Repeated corruption of file->f_ep_lock

[Paul Mackerras]

David Woodhouse writes:

> The previous and next members of 'struct file', which are f_ep_list and
> f_mapping respectively, are always fine. It's just f_ep_lock which is
> scribbled upon, and the scribble is fairly repeatable: 'owner_cpu' is
> almost always set to 0x901 but occasionally 0x501, and the 'lock' field
> has values like 20282484, 24042884, 28022484, 24042084, 22000424 (hex).
> Do those numbers seem meaningful to anyone? Any clues as to where they
> might be coming from?

They look like part of an exception stack frame.  The 901 or 501 would
be the trap number; 500 for an external interrupt or 900 for a
decrementer interrupt, plus 1 which we use as a marker to say that
only the volatile registers have been saved in the frame.  The other
values (20282484 etc.) could possibly be condition register values.
That would fit with owner_cpu being 2 words past the lock field; the
trap field in struct pt_regs is 2 words past the ccr field.

Paul.