If a fault in the kernel leads to an unexpected protection fault whilst in
a code path which holds mmap_sem we will deadlock in do_page_fault() while
trying to classify the fault.  By carefully testing the source of the fault
we can detect and OOPS on the vast majority of these, greatly enhancing
diagnosis of such bugs.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>