f2fs: fix to account FS_CP_DATA_IO correctly

f2fs_inode_info.cp_task was introduced for FS_CP_DATA_IO accounting
since commit b0af6d49 ("f2fs: add app/fs io stat").

However, cp_task usage coverage has been increased due to below
commits:
commit 040d2bb3 ("f2fs: fix to avoid deadloop if data_flush is on")
commit 186857c5 ("f2fs: fix potential recursive call when enabling data_flush")

So that, if data_flush mountoption is on, when data flush was
triggered from background, the IO from data flush will be accounted
as checkpoint IO type incorrectly.

In order to fix this issue, this patch splits cp_task into two:
a) cp_task: used for IO accounting
b) wb_task: used to avoid deadlock

Fixes: 040d2bb3 ("f2fs: fix to avoid deadloop if data_flush is on")
Fixes: 186857c5 ("f2fs: fix potential recursive call when enabling data_flush")
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/checkpoint.c

@@ -1061,7 +1061,8 @@ void f2fs_remove_dirty_inode(struct inode *inode)
 	spin_unlock(&sbi->inode_lock[type]);
 }
 
-int f2fs_sync_dirty_inodes(struct f2fs_sb_info *sbi, enum inode_type type)
+int f2fs_sync_dirty_inodes(struct f2fs_sb_info *sbi, enum inode_type type,
+						bool from_cp)
 {
 	struct list_head *head;
 	struct inode *inode;
@@ -1096,11 +1097,15 @@ int f2fs_sync_dirty_inodes(struct f2fs_sb_info *sbi, enum inode_type type)
 	if (inode) {
 		unsigned long cur_ino = inode->i_ino;
 
-		F2FS_I(inode)->cp_task = current;
+		if (from_cp)
+			F2FS_I(inode)->cp_task = current;
+		F2FS_I(inode)->wb_task = current;
 
 		filemap_fdatawrite(inode->i_mapping);
 
-		F2FS_I(inode)->cp_task = NULL;
+		F2FS_I(inode)->wb_task = NULL;
+		if (from_cp)
+			F2FS_I(inode)->cp_task = NULL;
 
 		iput(inode);
 		/* We need to give cpu to another writers. */
@@ -1229,7 +1234,7 @@ static int block_operations(struct f2fs_sb_info *sbi)
 	/* write all the dirty dentry pages */
 	if (get_pages(sbi, F2FS_DIRTY_DENTS)) {
 		f2fs_unlock_all(sbi);
-		err = f2fs_sync_dirty_inodes(sbi, DIR_INODE);
+		err = f2fs_sync_dirty_inodes(sbi, DIR_INODE, true);
 		if (err)
 			return err;
 		cond_resched();

fs/f2fs/data.c

@@ -2856,7 +2856,7 @@ int f2fs_write_single_data_page(struct page *page, int *submitted,
 	}
 	unlock_page(page);
 	if (!S_ISDIR(inode->i_mode) && !IS_NOQUOTA(inode) &&
-			!F2FS_I(inode)->cp_task && allow_balance)
+			!F2FS_I(inode)->wb_task && allow_balance)
 		f2fs_balance_fs(sbi, need_balance_fs);
 
 	if (unlikely(f2fs_cp_error(sbi))) {
@@ -3156,7 +3156,7 @@ static inline bool __should_serialize_io(struct inode *inode,
 					struct writeback_control *wbc)
 {
 	/* to avoid deadlock in path of data flush */
-	if (F2FS_I(inode)->cp_task)
+	if (F2FS_I(inode)->wb_task)
 		return false;
 
 	if (!S_ISREG(inode->i_mode))

fs/f2fs/f2fs.h

@@ -786,6 +786,7 @@ struct f2fs_inode_info {
 	unsigned int clevel;		/* maximum level of given file name */
 	struct task_struct *task;	/* lookup and create consistency */
 	struct task_struct *cp_task;	/* separate cp/wb IO stats*/
+	struct task_struct *wb_task;	/* indicate inode is in context of writeback */
 	nid_t i_xattr_nid;		/* node id that contains xattrs */
 	loff_t	last_disk_size;		/* lastly written file size */
 	spinlock_t i_size_lock;		/* protect last_disk_size */
@@ -3745,7 +3746,8 @@ int f2fs_recover_orphan_inodes(struct f2fs_sb_info *sbi);
 int f2fs_get_valid_checkpoint(struct f2fs_sb_info *sbi);
 void f2fs_update_dirty_folio(struct inode *inode, struct folio *folio);
 void f2fs_remove_dirty_inode(struct inode *inode);
-int f2fs_sync_dirty_inodes(struct f2fs_sb_info *sbi, enum inode_type type);
+int f2fs_sync_dirty_inodes(struct f2fs_sb_info *sbi, enum inode_type type,
+								bool from_cp);
 void f2fs_wait_on_all_pages(struct f2fs_sb_info *sbi, int type);
 u64 f2fs_get_sectors_written(struct f2fs_sb_info *sbi);
 int f2fs_write_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc);

fs/f2fs/segment.c

@@ -476,7 +476,7 @@ void f2fs_balance_fs_bg(struct f2fs_sb_info *sbi, bool from_bg)
 		mutex_lock(&sbi->flush_lock);
 
 		blk_start_plug(&plug);
-		f2fs_sync_dirty_inodes(sbi, FILE_INODE);
+		f2fs_sync_dirty_inodes(sbi, FILE_INODE, false);
 		blk_finish_plug(&plug);
 
 		mutex_unlock(&sbi->flush_lock);