Re: [PATCH 1/1] NFSD: cancel CB_RECALL_ANY call when nfs4_client is about to be destroyed

[Dai Ngo <dai.ngo@oracle.com>]

On 3/28/24 11:14 AM, Dai Ngo wrote:
>
> On 3/28/24 7:08 AM, Chuck Lever wrote:
>> On Wed, Mar 27, 2024 at 06:09:28PM -0700, Dai Ngo wrote:
>>> On 3/26/24 11:27 AM, Chuck Lever wrote:
>>>> On Tue, Mar 26, 2024 at 11:13:29AM -0700, Dai Ngo wrote:
>>>>> Currently when a nfs4_client is destroyed we wait for the 
>>>>> cb_recall_any
>>>>> callback to complete before proceed. This adds unnecessary delay 
>>>>> to the
>>>>> __destroy_client call if there is problem communicating with the 
>>>>> client.
>>>> By "unnecessary delay" do you mean only the seven-second RPC
>>>> retransmit timeout, or is there something else?
>>> when the client network interface is down, the RPC task takes ~9s to
>>> send the callback, waits for the reply and gets ETIMEDOUT. This process
>>> repeats in a loop with the same RPC task before being stopped by
>>> rpc_shutdown_client after client lease expires.
>> I'll have to review this code again, but rpc_shutdown_client
>> should cause these RPCs to terminate immediately and safely. Can't
>> we use that?
>
> rpc_shutdown_client works, it terminated the RPC call to stop the loop.
>
>>
>>
>>> It takes a total of about 1m20s before the CB_RECALL is terminated.
>>> For CB_RECALL_ANY and CB_OFFLOAD, this process gets in to a infinite
>>> loop since there is no delegation conflict and the client is allowed
>>> to stay in courtesy state.
>>>
>>> The loop happens because in nfsd4_cb_sequence_done if cb_seq_status
>>> is 1 (an RPC Reply was never received) it calls nfsd4_mark_cb_fault
>>> to set the NFSD4_CB_FAULT bit. It then sets cb_need_restart to true.
>>> When nfsd4_cb_release is called, it checks cb_need_restart bit and
>>> re-queues the work again.
>> Something in the sequence_done path should check if the server is
>> tearing down this callback connection. If it doesn't, that is a bug
>> IMO.

TCP terminated the connection after retrying for 16 minutes and
notified the RPC layer which deleted the nfsd4_conn.

But when nfsd4_run_cb_work ran again, it got into the infinite
loop caused by:
      /*
       * XXX: Ideally, we could wait for the client to
       *      reconnect, but I haven't figured out how
       *      to do that yet.
       */
       nfsd4_queue_cb_delayed(cb, 25);

which was introduced by c1ccfcf1a9bf. Note that I'm using 6.9-rc1.


