linux-kernel - Re: [patch] add optimized generic percpu accessors

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Date:	Thu, 15 Jan 2009 14:39:16 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Tejun Heo <tj@...nel.org>
Cc:	roel kluin <roel.kluin@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>, Brian Gerst <brgerst@...il.com>,
	ebiederm@...ssion.com, cl@...ux-foundation.org,
	rusty@...tcorp.com.au, travis@....com,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	steiner@....com, hugh@...itas.com
Subject: Re: [patch] add optimized generic percpu accessors


* Ingo Molnar <mingo@...e.hu> wrote:

> FYI, -tip testing found the following bug with your percpu stuff:
> 
> There's an early exception during bootup, on 64-bit x86:
> 
>   PANIC: early exception 0e rip 10:ffffffff80276855: error ? cr2 6688
> 
>  - gcc version 4.3.2 20081007 (Red Hat 4.3.2-6) (GCC) 
>  - binutils-2.18.50.0.6-2.x86_64
> 
> config attached. You can find the disassembly of lock_release_holdtime() 
> below - that's where it crashed:

Gut feeling: we must have gotten a window where the PDA is not right. Note 
how it crashes in lock_release_holdtime() - that is CONFIG_LOCK_STAT 
instrumentation - very lowlevel and pervasive. Function tracing is also 
enabled although it should be inactive at the early stages.

So i'd take a good look at the PDA setup portion of the boot code, and see 
whether some spinlock acquire/release can slip in while the 
PDA/percpu-area is not reliable.

	Ingo
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