aio: remove retry-based AIO

aio: remove retry-based AIO

This removes the retry-based AIO infrastructure now that nothing in tree
is using it.

We want to remove retry-based AIO because it is fundemantally unsafe.  It
retries IO submission from a kernel thread that has only assumed the mm of
the submitting task.  All other task_struct references in the IO
submission path will see the kernel thread, not the submitting task.  This
design flaw means that nothing of any meaningful complexity can use
retry-based AIO.

This removes all the code and data associated with the retry machinery.
The most significant benefit of this is the removal of the locking around
the unused run list in the submission path.

This has only been compiled.

Signed-off-by: Kent Overstreet <koverstreet@google.com>
Signed-off-by: Zach Brown <zab@redhat.com>
Cc: Zach Brown <zab@redhat.com>
Cc: Felipe Balbi <balbi@ti.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Mark Fasheh <mfasheh@suse.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Asai Thambi S P <asamymuthupa@micron.com>
Cc: Selvan Mani <smani@micron.com>
Cc: Sam Bradshaw <sbradshaw@micron.com>
Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>