From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiederm@xmission.com (Eric W. Biederman) Subject: Re: [RFC PATCH 1/2] netpoll: Remove dead netpoll_rx code Date: Thu, 13 Mar 2014 13:46:17 -0700 Message-ID: <87eh256d46.fsf@xmission.com> References: <1394540961.21721.22.camel@edumazet-glaptop2.roam.corp.google.com> <20140311082312.5ad00119@nehalam.linuxnetplumber.net> <87eh28cvi6.fsf@xmission.com> <20140313.152311.1995854418463980325.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain Cc: stephen@networkplumber.org, eric.dumazet@gmail.com, netdev@vger.kernel.org, xiyou.wangcong@gmail.com, mpm@selenic.com, satyam.sharma@gmail.com To: David Miller Return-path: Received: from out01.mta.xmission.com ([166.70.13.231]:40956 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755040AbaCMUqZ (ORCPT ); Thu, 13 Mar 2014 16:46:25 -0400 In-Reply-To: <20140313.152311.1995854418463980325.davem@davemloft.net> (David Miller's message of "Thu, 13 Mar 2014 15:23:11 -0400 (EDT)") Sender: netdev-owner@vger.kernel.org List-ID: David Miller writes: > From: ebiederm@xmission.com (Eric W. Biederman) > Date: Tue, 11 Mar 2014 13:48:01 -0700 > >> To play devil's advocate to my own patch. Does anyone know where kgdb >> over network (kgdboe) code lives today? >> >> What little I could find in a quick google search strongly suggests that >> kgdboe was abandoned in 2010 or so. >> >> I am trying to figure out if there are any active out of tree projects >> that need by directional netpoll. > > Good questions. > > I, perhaps mistakenly, kept the functionality around because there > were claims that we'd use it in-tree. > > That of course never materialized. > > The fact that people have a lot of trouble even finding the kgdboe > sources is quite telling, indeed. Also telling is that we actually broken kgdboe support in 2011 when netpoll_poll was removed. > Let's kill it, we can pull it back in (perhaps with a better design) > if something is proposed in-tree that will need it. Sounds good. Patches to follow shortly. > But I'm skeptical we ever will need it, and even if such a > reinstatement is proposed f.e. for the kgdboe use case it has holes. > > Consider the case where kgdboe takes a breakpoint in a hardware > interrupt handler. What happens? We cannot allow it to perform a > full back-and-forth conversation with the remote gdb from such a > context. In interests of full disclosure I missed a subtle detail, and what the code does today is that when netpoll_poll_dev is running is that it intercepts and drops all in-coming packets. So I think the current packet receive design might be salvaged, if someone gets interested again. The bitrot is pretty significant currently. Still I should point out that the code that drops received skbs is technically wrong today. It uses kfree_skb, instead of the needed dev_kfree_skb_any that is needed to work in any context netpoll_rx might be called in. Eric