From owner-svn-src-head@FreeBSD.ORG Sat Jan 24 16:21:16 2015 Return-Path: Delivered-To: svn-src-head@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id B5B07FB6; Sat, 24 Jan 2015 16:21:16 +0000 (UTC) Received: from smtp2.ore.mailhop.org (smtp2.ore.mailhop.org [54.186.57.195]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 948B41C0; Sat, 24 Jan 2015 16:21:16 +0000 (UTC) Received: from [73.34.117.227] (helo=ilsoft.org) by smtp2.ore.mailhop.org with esmtpsa (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (Exim 4.82) (envelope-from ) id 1YF39G-0005T9-Tv; Sat, 24 Jan 2015 16:01:23 +0000 Received: from revolution.hippie.lan (revolution.hippie.lan [172.22.42.240]) by ilsoft.org (8.14.9/8.14.9) with ESMTP id t0OG1LMX027462; Sat, 24 Jan 2015 09:01:21 -0700 (MST) (envelope-from ian@freebsd.org) X-Mail-Handler: DuoCircle Outbound SMTP X-Originating-IP: 73.34.117.227 X-Report-Abuse-To: abuse@duocircle.com (see https://support.duocircle.com/support/solutions/articles/5000540958-duocircle-standard-smtp-abuse-information for abuse reporting information) X-MHO-User: U2FsdGVkX18iK+Wh6yD0LjWl746IcYuo Message-ID: <1422115281.1038.57.camel@freebsd.org> Subject: Re: svn commit: r277643 - in head/sys: arm/arm dev/mem i386/i386 mips/mips sparc64/sparc64 From: Ian Lepore To: Konstantin Belousov Date: Sat, 24 Jan 2015 09:01:21 -0700 In-Reply-To: <20150124154240.GV42409@kib.kiev.ua> References: <201501241251.t0OCpGa8053192@svn.freebsd.org> <1422111397.1038.53.camel@freebsd.org> <20150124154240.GV42409@kib.kiev.ua> Content-Type: text/plain; charset="us-ascii" X-Mailer: Evolution 3.12.8 FreeBSD GNOME Team Port Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 24 Jan 2015 16:21:16 -0000 On Sat, 2015-01-24 at 17:42 +0200, Konstantin Belousov wrote: > On Sat, Jan 24, 2015 at 07:56:37AM -0700, Ian Lepore wrote: > > On Sat, 2015-01-24 at 12:51 +0000, Konstantin Belousov wrote: > > > Author: kib > > > Date: Sat Jan 24 12:51:15 2015 > > > New Revision: 277643 > > > URL: https://svnweb.freebsd.org/changeset/base/277643 > > > > > > Log: > > > Remove Giant from /dev/mem and /dev/kmem. It is definitely not needed > > > for i386, and from the code inspection, nothing in the > > > arm/mips/sparc64 implementations depends on it. > > > > > > > I'm not sure I agree with that. On arm the memrw() implementation uses > > a single statically-allocated page of kva space into which it maps each > > physical page in turn in the main loop. What prevents preemption or > > multicore access to /dev/mem from trying to use that single page for > > multiple operations at once? > > I see, thank you for noting this. > > But, I do not think that Giant is a solution for the problem. uiomove() > call accesses userspace, which may fault and cause sleep. If the > thread sleeps, the Giant is automatically dropped, so there is no real > protection. > > I think dump exclusive sx around whole memrw() should be enough. > > I can revert the commit for now, or I can leave it as is while > writing the patch with sx and waiting for somebody review. What > would you prefer ? > > P.S. mips uses uiomove_fromphys(), avoiding transient mapping, > and sparc allocates KVA when needed. I had planned to look into this today or tomorrow, so no need to revert. I'll study the other implementations and see what works well for arm. -- Ian