linux-kernel - Re: [PATCH 0/2] ia64: possible module unwind table optimisation

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Message-ID: <20100917084411.GC20325@esdhcp04044.research.nokia.com>
Date:	Fri, 17 Sep 2010 11:44:11 +0300
From:	Phil Carmody <ext-phil.2.carmody@...ia.com>
To:	ext Tony Luck <tony.luck@...el.com>
Cc:	"fenghua.yu@...el.com" <fenghua.yu@...el.com>,
	"linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/2] ia64: possible module unwind table optimisation

On 16/09/10 23:56 +0200, ext Tony Luck wrote:
> On Wed, Sep 15, 2010 at 3:22 PM, Phil Carmody
> <ext-phil.2.carmody@...ia.com> wrote:
> > Turn on kmemleak, or anything else which repeatedly runs up the stack just
> > for the fun of gathering backtraces. Kmemleak's what caused us to notice
> > the issue in our ARM-based environment.
> 
> kmemleak needs CONFIG_STACKTRACE - which I haven't got around to putting
> into ia64 yet.  I dug up an earlier attempt at doing so, and turned on kmemleak,
> but it crashes early in boot (before ever getting to my stack tracer)
> in possibly
> the first call to kmem_cache_alloc().  With SLUB the error is an unaligned
> reference to 0xffffffffffffffff, with SLAB I get a NULL deref.
> 
> :-(

This is a shame, but not a real problem in the context of my patch - you can't 
usefully optimise something that's seemingly almost never used. It can be filed
in the cylindrical filing cabinet.

Phil
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