BACKPORT: FROMGIT: userfaultfd/selftests: unify error handling

Introduce err()/_err() and replace all the different ways to fail the
program, mostly "fprintf" and "perror" with tons of exit() calls.  Always
stop the test program at any failure.

Link: https://lkml.kernel.org/r/20210412232753.1012412-6-peterx@redhat.com


Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Brian Geffon <bgeffon@google.com>
Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Joe Perches <joe@perches.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Lokesh Gidra <lokeshgidra@google.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Oliver Upton <oupton@google.com>
Cc: Shaohua Li <shli@fb.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Wang Qing <wangqing@vivo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
(cherry picked from commit fcd7d008016c9bc9bf134debfd077d59bba119d8
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git akpm)
Link: https://lore.kernel.org/patchwork/patch/1412454/



Conflicts: tools/testing/selftests/vm/userfaultfd.c
(Manual rebase)

Signed-off-by: Lokesh Gidra <lokeshgidra@google.com>
Bug: 187930641
Change-Id: Ic39dd286c3b1938752c3dc8c060a15b3d5db6564