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Date: Wed, 20 May 2015 17:36:06 +0900 From: Toshiaki Makita <makita.toshiaki@....ntt.co.jp> To: Simon Horman <simon.horman@...ronome.com> CC: Scott Feldman <sfeldma@...il.com>, Jiri Pirko <jiri@...nulli.us>, David Miller <davem@...emloft.net>, netdev@...r.kernel.org Subject: Re: [PATCH v3 net-next 3/4] rocker: do not make neighbour entry changes when preparing transactions 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. Thanks, Toshiaki Makita -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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