linux-kernel - Re: FS-Cache: Duplicate cookie detected

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Date:   Wed, 06 Mar 2019 17:20:03 +0000
From:   David Howells <dhowells@...hat.com>
To:     Christian Kujau <lists@...dbynature.de>
Cc:     dhowells@...hat.com, linux-kernel@...r.kernel.org,
        Anna Schumaker <anna.schumaker@...app.com>,
        Steve Dickson <steved@...hat.com>
Subject: Re: FS-Cache: Duplicate cookie detected

David Howells <dhowells@...hat.com> wrote:

> >  FS-Cache: Duplicate cookie detected
> >  FS-Cache: O-cookie c=000000009da9dbf0 [p=000000001593f904 fl=222 nc=0 na=1]
> >  FS-Cache: O-cookie d=00000000287febd9 n=00000000980c9e8a
> >  FS-Cache: O-key=[8] '020001bdc0a80064'
> >  FS-Cache: N-cookie c=00000000bfe3f869 [p=000000001593f904 fl=2 nc=0 na=1]
> >  FS-Cache: N-cookie d=00000000287febd9 n=00000000e153f178
> >  FS-Cache: N-key=[8] '020001bdc0a80064'
> 
> I've just spotted something that all these things have in common.  The old
> cookie has FSCACHE_COOKIE_RELINQUISHING set in the flags (fl=222).  I don't
> have a wait for this situation in fscache - which I should.

I take it back - 0x200 is FSCACHE_COOKIE_ACQUIRED. :-/

I can reproduce a slightly different problem by setting off ~6000 parallel
processes, each reading its own individual directory of files.

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