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=-1.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_DBL_ABUSE_MALW 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 A5D22C2D0DB for ; Fri, 31 Jan 2020 15:18:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 75C8E20705 for ; Fri, 31 Jan 2020 15:18:26 +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="al+Fp398" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729253AbgAaPSZ (ORCPT ); Fri, 31 Jan 2020 10:18:25 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:50144 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729099AbgAaPSM (ORCPT ); Fri, 31 Jan 2020 10:18:12 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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=IcI3x8o7HZQnoP+HjD1skPBuEnJN1YCJ8o2S/TJ+pxU=; b=al+Fp398PU6xh2t9u29cEadZzk 4OmmwLv+ZxtRr3OLwcgjFGK54qCEVXdXvD0K9GQI1bpJasXM5L5+Rqn1w4aiSspnBXtY7uZ6dhTNo 5k/AiV3MtKUWAo6AFgObapoHbbCDTLlhZ1x1tTP+/H0fykzT6ilJHRGSAk25YoWXK/a7qjDrEssc+ 2rB6ATbknXZbW2kbJBpD8oAdM//8qXhbxqdh9o6K4SGRYTRMCmpDff4+4KpfrndB1V3khkIrNSPm6 ZhmVx6ZA2TQYZLaDKbuOllLUSo7aJVBMDkPmh7VXOoic5HVI9wQhtrVC8469E4jvOSwb6uZV6I94R fl2RXoIQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1ixY3W-00045b-Va; Fri, 31 Jan 2020 15:18:03 +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 052DD3062B3; Fri, 31 Jan 2020 16:16:15 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 0) id BF79D2B64DB7A; Fri, 31 Jan 2020 16:17:58 +0100 (CET) Message-Id: <20200131151540.098485539@infradead.org> User-Agent: quilt/0.65 Date: Fri, 31 Jan 2020 16:07:07 +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 -v2 4/7] locking/percpu-rwsem: Extract __percpu_down_read_trylock() References: <20200131150703.194229898@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) Tested-by: Juri Lelli --- kernel/locking/percpu-rwsem.c | 19 +++++++++++++------ 1 file changed, 13 insertions(+), 6 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); @@ -73,11 +73,18 @@ bool __percpu_down_read(struct percpu_rw if (likely(!smp_load_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;