f2fs: declare nested quota_sem and remove unnecessary sems

1.
f2fs_quota_sync
 -> down_read(&sbi->quota_sem)
 -> dquot_writeback_dquots
  -> f2fs_dquot_commit
   -> down_read(&sbi->quota_sem)

2.
f2fs_quota_sync
 -> down_read(&sbi->quota_sem)
  -> f2fs_write_data_pages
   -> f2fs_write_single_data_page
    -> down_write(&F2FS_I(inode)->i_sem)

f2fs_mkdir
 -> f2fs_do_add_link
   -> down_write(&F2FS_I(inode)->i_sem)
   -> f2fs_init_inode_metadata
    -> f2fs_new_node_page
     -> dquot_alloc_inode
      -> f2fs_dquot_mark_dquot_dirty
       -> down_read(&sbi->quota_sem)
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/super.c

@@ -2158,7 +2158,7 @@ static int f2fs_dquot_commit(struct dquot *dquot)
 	struct f2fs_sb_info *sbi = F2FS_SB(dquot->dq_sb);
 	int ret;
 
-	down_read(&sbi->quota_sem);
+	down_read_nested(&sbi->quota_sem, SINGLE_DEPTH_NESTING);
 	ret = dquot_commit(dquot);
 	if (ret < 0)
 		set_sbi_flag(sbi, SBI_QUOTA_NEED_REPAIR);
@@ -2182,13 +2182,10 @@ static int f2fs_dquot_acquire(struct dquot *dquot)
 static int f2fs_dquot_release(struct dquot *dquot)
 {
 	struct f2fs_sb_info *sbi = F2FS_SB(dquot->dq_sb);
-	int ret;
+	int ret = dquot_release(dquot);
 
-	down_read(&sbi->quota_sem);
-	ret = dquot_release(dquot);
 	if (ret < 0)
 		set_sbi_flag(sbi, SBI_QUOTA_NEED_REPAIR);
-	up_read(&sbi->quota_sem);
 	return ret;
 }
 
@@ -2196,29 +2193,22 @@ static int f2fs_dquot_mark_dquot_dirty(struct dquot *dquot)
 {
 	struct super_block *sb = dquot->dq_sb;
 	struct f2fs_sb_info *sbi = F2FS_SB(sb);
-	int ret;
-
-	down_read(&sbi->quota_sem);
-	ret = dquot_mark_dquot_dirty(dquot);
+	int ret = dquot_mark_dquot_dirty(dquot);
 
 	/* if we are using journalled quota */
 	if (is_journalled_quota(sbi))
 		set_sbi_flag(sbi, SBI_QUOTA_NEED_FLUSH);
 
-	up_read(&sbi->quota_sem);
 	return ret;
 }
 
 static int f2fs_dquot_commit_info(struct super_block *sb, int type)
 {
 	struct f2fs_sb_info *sbi = F2FS_SB(sb);
-	int ret;
+	int ret = dquot_commit_info(sb, type);
 
-	down_read(&sbi->quota_sem);
-	ret = dquot_commit_info(sb, type);
 	if (ret < 0)
 		set_sbi_flag(sbi, SBI_QUOTA_NEED_REPAIR);
-	up_read(&sbi->quota_sem);
 	return ret;
 }