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=-8.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,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 D71D5CA9EC0 for ; Mon, 28 Oct 2019 16:24:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A9948214E0 for ; Mon, 28 Oct 2019 16:24:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1572279857; bh=9SYnGJBKGry8Ep/RmYvXUU7PE75/rx3zjc6eQOr/ZoU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=rQYO41Dju5Mdol8nhHM7BG6aGkBSE3b0G55WLmMEX33CpGpdI2chXLlC0yulUpDL9 c2SNhKtDYpe2hoDcV9HaJGY0snO5sQbXlDPdXjnkU5PzGVO/zq9KnUBwBTFY4WuFun DEWxRxZCdvp9BU03fVSdYY6v3niB+kmktKiih+fY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390901AbfJ1QYQ (ORCPT ); Mon, 28 Oct 2019 12:24:16 -0400 Received: from mail.kernel.org ([198.145.29.99]:42222 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728653AbfJ1QYQ (ORCPT ); Mon, 28 Oct 2019 12:24:16 -0400 Received: from localhost (100.50.158.77.rev.sfr.net [77.158.50.100]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id C9FB9214E0; Mon, 28 Oct 2019 16:24:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1572279855; bh=9SYnGJBKGry8Ep/RmYvXUU7PE75/rx3zjc6eQOr/ZoU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=IIOmHNqdIHOz+TOlaGKmDotsgeOIVao8TqVGu+dbGb6mmOWZ70bF6X17X86o5xrLc /T3pzH6rM1uUpzHUhpbC5KVykYGhV2YFfs6PNmoua+la/jkFHGX81u1SzXAdYDj3SN omsFCnSD+LDNRZV+1JPIBhn57cqcBH6WZxCIMHjA= Date: Mon, 28 Oct 2019 17:24:12 +0100 From: Greg KH To: Davidlohr Bueso Cc: eric@anholt.net, wahrenst@gmx.net, devel@driverdev.osuosl.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] staging: vc04_services: replace g_free_fragments_mutex with spinlock Message-ID: <20191028162412.GA321492@kroah.com> References: <20191027221530.12080-1-dave@stgolabs.net> <20191028155354.s3bgq2wazwlh32km@linux-p48b> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191028155354.s3bgq2wazwlh32km@linux-p48b> User-Agent: Mutt/1.12.2 (2019-09-21) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 28, 2019 at 08:53:54AM -0700, Davidlohr Bueso wrote: > 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 > > This is obviously not in a format I can apply it in :(