45,7 @@ void percpu_free_rwsem(struct percpu_rw_ } EXPORT_SYMBOL_GPL(percpu_free_rwsem); -bool __percpu_down_read(struct percpu_rw_semaphore *sem, bool try) +static bool __percpu_down_read_trylock(struct percpu_rw_semaphore *sem) { __this_cpu_inc(*sem->read_count); @@ -70,14 +70,21 @@ bool __percpu_down_read(struct percpu_rw * If !readers_block the critical section starts here, matched by the * release in percpu_up_write(). */ - if (likely(!smp_load_acquire(&sem->readers_block))) + if (likely(!atomic_read_acquire(&sem->readers_block))) return true; - /* - * Per the above comment; we still have preemption disabled and - * will thus decrement on the same CPU as we incremented. - */ - __percpu_up_read(sem); + __this_cpu_dec(*sem->read_count); + + /* Prod writer to re-evaluate readers_active_check() */ + rcuwait_wake_up(&sem->writer); + + return false; +} + +bool __percpu_down_read(struct percpu_rw_semaphore *sem, bool try) +{ + if (__percpu_down_read_trylock(sem)) + return true; if (try) return false;