Re: [PATCH] mm: fix page_mkclean_one

[Russell King <rmk+lkml@arm.linux.org.uk>]

On Wed, Dec 27, 2006 at 10:20:20PM -0700, Gordon Farquharson wrote:
> I have run the program a few times, and the output is pretty
> consistent. However, when I increase the target size, the difference
> between the expected and actual values is larger.
> 
> Written as (749)935(738)
> Chunk 1113 corrupted (1-1455)  (2965-323)
> Expected 89, got 93

This is not the corruption Linus is after.  Note that the corruption starts
at offset '1'.  Also note that:

89 = 1113 & 255
93 = 1113 & 255 | (1113 >> 8)

and if you look at glibc's memset() function, you'll notice that's exactly
what you expect if you pass a non-8bit value to it.  Ergo, what you're
seeing is utterly expected given glibc's memset() implementation on ARM.

Fixing Linus' test program to pass nr & 255 to memset results in clean
passes on 2.6.9 on TheCus N2100 (IOP8032x) and 2.6.16.9 StrongARM
machines (as would be expected.)

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
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