cache aliasing in dup_mmap

[Russell King - ARM Linux]

On Mon, Nov 16, 2009 at 12:23:36PM -0500, Steven Walter wrote:
> Yes, SIGSEGV after 88 boots, with a crash that we previously
> identified as caused by this cache corruption issue.  Attached are the
> patches I used, as manually backported to 2.6.18.5.  Stock 2.6.18.5
> would reliably crash in under 1000 reboots, whereas  with my ad-hoc
> fix (also attached) we were able to run 8000 reboots before we ended
> the test.

I can see no reason for the difference between the two.  The backport
looks fine.

The only difference I can see is:

- version which works

> diff --git a/src/mm/memory.c b/src/mm/memory.c
> index 0b7a668..d0bc8c1 100644

- version which doesn't

> diff --git a/src/mm/memory.c b/src/mm/memory.c
> index f508c60..69d8d32 100644

That first index number gives the sha1 hash of the git object storing
this file.  Since they're different, these two patches weren't applied
to the same file.

Could there be other changes in your tree which could be affecting the
behaviour in this area?