The atomic/volatile operation should be done in pair of start and commit
ioctl.
For example, if a killed process remains open-ended atomic operation, we should
drop its flag as well as its atomic data. Otherwise, if sqlite initiates another
operation which doesn't require atomic writes, it will lose every data, since
f2fs still treats with them as atomic writes; nobody will trigger its commit.

Reported-by: Miao Xie <miaoxie@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>