From: Theodore Ts'o <tytso@mit.edu>
Subject: Re: Call trace in ext4_es_lru_add on 3.10 stable
Date: Mon, 22 Sep 2014 12:47:15 -0400
Message-ID: <20140922164715.GB4572@thunk.org>
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 <20140918194311.GE19520@thunk.org>
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Cc: linux-ext4@vger.kernel.org,
	"p.herz@profihost.ag >> Philipp Herz - Profihost AG"
	<p.herz@profihost.ag>, stable@vger.kernel.org
To: Stefan Priebe <s.priebe@profihost.ag>
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On Mon, Sep 22, 2014 at 08:56:23AM +0200, Stefan Priebe wrote:
> >That's not the whole message; you just weren't able to capture it all.
> >How are you capturing these messages, by the way?  Serial console?
> 
> Sorry this was an incomplete copy and paste by me.
> 
> Here is the complete output:
> [1578544.839610] BUG: soft lockup - CPU#7 stuck for 22s! [mysqld:29281]
> [1578544.893450] Modules linked in: nf_conntrack_ipv4 nf_defrag_ipv4

OK, thanks, this is a known bug, where when ext4 is under heavy memory
pressure, we can end up stalling in reclaim.  This message indicates
that the system got stalled for 22 seconds, which is not good, since
it impacts the interactivity of your system, and increases the
long-tail latency of requests to servers running on your system, but
it doesn't cause any data loss or will cause any of your processes to
crash or otherwise stop functioning (except for temporarily).

It's something that we are working on, and there are patches which
Zheng Liu submitted that still need a bit of polishing, but I hope to
have it addressed soon.

Cheers,

						- Ted