linux-kernel - Re: [PATCH 1/8] x86: do not free zero sized per cpu areas

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Date:	Thu, 25 Mar 2010 15:29:00 -0700
From:	Joel Becker <Joel.Becker@...cle.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Ian Campbell <ian.campbell@...rix.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 1/8] x86: do not free zero sized per cpu areas

On Wed, Mar 24, 2010 at 03:37:02AM -0700, Yinghai Lu wrote:
> From: Ian Campbell <ian.campbell@...rix.com>
> 
> This avoids an infinite loop in free_early_partial().
> 
> Add a warning to free_early_partial to catch future problems.
> 
> -v5: put back start > end back into WARN_ONCE()
> -v6: use one line for if according to linus
> 
> Signed-off-by: Ian Campbell <ian.campbell@...rix.com>
> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ingo Molnar <mingo@...e.hu>

Tested-by: Joel Becker <joel.becker@...cle.com>

	I ran into this when moving my paravirt_ops PVMs to 2.6.34-rc1.
I turned on CONFIG_NO_BOOTMEM to try it because it was the default.  I
had to put earlyprintk=xen on the command line to debug the problem.
My boots hung after:

...
(early) Local APIC disabled by BIOS -- you can enable it with "lapic"
(early) APIC: disable apic facility
(early) APIC: switched to apic NOOP
(early) Allocating PCI resources starting at 78000000 (gap: 78000000:88000000)
(early) Booting paravirtualized kernel on Xen
(early) Xen version: 3.1.3-rc3
(early) setup_percpu: NR_CPUS:8 nr_cpumask_bits:8 nr_cpu_ids:2 nr_node_ids:1

	Bisecting narrowed the problem to fb90ef [early_res: Add
free_early_partial()].  Turning off CONFIG_NO_BOOTMEM allowed me to
boot.  I then hunted up references to this function, which found me this
patch.
	This patch successfully resolved the problem.

Joel

-- 

"The nice thing about egotists is that they don't talk about other
 people."
         - Lucille S. Harper

Joel Becker
Principal Software Developer
Oracle
E-mail: joel.becker@...cle.com
Phone: (650) 506-8127
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