This patch tries to fix the problem of page fault exception
caused by accessing nmiaction structure in nmi if kmemcheck
is enabled.

If kmemcheck is enabled, the memory allocated through slab are
in pages that are marked non-present, so that some checks could
be done in the page fault handling code ( e.g. whether the
memory is read before written to ).

As nmiaction is allocated in this way, so it resides in a
non-present page. Then there is a page fault while the nmi code
accessing the nmiaction structure, which would then cause a
warning by WARN_ON_ONCE(in_nmi()) in kmemcheck_fault(), called
by do_page_fault().

This significantly simplifies the code as well, as the whole
dynamic allocation dance goes away.

v2: as Peter suggested, changed the nmiaction to use static
    storage.

v3: as Peter suggested, use macro to shorten the codes. Also
    keep the original usage of register_nmi_handler, so users of
    this call doesn't need change.

Tested-by: Seiji Aguchi <seiji.aguchi@hds.com>
Fixes: https://lkml.org/lkml/2012/3/2/356


Signed-off-by: Li Zhong <zhong@linux.vnet.ibm.com>
[ simplified the wrappers ]
Signed-off-by: Don Zickus <dzickus@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: thomas.mingarelli@hp.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/1333051877-15755-4-git-send-email-dzickus@redhat.com


[ tidied the patch a bit ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>