2.6.13: More on drivers/block/loop.c

[Ian Collier <Ian.Collier@comlab.ox.ac.uk>]

Vanilla 2.6.13 doesn't crash.

However, unpack a fresh copy of 2.6.13, edit include/linux/loop.h to
change LO_KEY_SIZE from 32 to 1844, and *boom*.  [Don't ask me why
1844... that's just what PPDD wants.]

It's crashing somewhere in loop_set_status_old, probably during the
call to copy_from_user, but the crash messages aren't that helpful as
they are different each time, often seem to happen during an interrupt,
and usually contain pages of recursive calls to do_page_fault and
error_code.

The loop_set_status_old function has two local variables, each of which
is now 1812 bytes longer than it was, and I'm wondering if it's a stack
overflow problem.  How much stack is a kernel function allowed to use,
anyway?

Replacing these variables with kmalloc'd pointers seems to stop the crashes
anyway, so I'll pass that tip on to the PPDD folks.

imc