f2fs: fix to overcome inline_data floods

The scenario is:
1. create lots of node blocks
2. sync
3. write lots of inline_data
-> got panic due to no free space

In that case, we should flush node blocks when writing inline_data in #3,
and trigger gc as well.
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/gc.c

@@ -838,8 +838,15 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync)
 
 	if (gc_type == BG_GC && has_not_enough_free_secs(sbi, sec_freed)) {
 		gc_type = FG_GC;
+		/*
+		 * If there is no victim and no prefree segment but still not
+		 * enough free sections, we should flush dent/node blocks and do
+		 * garbage collections.
+		 */
 		if (__get_victim(sbi, &segno, gc_type) || prefree_segments(sbi))
 			write_checkpoint(sbi, &cpc);
+		else if (has_not_enough_free_secs(sbi, 0))
+			write_checkpoint(sbi, &cpc);
 	}
 
 	if (segno == NULL_SEGNO && !__get_victim(sbi, &segno, gc_type))