filemap-drop-the-mmap_sem-for-all-blocking-operations-v6

- added more comments as per Andrew's suggestion.
- fixed the fpin leaks in the two error paths that were pointed out.

Change-Id: I9933bc082581f0972aa6104ab1569ba1b25912a2
Link: http://lkml.kernel.org/r/20181212152757.10017-1-josef@toxicpanda.com


Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Rik van Riel <riel@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Git-Commit: 074eea6c5dae9a7ea26ec347607c4914b09a74b0
Git-Repo: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git


Signed-off-by: Vijayanand Jitta <vjitta@codeaurora.org>