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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 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 01FBACA9EC0 for ; Mon, 28 Oct 2019 15:55:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C6C6820717 for ; Mon, 28 Oct 2019 15:55:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390738AbfJ1PzU (ORCPT ); Mon, 28 Oct 2019 11:55:20 -0400 Received: from mx2.suse.de ([195.135.220.15]:50316 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726612AbfJ1PzU (ORCPT ); Mon, 28 Oct 2019 11:55:20 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id AACD6B2A0; Mon, 28 Oct 2019 15:55:18 +0000 (UTC) Date: Mon, 28 Oct 2019 08:53:54 -0700 From: Davidlohr Bueso To: eric@anholt.net, wahrenst@gmx.net Cc: gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, devel@driverdev.osuosl.org Subject: Re: [PATCH] staging: vc04_services: replace g_free_fragments_mutex with spinlock Message-ID: <20191028155354.s3bgq2wazwlh32km@linux-p48b> References: <20191027221530.12080-1-dave@stgolabs.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20191027221530.12080-1-dave@stgolabs.net> User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Cc devel@driverdev.osuosl.org On Sun, 27 Oct 2019, Bueso wrote: >There seems no need to be using a semaphore, or a sleeping lock >in the first place: critical region is extremely short, does not >call into any blocking calls and furthermore lock and unlocking >operations occur in the same context. > >Get rid of another semaphore user by replacing it with a spinlock. > >Signed-off-by: Davidlohr Bueso >--- >This is in an effort to further reduce semaphore users in the kernel. > > .../staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c | 10 +++++----- > 1 file changed, 5 insertions(+), 5 deletions(-) > >diff --git a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c >index 8dc730cfe7a6..710d21654128 100644 >--- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c >+++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c >@@ -63,7 +63,7 @@ static char *g_free_fragments; > static struct semaphore g_free_fragments_sema; > static struct device *g_dev; > >-static DEFINE_SEMAPHORE(g_free_fragments_mutex); >+static DEFINE_SPINLOCK(g_free_fragments_lock); > > static irqreturn_t > vchiq_doorbell_irq(int irq, void *dev_id); >@@ -528,11 +528,11 @@ create_pagelist(char __user *buf, size_t count, unsigned short type) > > WARN_ON(g_free_fragments == NULL); > >- down(&g_free_fragments_mutex); >+ spin_lock(&g_free_fragments_lock); > fragments = g_free_fragments; > WARN_ON(fragments == NULL); > g_free_fragments = *(char **) g_free_fragments; >- up(&g_free_fragments_mutex); >+ spin_unlock(&g_free_fragments_lock); > pagelist->type = PAGELIST_READ_WITH_FRAGMENTS + > (fragments - g_fragments_base) / g_fragments_size; > } >@@ -591,10 +591,10 @@ free_pagelist(struct vchiq_pagelist_info *pagelistinfo, > kunmap(pages[num_pages - 1]); > } > >- down(&g_free_fragments_mutex); >+ spin_lock(&g_free_fragments_lock); > *(char **)fragments = g_free_fragments; > g_free_fragments = fragments; >- up(&g_free_fragments_mutex); >+ spin_unlock(&g_free_fragments_lock); > up(&g_free_fragments_sema); > } > >-- >2.16.4 >