f2fs: implement a lock-free stat_show

The stat_show is just to show the current status of f2fs.
So, we can remove all the there-in locks.

Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>
diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
index 4024546..c3d5e36 100644
--- a/fs/f2fs/segment.h
+++ b/fs/f2fs/segment.h
@@ -380,26 +380,12 @@
 
 static inline block_t written_block_count(struct f2fs_sb_info *sbi)
 {
-	struct sit_info *sit_i = SIT_I(sbi);
-	block_t vblocks;
-
-	mutex_lock(&sit_i->sentry_lock);
-	vblocks = sit_i->written_valid_blocks;
-	mutex_unlock(&sit_i->sentry_lock);
-
-	return vblocks;
+	return SIT_I(sbi)->written_valid_blocks;
 }
 
 static inline unsigned int free_segments(struct f2fs_sb_info *sbi)
 {
-	struct free_segmap_info *free_i = FREE_I(sbi);
-	unsigned int free_segs;
-
-	read_lock(&free_i->segmap_lock);
-	free_segs = free_i->free_segments;
-	read_unlock(&free_i->segmap_lock);
-
-	return free_segs;
+	return FREE_I(sbi)->free_segments;
 }
 
 static inline int reserved_segments(struct f2fs_sb_info *sbi)
@@ -409,14 +395,7 @@
 
 static inline unsigned int free_sections(struct f2fs_sb_info *sbi)
 {
-	struct free_segmap_info *free_i = FREE_I(sbi);
-	unsigned int free_secs;
-
-	read_lock(&free_i->segmap_lock);
-	free_secs = free_i->free_sections;
-	read_unlock(&free_i->segmap_lock);
-
-	return free_secs;
+	return FREE_I(sbi)->free_sections;
 }
 
 static inline unsigned int prefree_segments(struct f2fs_sb_info *sbi)