Hi Olga,
On Fri, 2020-04-17 at 11:15 -0400, Olga Kornievskaia wrote:
> When nconnect is used, SEQUENCE operation currently isn't bound to
> a particular transport. The problem is created on an idle mount,
> where SEQUENCE is the only operation being sent and opened TPC
> connections are slowly being close from the lack of use. If SEQUENCE
> is not assigned to the main connection, the main connection can
> be closed and with that so is the back channel bound to that
> connection.
>
> Since the only way client handles callback_path down is by sending
> BIND_CONN_TO_SESSION requesting to bind both backchannel and fore
> channel on the connection that was left going, but that connection
> was already bound to only forechannel. According to the spec, it's
> not allowed to change channel binding after they are done.
>
> The fix is to make sure that a lone SEQUENCE always goes on the
> main connection, keeping backchannel alive.
>
> Fixes: 5a0c257f8 ("NFS: send state management on a single
> connection")
> Signed-off-by: Olga Kornievskaia <kolga@xxxxxxxxxx>
> ---
> fs/nfs/nfs4proc.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
> index 99e9f2e..461f85d 100644
> --- a/fs/nfs/nfs4proc.c
> +++ b/fs/nfs/nfs4proc.c
> @@ -8857,7 +8857,7 @@ static struct rpc_task
> *_nfs41_proc_sequence(struct nfs_client *clp,
> .rpc_client = clp->cl_rpcclient,
> .rpc_message = &msg,
> .callback_ops = &nfs41_sequence_ops,
> - .flags = RPC_TASK_ASYNC | RPC_TASK_TIMEOUT,
> + .flags = RPC_TASK_ASYNC | RPC_TASK_TIMEOUT |
> RPC_TASK_NO_ROUND_ROBIN,
> };
> struct rpc_task *ret;
>
This works only in the case where the client is only sending SEQUENCE
instructions. There are other cases where it could be sending out other
operations that also renew the lease, but is doing it very
infrequently. Won't that also run into the same problem?
Is the fundamental problem here that we're not handling the
SEQ4_STATUS_CB_PATH_DOWN / SEQ4_STATUS_CB_PATH_DOWN_SESSION flags
correctly or is there something else going on?
--
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@xxxxxxxxxxxxxxx
