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Subject: Re: once again problems with interrupted slots
To:     Olga Kornievskaia <aglo@umich.edu>,
        Trond Myklebust <trond.myklebust@hammerspace.com>
Cc:     linux-nfs <linux-nfs@vger.kernel.org>
References: <CAN-5tyFCotATeYVR0J1B_UaxhXYBDhp21LbFEzZtLYmgN_i+hg@mail.gmail.com>
From:   Tom Talpey <tom@talpey.com>
Message-ID: <13bed646-39b7-197e-ff90-85f8af10d93c@talpey.com>
Date:   Fri, 5 Jun 2020 08:06:14 -0400
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On 6/4/2020 5:21 PM, Olga Kornievskaia wrote:
> Hi Trond,
> 
> There is a problem with interrupted slots (yet again).
> 
> We send an operation to the server and it gets interrupted by the a signal.
> 
> We used to send a sole SEQUENCE to remove the problem of having real
> operation get an out of the cache reply and failing. Now we are not
> doing it again (since 3453d5708 NFSv4.1: Avoid false retries when RPC
> calls are interrupted"). So the problem is
> 
> We bump the sequence on the next use of the slot, and get SEQ_MISORDERED.

Misordered? It sounds like the client isn't managing the sequence
number, or perhaps the server never saw the original request, and
is being overly strict.

> We decrement the number back to the interrupted operation. This gets
> us a reply out of the cache. We again fail with REMOTE EIO error.

Ew. The client *decrements* the sequence?

Tom.

> Going back to the commit's message. I don't see the logic that the
> server can't tell if this is a new call or the old one. We used to
> send a lone SEQUENCE as a way to protect reuse of slot by a normal
> operation. An interrupted slot couldn't have been another SEQUENCE. So
> I don't see how the server can't tell a difference between SEQUENCE
> and any other operations.
> 
>