On Thu, 2012-04-12 at 11:42 -0400, Chuck Lever wrote:
> Hi-
>
> Changing the SETCLIENTID boot verifier so it is global for the whole client exposes a problem with how we allocate state owners.
>
> A quick umount / mount sequence destroys all state on the client. But since the client now always uses the same boot verifier and nfs_client_id4 string, the server no longer recognizes a client reboot. FOr a fresh mount, the client may perform a SETCLIENTID, but it is treated as a callback update (state is not purged) if the client's lease has not yet expired.
>
> Our state owners are generated from a pair of ida structures in the nfs_server for that mount. They always start from zero after a mount operation. Likewise, the sequence IDs for these state owners are also reset by umount / mount. Note that each mount point gets a fresh nfs_server, so these structures are not retained across umount / mount.
>
> This means umount / mount with no lease expiry starts to re-play state owners with reset sequence IDs. Servers don't really care for that behavior. I have a test case that reliably gets a BAD_SEQID error from a server after a quick umount / mount followed by a single file creation.
>
> Now that we are about to switch to using more-or-less global SETCLIENTID boot verifiers, it seems to me that we really want a global openowner_id and lockowner_id as well.
>
> The performance impact of such a change might be acceptable because we cache and reuse state owners now.
>
> Thoughts?
That's a definite server bug. If the client holds no open state, then it
is allowed to forget the open owner and start the sequence id from 0
again. It is not required to remember sequence ids for open owners that
aren't in use.
Our current client could easily trigger this bug even without a
umount/mount.
Cheers
Trond
--
Trond Myklebust
Linux NFS client maintainer
NetApp
Trond.Myklebust@xxxxxxxxxx
www.netapp.com
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