dm mirror log: clear log bits up to BITS_PER_LONG boundary

commit 90736eb3 upstream.

Commit 85e123c2 ("dm mirror log: round up region bitmap size to
BITS_PER_LONG") introduced a regression on 64-bit architectures in the
lvm testsuite tests: lvcreate-mirror, mirror-names and vgsplit-operation.

If the device is shrunk, we need to clear log bits beyond the end of the
device. The code clears bits up to a 32-bit boundary and then calculates
lc->sync_count by summing set bits up to a 64-bit boundary (the commit
changed that; previously, this boundary was 32-bit too). So, it was using
some non-zeroed bits in the calculation and this caused misbehavior.

Fix this regression by clearing bits up to BITS_PER_LONG boundary.

Fixes: 85e123c2

 ("dm mirror log: round up region bitmap size to BITS_PER_LONG")
Cc: stable@vger.kernel.org
Reported-by: Benjamin Marzinski <bmarzins@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>