ext4: fast commit may miss tracking unwritten range during ftruncate

If use FALLOC_FL_KEEP_SIZE to alloc unwritten range at bottom, the
inode->i_size will not include the unwritten range. When call
ftruncate with fast commit enabled, it will miss to track the
unwritten range.

Change to trace the full range during ftruncate.

Signed-off-by: Xin Yin <yinxin.x@bytedance.com>
Reviewed-by: Harshad Shirwadkar <harshadshirwadkar@gmail.com>
Link: https://lore.kernel.org/r/20211223032337.5198-3-yinxin.x@bytedance.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org