Re: [PATCH] SUNRPC: remove the maximum number of retries in call_bind_status

[dai.ngo@oracle.com]

On 3/8/23 11:03 AM, dai.ngo@oracle.com wrote:
> On 3/8/23 10:50 AM, Chuck Lever III wrote:
>>
>>> On Mar 8, 2023, at 1:45 PM, Dai Ngo <dai.ngo@oracle.com> wrote:
>>>
>>> Currently call_bind_status places a hard limit of 3 to the number of
>>> retries on EACCES error. This limit was done to accommodate the 
>>> behavior
>>> of a buggy server that keeps returning garbage when the NLM daemon is
>>> killed on the NFS server. However this change causes problem for other
>>> servers that take a little longer than 9 seconds for the port mapper to
>>> become ready when the NFS server is restarted.
>>>
>>> This patch removes this hard coded limit and let the RPC handles
>>> the retry according to whether the export is soft or hard mounted.
>>>
>>> To avoid the hang with buggy server, the client can use soft mount for
>>> the export.
>>>
>>> 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>
>> Helen is the royal queen of ^C  ;-)
>>
>> Did you try ^C on a mount while it waits for a rebind?
>
> She uses a test script that restarts the NFS server while NLM lock test
> is running. The failure is random, sometimes it fails and sometimes it
> passes depending on when the LOCK/UNLOCK requests come in so I think
> it's hard to time it to do the ^C, but I will ask.

We did the test with ^C and here is what we found.

For synchronous RPC task the signal was delivered to the RPC task and
the task exit with -ERESTARTSYS from __rpc_execute as expected.

For asynchronous RPC task the process that invokes the RPC task to send
the request detected the signal in rpc_wait_for_completion_task and exits
with -ERESTARTSYS. However the async RPC was allowed to continue to run
to completion. So if the async RPC task was retrying an operation and
the NFS server was down, it will retry forever if this is a hard mount
or until the NFS server comes back up.

The question for the list is should we propagate the signal to the async
task via rpc_signal_task to stop its execution or just leave it alone as is.

-Dai

>
> Thanks,
> -Dai
>
>>
>>
>>> ---
>>> include/linux/sunrpc/sched.h | 3 +--
>>> net/sunrpc/clnt.c            | 3 ---
>>> net/sunrpc/sched.c           | 1 -
>>> 3 files changed, 1 insertion(+), 6 deletions(-)
>>>
>>> diff --git a/include/linux/sunrpc/sched.h 
>>> b/include/linux/sunrpc/sched.h
>>> index b8ca3ecaf8d7..8ada7dc802d3 100644
>>> --- a/include/linux/sunrpc/sched.h
>>> +++ b/include/linux/sunrpc/sched.h
>>> @@ -90,8 +90,7 @@ 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;
>>> };
>>>
>>> typedef void            (*rpc_action)(struct rpc_task *);
>>> diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
>>> index 0b0b9f1eed46..63b438d8564b 100644
>>> --- a/net/sunrpc/clnt.c
>>> +++ b/net/sunrpc/clnt.c
>>> @@ -2050,9 +2050,6 @@ call_bind_status(struct rpc_task *task)
>>>             status = -EOPNOTSUPP;
>>>             break;
>>>         }
>>> -        if (task->tk_rebind_retry == 0)
>>> -            break;
>>> -        task->tk_rebind_retry--;
>>>         rpc_delay(task, 3*HZ);
>>>         goto retry_timeout;
>>>     case -ENOBUFS:
>>> diff --git a/net/sunrpc/sched.c b/net/sunrpc/sched.c
>>> index be587a308e05..c8321de341ee 100644
>>> --- a/net/sunrpc/sched.c
>>> +++ b/net/sunrpc/sched.c
>>> @@ -817,7 +817,6 @@ 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;
>>>
>>>     /* starting timestamp */
>>>     task->tk_start = ktime_get();
>>> -- 
>>> 2.9.5
>>>
>> -- 
>> Chuck Lever
>>
>>