Re: 2.6.21-rc5-mm[12]: Oops on bootup in xor_see_2

On Saturday March 31, akpm@xxxxxxxxxxxxxxxxxxxx wrote:
On Sat, 31 Mar 2007 17:36:47 +0000 Bernhard Rosenkraenzer <bero@xxxxxxxxxxxx> wrote:

I'm getting this Oops when booting an 2.6.21-rc5-mm1 or 2.6.21-rc5-mm2 on an
Acer Aspire 1501 LMi in 32 bit mode (2.6.21-rc4-mm1 + hotfixes works
perfectly):

xor: automatically using best checksumming function: pIII_sse

Hmmm... I've seen that before

Code: 44 89 74 24 48 0f 20 c6 0f 06 0f 11 04 24 0f 11 4c 24 10 0f 11 54 24 20
0f
11 5c 24 30 0f 18 82 00 01 00 00 0f 18 82 20 01 00 00 <00> 00 00 00 00
00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
-

Them bytes that look like '00' are mostly supposed to look like 'F0' -
an x86 'noop'.

Apparently a bin-utils bug. An alpha of OpenSUSE-10.3 was compiling
kernels like this. I'm told it has been fixed.

What distro/gcc version/binutils version was this compiled on?

It is possible that we should change the ".align 32" in
include/asm-i386/xor.h to ".align 32, 0xf0" or similar, but my
assembler knowledge stopped growing when it reached 6809, so I'd
rather someone who knew something about it did anything that was
required....


Dan, I'm assuming your changes in there are the cause of this. AFAICT all
you're doing is moving code around, so it's a bit odd.

Bernhard, the config would be useful please.

Neil, is calibrate_xor_block() being rational?

b1 = (void *) __get_free_pages(GFP_KERNEL, 2);
...
b2 = b1 + 2*PAGE_SIZE + BENCH_SIZE;

Is it correct to add BENCH_SIZE to b2 here?

I think it is intentional. I cannot say if it is correct.
The purpose is to defeat cache effects somehow.
The result of that code together with the value of BENCH_SIZE being
PAGE_SIZE is that 4 pages are allocated, and the first and last are
used.
I have no idea how any cache would treat this, but that seems to be
the intent of the code.

NeilBrown
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