From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jiri Pirko Subject: Re: [PATCH v3 net-next 3/4] rocker: do not make neighbour entry changes when preparing transactions Date: Wed, 20 May 2015 13:17:36 +0200 Message-ID: <20150520111736.GE2228@nanopsycho.orion> References: <1432100902-10187-1-git-send-email-simon.horman@netronome.com> <1432100902-10187-4-git-send-email-simon.horman@netronome.com> <555C267B.9070807@lab.ntt.co.jp> <20150520074810.GA21934@vergenet.net> <555C4776.70508@lab.ntt.co.jp> <20150520084623.GA14454@vergenet.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Toshiaki Makita , Scott Feldman , David Miller , netdev@vger.kernel.org To: Simon Horman Return-path: Received: from mail-wi0-f173.google.com ([209.85.212.173]:36174 "EHLO mail-wi0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752467AbbETLRk (ORCPT ); Wed, 20 May 2015 07:17:40 -0400 Received: by wizk4 with SMTP id k4so151162119wiz.1 for ; Wed, 20 May 2015 04:17:39 -0700 (PDT) Content-Disposition: inline In-Reply-To: <20150520084623.GA14454@vergenet.net> Sender: netdev-owner@vger.kernel.org List-ID: Wed, May 20, 2015 at 10:46:26AM CEST, simon.horman@netronome.com wrote: >On Wed, May 20, 2015 at 05:36:06PM +0900, Toshiaki Makita wrote: >> On 2015/05/20 16:48, Simon Horman wrote: >> > On Wed, May 20, 2015 at 03:15:23PM +0900, Toshiaki Makita wrote: >> >> On 2015/05/20 14:48, Simon Horman wrote: >> ... >> >>> static void _rocker_neigh_add(struct rocker *rocker, >> >>> + enum switchdev_trans trans, >> >>> struct rocker_neigh_tbl_entry *entry) >> >>> { >> >>> + if (trans == SWITCHDEV_TRANS_PREPARE) >> >>> + return; >> >>> entry->index = rocker->neigh_tbl_next_index++; >> >> >> >> Isn't index needed here? It looks to be used in later function call and >> >> logging. >> > >> > Thanks, that does not follow the usual model of setting values >> > during the PREPARE (and all other) transaction phase(s). >> > >> >> How about setting index like this? >> >> >> >> entry->index = rocker->neigh_tbl_next_index; >> >> if (trans == PREPARE) >> >> return; >> >> rocker->neigh_tbl_next_index++; >> >> ... >> > >> > I am concerned that _rocker_neigh_add() may be called by some other >> > caller while a transaction is in process and thus entry->index will >> > be inconsistent across callers. >> > >> > Perhaps we can convince ourselves that all the bases are covered. >> > So far my testing has drawn a blank. But the logic seems difficult to >> > reason about. >> > >> > As we are basically allocating an index I suppose what is really needed for >> > a correct implementation is a transaction aware index allocator, like we >> > have for memory (rocker_port_kzalloc etc...). But that does seem like >> > overkill. >> > >> > I think that we can make entry->index consistent across >> > calls in the same transaction at the expense of breaking the >> > rule that per-transaction data should be set during all transaction phases. >> > >> > Something like this: >> > >> > >> > if (trans != SWITCHDEV_TRANS_COMMIT) >> > /* Avoid index being set to different values across calls >> > * to this function by the same caller within the same >> > * transaction. >> > */ >> > entry->index = rocker->neigh_tbl_next_index++; >> > if (trans == SWITCHDEV_TRANS_PREPARE) >> > return; >> > >> > >> >> As long as it is guraded by rtnl lock, no worries about this race? It >> seems to be assumed that prepare-commit is guarded by rtnl lock, >> according to commit c4f20321 ("rocker: support prepare-commit >> transaction model"). >> >> But as you are concerned, it seems to be able to be called by another >> caller, specifically, neigh_timer_handler() in interrupt context without >> rtnl lock. IMHO, it should be fixed rather than avoiding the race here. > >Yes, I believe that is the case I was seeing. > >Scott, Jiri, how would you like to resolve this? I believe that you can depend on rtnl being held - in switchdev_port_obj_add there is ASSERT_RTNL assection at the very beginning of the function.