dynamic fsync: add kernel panic notifier to force flush outstanding data

more paranoia safety checks

Signed-off-by: Paul Reioux <reioux@gmail.com>
Signed-off-by: umberto1978 <ur.tecnotop@gmail.com>
dynamic fsync: favor true case since most will be using this feature

Signed-off-by: Paul Reioux <reioux@gmail.com>
Signed-off-by: umberto1978 <ur.tecnotop@gmail.com>