linux-kernel - Re: [Linux-cachefs] 3.0.3 64-bit Crash running fscache/cachefilesd

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Date:	Thu, 13 Oct 2011 16:21:27 +0100
From:	David Howells <dhowells@...hat.com>
To:	Mark Moseley <moseleymark@...il.com>
Cc:	dhowells@...hat.com,
	Linux filesystem caching discussion list 
	<linux-cachefs@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [Linux-cachefs] 3.0.3 64-bit Crash running fscache/cachefilesd

Mark Moseley <moseleymark@...il.com> wrote:

> So on a cleared cache with SLAB, it took a while but this finally came
> up. One interesting thing is that at some point, it logged this:
> 
> [13461.605871] [httpd ] <== __fscache_read_or_alloc_pages() = -ENOBUFS
> [invalidating]

That's okay.  Basically, a read-from-cache operation was rejected because the
cache object was in the early phase of being invalidated.  I kept it simple
here - the read might complete next time it is tried, but it's just a cache so
that shouldn't matter.

> It was a while from when it logged that until when I happened to check
> on the box again, but when I did (shortly before this traceback),
> despite constant NFS activity, nothing in the fscache cache was
> getting written out (i.e. the used bytes on the partition stopped
> changing), and without any messages about withdrawing the cache or
> anythin.

Did you look at /proc/fs/fscache/stats at all?

> [20839.802118] kernel BUG at fs/fscache/object-list.c:83!
> [20839.802733] invalid opcode: 0000 [#1] SMP

That fits with the previous BUG elsewhere in object-list.c.  It sounds like
there's a refcounting problem somewhere.

David
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