Re: [PATCH] SUNRPC: increase max timeout for rebind to handle NFS server restart

[Trond Myklebust <trondmy@hammerspace.com>]

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@oracle.com>
> Tested-by: Helen Chao <helen.chao@oracle.com>
> Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
> ---
>  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.

>  
>         /* starting timestamp */
>         task->tk_start = ktime_get();

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com