BugLink: http://bugs.launchpad.net/bugs/1673538

commit eb5efbcb upstream.

The write_end() function must always unlock the page and drop its ref
count, even on an error.
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>