-Dai

>
> I will check to see if TCP eventually closes the connection and
> notifies the RPC layer. From network traces, I see TCP stopped
> retrying after about 7 minutes. But even 7 minutes it's a long
> time we should not be hanging around waiting for it.
>
>>
>> Btw, have you checked NFSv4.0 behavior?
>
> Not yet.
>
>>
>>
>>>> I can see that a server shutdown might want to cancel these, but why
>>>> is this a problem when destroying an nfs4_client?
>>> Destroying an nfs4_client is called when the export is unmounted.
>> Ah, agreed. Thanks for reminding me.
>>
>>
>>> Cancelling these calls just make the process a bit quicker when there
>>> is problem with the client connection, or preventing the unmount to
>>> hang if there is problem at the workqueue and a callback work is
>>> pending there.
>>>
>>> For CB_RECALL, even if we wait for the call to complete the client
>>> won't be able to return any delegations since the nfs4_client is
>>> already been destroyed. It just serves as a notice to the client that
>>> there is a delegation conflict so it can take appropriate actions.
>>>
>>>>> This patch addresses this issue by cancelling the CB_RECALL_ANY 
>>>>> call from
>>>>> the workqueue when the nfs4_client is about to be destroyed.
>>>> Does CB_OFFLOAD need similar treatment?
>>> Probably. The copy is already done anyway, this is just a notification.
>> It would be a nicer design if all outstanding callback RPCs could
>> be handled with one mechanism instead of building a separate
>> shutdown method for each operation type.
>
> cb_recall ties to the individual delegation and cb_recall_any ties
> to the nfs4_client. We can check the delegation and the client to
> see if there are pending callbacks. Currently cb_offload is stand-alone
> and not tied to anything, kzalloc the callback on the fly and send
> it out so there is no way to find out if there is pending callback.
>
> -Dai
>
>>
>>
>>> -Dai
>>>
>>>>
>>>>> Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
>>>>> ---
>>>>>    fs/nfsd/nfs4callback.c | 10 ++++++++++
>>>>>    fs/nfsd/nfs4state.c    | 10 +++++++++-
>>>>>    fs/nfsd/state.h        |  1 +
>>>>>    3 files changed, 20 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c
>>>>> index 87c9547989f6..e5b50c96be6a 100644
>>>>> --- a/fs/nfsd/nfs4callback.c
>>>>> +++ b/fs/nfsd/nfs4callback.c
>>>>> @@ -1568,3 +1568,13 @@ bool nfsd4_run_cb(struct nfsd4_callback *cb)
>>>>>            nfsd41_cb_inflight_end(clp);
>>>>>        return queued;
>>>>>    }
>>>>> +
>>>>> +void nfsd41_cb_recall_any_cancel(struct nfs4_client *clp)
>>>>> +{
>>>>> +    if (test_bit(NFSD4_CLIENT_CB_RECALL_ANY, &clp->cl_flags) &&
>>>>> + cancel_delayed_work(&clp->cl_ra->ra_cb.cb_work)) {
>>>>> +        clear_bit(NFSD4_CLIENT_CB_RECALL_ANY, &clp->cl_flags);
>>>>> +        atomic_add_unless(&clp->cl_rpc_users, -1, 0);
>>>>> +        nfsd41_cb_inflight_end(clp);
>>>>> +    }
>>>>> +}
>>>>> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
>>>>> index 1a93c7fcf76c..0e1db57c9a19 100644
>>>>> --- a/fs/nfsd/nfs4state.c
>>>>> +++ b/fs/nfsd/nfs4state.c
>>>>> @@ -2402,6 +2402,7 @@ __destroy_client(struct nfs4_client *clp)
>>>>>        }
>>>>>        nfsd4_return_all_client_layouts(clp);
>>>>>        nfsd4_shutdown_copy(clp);
>>>>> +    nfsd41_cb_recall_any_cancel(clp);
>>>>>        nfsd4_shutdown_callback(clp);
>>>>>        if (clp->cl_cb_conn.cb_xprt)
>>>>>            svc_xprt_put(clp->cl_cb_conn.cb_xprt);
>>>>> @@ -2980,6 +2981,12 @@ static void force_expire_client(struct 
>>>>> nfs4_client *clp)
>>>>>        clp->cl_time = 0;
>>>>>        spin_unlock(&nn->client_lock);
>>>>> +    /*
>>>>> +     * no need to send and wait for CB_RECALL_ANY
>>>>> +     * when client is about to be destroyed
>>>>> +     */
>>>>> +    nfsd41_cb_recall_any_cancel(clp);
>>>>> +
>>>>>        wait_event(expiry_wq, atomic_read(&clp->cl_rpc_users) == 0);
>>>>>        spin_lock(&nn->client_lock);
>>>>>        already_expired = list_empty(&clp->cl_lru);
>>>>> @@ -6617,7 +6624,8 @@ deleg_reaper(struct nfsd_net *nn)
>>>>>            clp->cl_ra->ra_bmval[0] = BIT(RCA4_TYPE_MASK_RDATA_DLG) |
>>>>>                            BIT(RCA4_TYPE_MASK_WDATA_DLG);
>>>>>            trace_nfsd_cb_recall_any(clp->cl_ra);
>>>>> -        nfsd4_run_cb(&clp->cl_ra->ra_cb);
>>>>> +        if (!nfsd4_run_cb(&clp->cl_ra->ra_cb))
>>>>> +            clear_bit(NFSD4_CLIENT_CB_RECALL_ANY, &clp->cl_flags);
>>>>>        }
>>>>>    }
>>>>> diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
>>>>> index 01c6f3445646..259b4af7d226 100644
>>>>> --- a/fs/nfsd/state.h
>>>>> +++ b/fs/nfsd/state.h
>>>>> @@ -735,6 +735,7 @@ extern void nfsd4_change_callback(struct 
>>>>> nfs4_client *clp, struct nfs4_cb_conn *
>>>>>    extern void nfsd4_init_cb(struct nfsd4_callback *cb, struct 
>>>>> nfs4_client *clp,
>>>>>            const struct nfsd4_callback_ops *ops, enum nfsd4_cb_op 
>>>>> op);
>>>>>    extern bool nfsd4_run_cb(struct nfsd4_callback *cb);
>>>>> +extern void nfsd41_cb_recall_any_cancel(struct nfs4_client *clp);
>>>>>    extern int nfsd4_create_callback_queue(void);
>>>>>    extern void nfsd4_destroy_callback_queue(void);
>>>>>    extern void nfsd4_shutdown_callback(struct nfs4_client *);
>>>>> -- 
>>>>> 2.39.3
>>>>>
>
-- 
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