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Date:   Wed, 6 Mar 2019 09:56:17 -0800 (PST)
From:   Christian Kujau <lists@...dbynature.de>
To:     David Howells <dhowells@...hat.com>
cc:     linux-kernel@...r.kernel.org,
        Anna Schumaker <anna.schumaker@...app.com>,
        Steve Dickson <steved@...hat.com>
Subject: Re: FS-Cache: Duplicate cookie detected

On Wed, 6 Mar 2019, David Howells wrote:
> I can reproduce a slightly different problem by setting off ~6000 parallel
> processes, each reading its own individual directory of files.

Ususually I only see it shortly after mount, and only once, but I too can 
reproduce it with NFStest ([0], and there's a Fedora package too) via 
"nfstest_cache --server $SERVER --client `hostname`", which then produces 
a couple of these messages:

FS-Cache: Duplicate cookie detected
FS-Cache: O-cookie c=000000002fcc866b [p=00000000c10c6e18 fl=222 nc=0 na=1]
FS-Cache: O-cookie d=00000000d5ed73bb n=00000000076c9150
FS-Cache: O-key=[10] '040002000801c0a80073'
FS-Cache: N-cookie c=00000000e8d5dcd4 [p=00000000c10c6e18 fl=2 nc=0 na=1]
FS-Cache: N-cookie d=00000000d5ed73bb n=00000000a54e9705
FS-Cache: N-key=[10] '040002000801c0a80073'


...and the O-key does indeed seem to resemble the server address, 
somewhat:

 >>> s = "040002000801c0a80073";
 >>> bytes = ["".join(x) for x in zip(*[iter(s)]*2)]; bytes = [int(x, 16) for x in bytes]; print ".".join(str(x) for x in reversed(bytes))
 115.0.168.192.1.8.0.2.0.4
 ^^^^^^^^^^^^^

Mount options on that client are:

$ mount | grep nfs4
nfs:/usr/local/src on /usr/local/src type nfs4 (ro,relatime,vers=4.2,rsize=1048576,wsize=1048576,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,clientaddr=192.168.56.139,local_lock=none,addr=192.168.0.115)

...so FS-Cache ("fsc") isn't even used here. The server in that scenario 
is a current Fedora 29 installation.

HTH,
Christian.

[0] http://wiki.linux-nfs.org/wiki/index.php/NFStest

> 
> I also see reports like this:
> 
>    FS-Cache: Duplicate cookie detected
>    FS-Cache: O-cookie c=00000000db33ad59 [p=000000004bc53500 fl=218 nc=0 na=0]
>    FS-Cache: O-cookie d=          (null) n=          (null)
>    FS-Cache: O-cookie o=000000006cf6db4f
>    FS-Cache: O-key=[16] '0100010101000000e51fc6000323ae02'
>    FS-Cache: N-cookie c=00000000791c49d0 [p=000000004bc53500 fl=2 nc=0 na=1]
>    FS-Cache: N-cookie d=00000000e220fe14 n=00000000d4484489
>    FS-Cache: N-key=[16] '0100010101000000e51fc6000323ae02'
> 
> with no cookie def or netfs data and flags ACQUIRED, RELINQUISHED and
> INVALIDATING - which I can insert a wait for.
> 
> David

-- 
BOFH excuse #420:

Feature was not beta tested

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