From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ido Schimmel Subject: Re: [patch net-next v2 09/11] ipv4: fib: Add an API to request a FIB dump Date: Wed, 23 Nov 2016 21:53:28 +0200 Message-ID: <20161123195328.aqzbhf263z2pq2e7@splinter> References: <1479911670-4525-1-git-send-email-jiri@resnulli.us> <1479911670-4525-10-git-send-email-jiri@resnulli.us> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Jiri Pirko , netdev@vger.kernel.org, davem@davemloft.net, idosch@mellanox.com, eladr@mellanox.com, yotamg@mellanox.com, nogahf@mellanox.com, arkadis@mellanox.com, ogerlitz@mellanox.com, roopa@cumulusnetworks.com, dsa@cumulusnetworks.com, nikolay@cumulusnetworks.com, andy@greyhouse.net, vivien.didelot@savoirfairelinux.com, andrew@lunn.ch, f.fainelli@gmail.com, alexander.h.duyck@intel.com, kaber@trash.net To: Hannes Frederic Sowa Return-path: Received: from out5-smtp.messagingengine.com ([66.111.4.29]:47787 "EHLO out5-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933854AbcKWUDg (ORCPT ); Wed, 23 Nov 2016 15:03:36 -0500 Content-Disposition: inline In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On Wed, Nov 23, 2016 at 06:47:03PM +0100, Hannes Frederic Sowa wrote: > Hmm, I think you need to read the sequence counter under rtnl_lock to > have an ordering with the rest of the updates to the RCU trie. Otherwise > you don't know if the fib trie has the correct view regarding to the > incoming notifications as a whole. This is also necessary during restarts. I spent quite a lot of time thinking about this specific issue, but I couldn't convince myself that the read should be done under RTNL and I'm not sure I understand your reasoning. Can you please elaborate? If, before each notification sent, we call atomic_inc() and then call atomic_read() at the end, then how can we be tricked? Thanks for looking into this!