Thread A wait for global F2FS_DIRTY_NODES decreased to zero,
it start a plug list, some requests have been added to this list.
Thread B lock one dirty node page, and wait this page write back.
But this page has been in plug list of thread A with PG_writeback flag.
Thread A keep on running and its plug list has no chance to finish,
so it seems a deadlock between cp and fsync path.
This patch add a wait on page write back before set node page dirty
to avoid this problem.
Signed-off-by: Yunlei He <heyunlei@huawei.com> Signed-off-by: Pengyang Hou <houpengyang@huawei.com> Reviewed-by: Chao Yu <yuchao0@huawei.com> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>