From owner-svn-src-all@FreeBSD.ORG Fri Mar 28 01:43:37 2014 Return-Path: Delivered-To: svn-src-all@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id EB615488; Fri, 28 Mar 2014 01:43:37 +0000 (UTC) Received: from freefall.freebsd.org (freefall.freebsd.org [IPv6:2001:1900:2254:206c::16:87]) (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 BBBC965E; Fri, 28 Mar 2014 01:43:37 +0000 (UTC) Received: from xyf.my.dom (localhost [127.0.0.1]) by freefall.freebsd.org (8.14.8/8.14.8) with ESMTP id s2S1hZ3Q025053; Fri, 28 Mar 2014 01:43:36 GMT (envelope-from davidxu@freebsd.org) Message-ID: <5334D3F4.8080000@freebsd.org> Date: Fri, 28 Mar 2014 09:44:20 +0800 From: David Xu User-Agent: Mozilla/5.0 (X11; FreeBSD i386; rv:24.0) Gecko/20100101 Thunderbird/24.3.0 MIME-Version: 1.0 To: Mateusz Guzik Subject: Re: svn commit: r263755 - head/sys/kern References: <201403252330.s2PNUaei052956@svn.freebsd.org> <5333D70D.7050306@freebsd.org> <20140327083730.GA22942@dft-labs.eu> <5333E581.1000100@freebsd.org> <20140327145819.GA4730@dft-labs.eu> In-Reply-To: <20140327145819.GA4730@dft-labs.eu> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org, Mateusz Guzik X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.17 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 28 Mar 2014 01:43:38 -0000 On 2014/03/27 22:58, Mateusz Guzik wrote: > On Thu, Mar 27, 2014 at 04:46:57PM +0800, David Xu wrote: >> On 2014/03/27 16:37, Mateusz Guzik wrote: >>> On Thu, Mar 27, 2014 at 03:45:17PM +0800, David Xu wrote: >>>> I think the async process pointer can be cleared when a process exits >>>> by registering an event handler. please see attached patch. >>>> >>> >>> Sure, but I'm not very fond of this solution. >>> >>> This is a rather obscure bug you wont hit unless you explicitly try, >>> and even then you need root privs by default. >>> >> OK, but I don't like the bug exists in kernel. It is not obscure for me, >> I can run "shutdown now" command, and insert a device, and then the >> kernel will write garbage data into freed memory space. >> > > Not sure what you mean. devd does not use this feature, and even if it > did async_proc is cleared on close, which happens while signal delivery > is still legal. > Thers is no race conidtion when using lock to protect it. > That said, you are not going to encounter this bug unless you code > something up to specifically trigger it. > > fwiw, I think we could axe this feature if there was no way to fix it > without introducing a check for every process. > If you added a feature, you can not assume people won't use it. >>> As such writing a callback function which will be executed for all exiting >>> processes seems unjustified for me. >>> >>> Ideally we would get some mechanism which would allow to register >>> callbacks for events related to given entity. Then it could be used to >>> provide a "call this function when process p exits", amongst other things. >>> >> >> Yes, but the callback itself is cheap enough and is not worth to be >> per-entity entry. >> > > There is other code in the kernel which would benefit from such > functionality - dev/syscons/scmouse, dev/vt/vt_core.c, aio and possibly > more. > > As such I think this is worth pursuing. > I can not say more, it seems it is an extension.