On Wed, Aug 05, 2015 at 11:09:16AM +0200, Patrick McHardy wrote: > On 04.08, Pablo Neira Ayuso wrote: [...] > > Revisiting this scenario, this how this looks if we remove that check: > > > > preparation starts: > > > > add: table X (10), added to table list (now inactive) > > del: table X (11), inactive next. > > ^ > > gencursor > > > > commit starts (update gencursor): > > > > add: table X (01): clear past and report event, *NOTE*: the rule table is inactive. > > add: table X (01): delete from list and report event. > > ^ > > gencursor > > > > So it seems it should be fine to remove it as it is defensive. I think > > robots can generate this kind of command placing updates in a batch, > > anyway that should come in a follow up patch IMO. > > I don't follow. Why add an unnecessary check just to remove it again? > As I said, the only thing that matters is the next generation, we should > never even look at the current one when performing actions. Yes, we can remove those checks to reject add+del in the same batch in first place. I remember I added this because I found some problematic scenario, but given looking at the example above, I agree we can remove this first place. I'm going to recheck for other objects too. > > > > We shouldn't check if the object is active from the lookup function if > > > > we're in the middle of a transaction, since we hold the lock there is > > > > no way we can see inactive objects in the list. There's only one > > > > transaction at the same time. > > > > > > That's not entirely correct. Dump continuations happen asynchronously to > > > netlink modifications and commit operations, so the genid may bump in the > > > middle. We can get an inconsistent view if we have: > > > > > > dump set elements from set x table y > > > delete table y > > > create table y > > > create set x > > > begin commit > > > continue dump from new set > > > > We catch this from the nfnlhdr->res_id field in the nfnetlink message, > > but see below. > > > > > commit, send NEWGEN > > > > > > Sure, we will get a NEWGEN message, but at that time we might already have > > > sent a full message for the new table/set since that message is only send > > > after the commit is completed. > > > > I agree in that an event message at the beginning of the commit phase > > to announce the beginning new generation and another one to indicate > > of this transaction. > > > > - preparation phase - > > delete table y > > create table y > > create set x > > - commit phase - > > send NEWGEN, attribute type: begin > > delete table y > > create table y > > create set x > > send NEWGEN, attribute type: end > > > > Thanks for your feedback! > > That might work if the message ordering is then guaranteed. However I think > we can fix this case without changing NEWGEN. Let me think about that a bit, > for now just taking care of the genid checks correctly seems like a good > step forward. But we can catch this problem through ->res_id, OK? > BTW, we also need to adjust loop detection to only take into account > active rules, active chains, active sets etc. Indeed, thanks Patrick. Will you take care of this? It would be great to have a fix for these in this merge window. On top of that, I have a patchset here to add named expressions as you suggested as a generic way to implement named counters (or any other stateful expression) and I need that this is fixed first so I don't need to add another ugly _INACTIVE flag to the nft_nexpr object. Let me know, thanks! -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
