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 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.

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
>>>>