linux-kernel - Re: Linux 2.6.39-rc3

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Date:	Wed, 13 Apr 2011 11:51:39 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Joerg Roedel <joro@...tes.org>
CC:	Ingo Molnar <mingo@...e.hu>, Yinghai Lu <yinghai@...nel.org>,
	Alex Deucher <alexdeucher@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	dri-devel@...ts.freedesktop.org,
	Thomas Gleixner <tglx@...utronix.de>, Tejun Heo <tj@...nel.org>
Subject: Re: Linux 2.6.39-rc3

On 04/13/2011 10:21 AM, Joerg Roedel wrote:
> 
> First of all, I bisected between v2.6.37-rc2..f005fe12b90c which where
> only a couple of patches and merged v2.6.38-rc4 in at every step. There
> was no failure found.
> Then I tried this again, but this time I merged v2.6.38-rc5 at every
> step and was successful. The bad commit in this branch turned out to be
> 
> 	1a4a678b12c84db9ae5dce424e0e97f0559bb57c
> 
> which is related to memblock.
> 
> Then I tried to find out which change between 2.6.38-rc4 and 2.6.38-rc5
> is needed to trigger the failure, so I used f005fe12b90c as a base,
> bisected between v2.6.38-rc4..v2.6.38-rc5 and merged every bisect step
> into the base and tested. Here the bad commit turned out to be
> 
> 	e6d2e2b2b1e1455df16d68a78f4a3874c7b3ad20
> 
> which is related to gart. It turned out that the gart aperture on that
> box is on another position with these patches. Before it was as
> 0xa4000000 and now it is at 0xa0000000. It seems like this has something
> to do with the root-cause.
> 
> Reverting commit 1a4a678b12c84db9ae5dce424e0e97f0559bb57c fixes the
> problem btw. and booting with iommu=soft also works, but I have no idea
> yet why the aperture at that address is a problem (with the patch
> reverted the aperture lands at 0x80000000).
> 

Does reverting e6d2e2b2b1e1455df16d68a78f4a3874c7b3ad20 solve the
problem for you?

1a4a678b12c84db9ae5dce424e0e97f0559bb57c is a memory-allocation-order
patch, which have a nasty tendency to unmask bugs elsewhere in the
kernel.  However, e6d2e2b2b1e1455df16d68a78f4a3874c7b3ad20 looks
positively strange (and it doesn't exactly help that the description is
written in Yinghai-ese and is therefore nearly impossible to decode,
never mind tell if it is remotely correct.)

	-hpa


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