On Fri, Sep 12, 2014 at 10:21 AM, Jeff Layton <jeff.layton@xxxxxxxxxxxxxxx> wrote: > On Fri, 12 Sep 2014 09:36:00 -0400 > Jeff Layton <jlayton@xxxxxxxxxxxxxxx> wrote: > >> On Thu, 11 Sep 2014 16:28:36 -0400 >> Jeff Layton <jeff.layton@xxxxxxxxxxxxxxx> wrote: >> >> > On Thu, 11 Sep 2014 15:55:47 -0400 >> > "J. Bruce Fields" <bfields@xxxxxxxxxxxx> wrote: >> > >> > > On Mon, Sep 08, 2014 at 12:30:19PM -0400, Jeff Layton wrote: >> > > > From: Jeff Layton <jlayton@xxxxxxxxxxxxxxx> >> > > > >> > > > In order to allow knfsd's lock manager to lift its grace period early, >> > > > we need to figure out whether all clients have finished reclaiming >> > > > their state not. Unfortunately, the current code doesn't allow us to >> > > > ascertain this. All we track for each client is a timestamp that tells >> > > > us when the last "check" or "create" operation came in. >> > > > >> > > > We need to track the two timestamps separately. Add a new >> > > > "reclaim_complete" column to the database that tells us when the last >> > > > "create" operation came in. For now, we just insert "0" in that column >> > > > but a later patch will make it so that we insert a real timestamp for >> > > > v4.1+ client records. >> > > >> > > If I understand correctly, then nfsdcltrack has a bug here: we shouldn't >> > > be counting a 4.1 client as allowed to reclaim on the next boot until we >> > > get the RECLAIM_COMPLETE, but nfsdcltrack is allowing a 4.1 client to >> > > reclaim if all we got the previous boot was a reclaim open (a "check" >> > > operation). >> > > >> > > --b. >> > > >> > >> > Yeah, I guess so, with a bit of a clarification I think... >> > >> > We don't want to allow a v4.1 client to reclaim if it didn't send a >> > RECLAIM_COMPLETE prior to the last reboot *and* the grace period ended >> > prior to the last reboot. >> > >> > IOW, in the case where the reboot occurs before the grace period ends, >> > we don't want to clean out the and deny reclaims. FWIW, the legacy >> > client tracker got this very wrong -- if you did a couple of rapid >> > reboots in succession you couldn't reclaim once everything was back up. >> > >> > I'll have to ponder how best to fix that. Given that the logic required >> > is quite different between v4.0 and v4.1 clients, we may have to add yet >> > another column to the DB to track what sort of client this is. >> > >> >> This new requirement complicates things quite a bit. I'll have to >> respin both patchsets. >> >> I think we can fix this by ensuring that we clean out any v4.1+ clients >> that have not done a "create" since the start of the grace period >> during a "grace_done" upcall. For v4.0 clients, we can't do that of >> course since a v4.0 client may reclaim opens but never do a new one >> (and so may never send a "create" at all). >> >> That means that we'll need also to send something in the "check" upcall >> that indicates the client's minorversion. The good news is that we >> won't need a new column in the DB since the only timestamp that matters >> for v4.1+ clients is the "create" time. We can just avoid setting the >> time field for v4.1+ clients on the "check" upcall. >> >> Now that we need to send info about the minorversion in a "check", I >> may go back to sending an actual minorversion in the upcall's >> environment vars. It doesn't make sense to me to send a boolean about >> RECLAIM_COMPLETE when the client hasn't actually sent one. >> >> I'll get started on reworking this but I have no idea on an ETA just >> yet. Hopefully I can have something that works by next week sometime. >> > > This is actually a much larger can of worms than it originally looks. > Consider this: > > Server reboots and v4.1+ client reclaims a few records but never sends > a RECLAIM_COMPLETE (client bug or maybe some bad timing?). Grace period > eventually ends, and its record is purged from the DB. > > Now we have a client that has reclaimed some files but that has no > record on stable storage. > > One possibility is to prematurely expire v4.1+ clients that have not > sent a RECLAIM_COMPLETE when the grace period ends. > > That seems problematic though -- what about clients that just happen to > do an EXCHANGE_ID just before the grace period is going to end, and > that get expired before they can issue their RECLAIM_COMPLETE. Will > that be a problem for them? > > Thoughts? See RFC5661 section 8.4.3, which describes those edge conditions, and how to deal with them. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
