linux-kernel - Re: [tip:x86/alternatives] x86, alternatives: Use 16-bit numbers for cpufeature index

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Message-ID: <20100629091535.GA28302@elte.hu>
Date:	Tue, 29 Jun 2010 11:15:35 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, hpa@...ux.intel.com
Cc:	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/alternatives] x86, alternatives: Use 16-bit numbers for
 cpufeature index


* tip-bot for tip-bot for H. Peter Anvin <hpa@...ux.intel.com> wrote:

> Commit-ID:  5dc71d49a7c209b77cd257049a2cdb99ed1008c0
> Gitweb:     http://git.kernel.org/tip/5dc71d49a7c209b77cd257049a2cdb99ed1008c0
> Author:     tip-bot for H. Peter Anvin <hpa@...ux.intel.com>
> AuthorDate: Thu, 10 Jun 2010 00:10:43 +0000
> Committer:  H. Peter Anvin <hpa@...or.com>
> CommitDate: Thu, 10 Jun 2010 23:20:34 -0700
> 
> x86, alternatives: Use 16-bit numbers for cpufeature index
> 
> We already have cpufeature indicies above 255, so use a 16-bit number
> for the alternatives index.  This consumes a padding field and so
> doesn't add any size, but it means that abusing the padding field to
> create assembly errors on overflow no longer works.  We can retain the
> test simply by redirecting it to the .discard section, however.
> 
> Signed-off-by: H. Peter Anvin <hpa@...ux.intel.com>
> LKML-Reference: <tip-f88731e3068f9d1392ba71cc9f50f035d26a0d4f@....kernel.org>
> Signed-off-by: H. Peter Anvin <hpa@...or.com>
> ---
>  arch/x86/include/asm/alternative.h |    7 ++++---
>  arch/x86/include/asm/cpufeature.h  |   10 ++++++----
>  2 files changed, 10 insertions(+), 7 deletions(-)

Hm, this patch is causing trouble in -tip testing again - it's triggering a 
colorful boot crash:

[    2.220002] calling  inet_init+0x0/0x23d @ 1
[    2.223343] NET: Registered protocol family 2
[    2.226727] IP route cache hash table entries: 32768 (order: 6, 262144 bytes)
[    2.233492] ------------[ cut here ]------------
[    2.236671] WARNING: at mm/vmalloc.c:107 vmap_page_range_noflush+0x309/0x3a0()
[    2.240001] Modules linked in:
...
[    3.090002] Kernel panic - not syncing: Failed to allocate TCP established hash table

So i've zapped them again. We really need to get to the bottom of this. Config 
and bootlog attached.

The crash looks very weird - and it's consistent with possible effects of some 
sort of code patching failure/mismatch.

It goes away if i revert these two:

 a3d2d12: x86, alternatives: correct obsolete use of "u8" in static_cpu_has()
 5dc71d4: x86, alternatives: Use 16-bit numbers for cpufeature index

I reproduced the crash twice before testing the revert.

Thanks,

	Ingo

View attachment "config-Tue_Jun_29_12_55_45_CEST_2010.bad" of type "text/plain" (71197 bytes)

View attachment "crash.log" of type "text/plain" (58055 bytes)