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 3/26/24 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.

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.

> 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.
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.

-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
>>