linux-kernel - Re: [PATCH] nfsd: always handle RPC_SIGNALLED earlier in nfsd4_cb_sequence

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Message-ID: <84527e1a-a163-49b3-8335-a551c2822929@oracle.com>
Date: Wed, 22 Jan 2025 11:06:19 -0500
From: Chuck Lever <chuck.lever@...cle.com>
To: Jeff Layton <jlayton@...nel.org>, Neil Brown <neilb@...e.de>,
        Olga Kornievskaia <okorniev@...hat.com>, Dai Ngo <Dai.Ngo@...cle.com>,
        Tom Talpey <tom@...pey.com>
Cc: linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nfsd: always handle RPC_SIGNALLED earlier in
 nfsd4_cb_sequence_done()

On 1/22/25 10:44 AM, Jeff Layton wrote:
> On Wed, 2025-01-22 at 10:20 -0500, Chuck Lever wrote:
>> On 1/22/25 10:10 AM, Jeff Layton wrote:
>>> The v4.0 client always restarts the callback when the connection is shut
>>> down (which is indicated by RPC_SIGNALLED()). The RPC is then requeued
>>> and the result eventually should complete (or be aborted).
>>>
>>> The v4.1 code instead processes the result and only later decides to
>>> restart the call. Even more problematic is the fact that it releases the
>>> slot beforehand. The restarted call may get a new slot, which would
>>> could break DRC handling.
>>
>> "break DRC handling" -- I'd like to understand this.
>>
>> NFSD always sets cachethis to false in CB_SEQUENCE, so there is no DRC
>> for these operations. The only thing the client saves is the slot
>> sequence number IIUC.
>>
>> Is retrying an uncached operation via a different slot a problem?
>>
> 
> Ahh, I missed that we always set cachethis to false. So, there is
> probably now a problem with the DRC after all. Still, I don't see a
> good argument for processing the CB_SEQUENCE result, when we intend to
> retransmit the call anyway.

I expect that the rationale is that the slot sequence number needs to be
advanced appropriately before the slot can be used again.


-- 
Chuck Lever