Re: Silent corruption on AMD64

[Aaron Lehmann <aaronl@vitelus.com>]

On Sat, Mar 31, 2007 at 07:52:36PM -0700, Andrew Morton wrote:
> Are you able to provide us with some before-and-after data so we
> can see this corruption.
> 
> See, if it's dropped-bits or shifted-data or eight-byte-aligned
> kernel addresses or whatever, that helps us generate theories..

Sure.

I created a large file containing the repeating ASCII string "abcdefgh",
and subjected it to the corruption I described earlier. The correct
hex sequence is:

61 62 63 64 65 66 67 68

Here were some of the permutations that I found in corrupted copies:

61 62 63 64 92 57 5C 0A
61 62 63 64 A2 2D E1 C7
61 62 63 64 11 38 0E B6
61 62 63 64 57 B1 EE 1F
61 62 63 64 E0 3D 10 21
61 62 63 64 97 E1 C0 F5

I did not observe any errors other than replacements of four-byte
blocks. These errors always started at addresses in the file that had
a remainder of 12 modulo 16 (i.e. the hex addresses always ended in
'C'). There was an average about one error per 300MB.