In f2fs_do_write_data_page, when the data block is NULL_ADDR, it skips
writepage considering that it has been already truncated.
This results in an infinite loop as the PAGECACHE_TAG_TOWRITE tag is not
cleared during the writeback process for a compressed file including
NULL_ADDR in compress_mode=user.
This is the reproduction process:
1. dd if=/dev/zero bs=4096 count=1024 seek=1024 of=testfile
2. f2fs_io compress testfile
3. dd if=/dev/zero bs=4096 count=1 conv=notrunc of=testfile
4. f2fs_io decompress testfile
To prevent the problem, let's check whether the cluster is fully
allocated before redirty its pages.
Fixes: 5fdb322ff2c2 ("f2fs: add F2FS_IOC_DECOMPRESS_FILE and F2FS_IOC_COMPRESS_FILE")
Reviewed-by: Sungjong Seo <sj1557.seo@xxxxxxxxxxx>
Reviewed-by: Sunmin Jeong <s_min.jeong@xxxxxxxxxxx>
Tested-by: Jaewook Kim <jw5454.kim@xxxxxxxxxxx>
Signed-off-by: Yeongjin Gil <youngjin.gil@xxxxxxxxxxx>