From mboxrd@z Thu Jan 1 00:00:00 1970 From: Cong Wang Subject: Re: Q: what protects dev->napi_list? Date: Fri, 24 Aug 2012 18:39:13 +0800 Message-ID: <1345804753.11584.43.camel@cr0> References: <1345801604.11584.24.camel@cr0> <1345803142.29722.20.camel@edumazet-glaptop> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, Sylvain Munaut , David Miller To: Eric Dumazet Return-path: Received: from mx1.redhat.com ([209.132.183.28]:1949 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752217Ab2HXKjU (ORCPT ); Fri, 24 Aug 2012 06:39:20 -0400 In-Reply-To: <1345803142.29722.20.camel@edumazet-glaptop> Sender: netdev-owner@vger.kernel.org List-ID: On Fri, 2012-08-24 at 12:12 +0200, Eric Dumazet wrote: > On Fri, 2012-08-24 at 17:46 +0800, Cong Wang wrote: > > Hi, > > > > Sylvain reported a netpoll CPU stall > > http://marc.info/?l=linux-netdev&m=134563282530588&w=2 > > > > I tried to provide some fix for it: > > http://marc.info/?l=linux-netdev&m=134571069921429&w=2 > > > > When reviewing that code, I noticed a problem, it seems dev->napi_list > > is not protected by any lock? What if the device driver calls > > netif_napi_del() meanwhile we are iterating &dev->napi_list in > > poll_napi()? It seems netif_napi_del()/netif_napi_add() are usually > > called with the RTNL lock held during driver init/uninit, but again > > poll_napi() doesn't have RTNL lock. > > > > Of course poll_napi() cant try to get RTNL (its a mutex by the way) > > There are no problems, since : > > netif_napi_add() is called at device open time (before napi_poll() can > use it) > > netif_napi_del() at device dismantle time (after making sure napi_poll() > wont use the device again) Yeah, but bnx2 driver calls it at other time too, for example bnx2_change_ring_size() which in turn could be called by bnx2_set_channels().