On Mon, 2023-04-17 at 21:41 +0000, Chuck Lever III wrote:
>
>
> > On Apr 17, 2023, at 4:49 PM, Trond Myklebust
> > <trondmy@xxxxxxxxxxxxxxx> wrote:
> >
> > On Fri, 2023-04-07 at 20:30 -0700, Dai Ngo wrote:
> > > Currently call_bind_status places a hard limit of 9 seconds for
> > > retries
> > > on EACCES error. This limit was done to prevent the RPC request
> > > from
> > > being retried forever if the remote server has problem and never
> > > comes
> > > up
> > >
> > > However this 9 seconds timeout is too short, comparing to other
> > > RPC
> > > timeouts which are generally in minutes. This causes intermittent
> > > failure
> > > with EIO on the client side when there are lots of NLM activity
> > > and
> > > the
> > > NFS server is restarted.
> > >
> > > Instead of removing the max timeout for retry and relying on the
> > > RPC
> > > timeout mechanism to handle the retry, which can lead to the RPC
> > > being
> > > retried forever if the remote NLM service fails to come up. This
> > > patch
> > > simply increases the max timeout of call_bind_status from 9 to 90
> > > seconds
> > > which should allow enough time for NLM to register after a
> > > restart,
> > > and
> > > not retrying forever if there is real problem with the remote
> > > system.
> > >
> > > Fixes: 0b760113a3a1 ("NLM: Don't hang forever on NLM unlock
> > > requests")
> > > Reported-by: Helen Chao <helen.chao@xxxxxxxxxx>
> > > Tested-by: Helen Chao <helen.chao@xxxxxxxxxx>
> > > Signed-off-by: Dai Ngo <dai.ngo@xxxxxxxxxx>
> > > ---
> > > include/linux/sunrpc/clnt.h | 3 +++
> > > include/linux/sunrpc/sched.h | 4 ++--
> > > net/sunrpc/clnt.c | 2 +-
> > > net/sunrpc/sched.c | 3 ++-
> > > 4 files changed, 8 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/include/linux/sunrpc/clnt.h
> > > b/include/linux/sunrpc/clnt.h
> > > index 770ef2cb5775..81afc5ea2665 100644
> > > --- a/include/linux/sunrpc/clnt.h
> > > +++ b/include/linux/sunrpc/clnt.h
> > > @@ -162,6 +162,9 @@ struct rpc_add_xprt_test {
> > > #define RPC_CLNT_CREATE_REUSEPORT (1UL << 11)
> > > #define RPC_CLNT_CREATE_CONNECTED (1UL << 12)
> > >
> > > +#define RPC_CLNT_REBIND_DELAY 3
> > > +#define RPC_CLNT_REBIND_MAX_TIMEOUT 90
> > > +
> > > struct rpc_clnt *rpc_create(struct rpc_create_args *args);
> > > struct rpc_clnt *rpc_bind_new_program(struct rpc_clnt *,
> > > const struct rpc_program *, u32);
> > > diff --git a/include/linux/sunrpc/sched.h
> > > b/include/linux/sunrpc/sched.h
> > > index b8ca3ecaf8d7..e9dc142f10bb 100644
> > > --- a/include/linux/sunrpc/sched.h
> > > +++ b/include/linux/sunrpc/sched.h
> > > @@ -90,8 +90,8 @@ struct rpc_task {
> > > #endif
> > > unsigned char tk_priority : 2,/* Task priority
> > > */
> > > tk_garb_retry : 2,
> > > - tk_cred_retry : 2,
> > > - tk_rebind_retry : 2;
> > > + tk_cred_retry : 2;
> > > + unsigned char tk_rebind_retry;
> > > };
> > >
> > > typedef void (*rpc_action)(struct rpc_task *);
> > > diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
> > > index fd7e1c630493..222578af6b01 100644
> > > --- a/net/sunrpc/clnt.c
> > > +++ b/net/sunrpc/clnt.c
> > > @@ -2053,7 +2053,7 @@ call_bind_status(struct rpc_task *task)
> > > if (task->tk_rebind_retry == 0)
> > > break;
> > > task->tk_rebind_retry--;
> > > - rpc_delay(task, 3*HZ);
> > > + rpc_delay(task, RPC_CLNT_REBIND_DELAY * HZ);
> > > goto retry_timeout;
> > > case -ENOBUFS:
> > > rpc_delay(task, HZ >> 2);
> > > diff --git a/net/sunrpc/sched.c b/net/sunrpc/sched.c
> > > index be587a308e05..5c18a35752aa 100644
> > > --- a/net/sunrpc/sched.c
> > > +++ b/net/sunrpc/sched.c
> > > @@ -817,7 +817,8 @@ rpc_init_task_statistics(struct rpc_task
> > > *task)
> > > /* Initialize retry counters */
> > > task->tk_garb_retry = 2;
> > > task->tk_cred_retry = 2;
> > > - task->tk_rebind_retry = 2;
> > > + task->tk_rebind_retry = RPC_CLNT_REBIND_MAX_TIMEOUT /
> > > + RPC_CLNT_REBIND_DELAY;
> >
> > Why not just implement an exponential back off? If the server is
> > slow
> > to come up, then pounding the rpcbind service every 3 seconds isn't
> > going to help.
>
> Exponential backoff has the disadvantage that once we've gotten
> to the longer retry times, it's easy for a client to wait quite
> some time before it notices the rebind service is available.
>
> But I have to wonder if retrying every 3 seconds is useful if
> the request is going over TCP.
>
The problem isn't reliability: this is handling a case where we _are_
getting a reply from the server, just not one we wanted. EACCES here
means that the rpcbind server didn't return a valid entry for the
service we requested, presumably because the service hasn't been
registered yet.
So yes, an exponential back off is appropriate here.
--
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@xxxxxxxxxxxxxxx
