linux-kernel - Re: [PATCH] nfsd: remove long-standing revoked delegations by force

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Message-ID: <a35d7d19-c2ee-4d32-ae12-6d8493dbac0b@huawei.com>
Date: Tue, 2 Sep 2025 21:08:48 +0800
From: Li Lingfeng <lilingfeng3@...wei.com>
To: Benjamin Coddington <bcodding@...hat.com>
CC: Jeff Layton <jlayton@...nel.org>, <chuck.lever@...cle.com>,
	<neil@...wn.name>, <okorniev@...hat.com>, <Dai.Ngo@...cle.com>,
	<tom@...pey.com>, <linux-nfs@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <yukuai1@...weicloud.com>,
	<houtao1@...wei.com>, <yi.zhang@...wei.com>, <yangerkun@...wei.com>,
	<lilingfeng@...weicloud.com>, <zhangjian496@...wei.com>
Subject: Re: [PATCH] nfsd: remove long-standing revoked delegations by force

Hi, Ben

在 2025/9/2 20:43, Benjamin Coddington 写道:
> On 2 Sep 2025, at 8:10, Li Lingfeng wrote:
>
>> Our expected outcome was that the client would release the abnormal
>> delegation via TEST_STATEID/FREE_STATEID upon detecting its invalidity.
>> However, this problematic delegation is no longer present in the
>> client's server->delegations list—whether due to client-side timeouts or
>> the server-side bug [1].
> How does the client timeout TEST_STATEID - are you mounting with 'soft'?
I have never actually encountered a timeout; on 5.10, I triggered it by
forcibly injecting a timeout error.

--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -6509,6 +6509,10 @@ static void nfs4_delegreturn_prepare(struct 
rpc_task *task, void *data)
                         &d_data->args.seq_args,
                         &d_data->res.seq_res,
                         task);
+
+       printk("%s force inject err\n", __func__);
+       task->tk_rpc_status = -ETIMEDOUT;
+       rpc_exit(task, -ETIMEDOUT);
  }
> We should find the server-side bug and fix it rather than write code to
> paper over it.  I do think the synchronization of state here is a bit
> fragile and wish the protocol had a generation, sequence, or marker for
> setting SEQ4_STATUS_ bits..
I was able to reproduce a server-side bug by adding delays (without using
fault injection). The server-side bug is detailed in reference [1].
I would appreciate it if you could provide any suggestions for 
modifications.
>>> Should we instead just administratively evict the client since it's
>>> clearly not behaving right in this case?
>> Thanks for the suggestion. While administratively evicting the client would
>> certainly resolve the immediate delegation issue, I'm concerned that approach
>> might be a bit heavy-handed.
>> The problematic behavior seems isolated to a single delegation. Meanwhile,
>> the client itself likely has numerous other open files and active state on
>> the server. Forcing a complete client reconnect would tear down all that
>> state, which could cause significant application disruption and be perceived
>> as a service outage from the client's perspective.
>>
>> [1] https://lore.kernel.org/all/de669327-c93a-49e5-a53b-bda9e67d34a2@huawei.com/
> ^^ in this thread you reference v5.10 - there was a knfsd fix for a
> cl_revoked leak "3b816601e279", and there have been 3 or 4 fixes to fix
> problems and optimize the client walk of delegations since then.  Jeff
> pointed out that there have been fixes in these areas.  Are you finding this
> problem still with all those fixes included?
As shown in [1], the problem can be reproduced at master(commit 
b320789d6883),
I think all those fixes are included.

Thanks,
Lingfeng

>
> Ben
>
>