Code:  static void dump_completed_IO(struct inode * inode)
 {
 #ifdef	EXT4_DEBUG
 	struct list_head *cur, *before, *after;
 	ext4_io_end_t *io, *io0, *io1;
 
 	if (list_empty(&EXT4_I(inode)->i_completed_io_list)){
 		ext4_debug("inode %lu completed_io list is empty\n", inode->i_ino);
 		return;
 	}
 
 	ext4_debug("Dump inode %lu completed_io list \n", inode->i_ino);
 	list_for_each_entry(io, &EXT4_I(inode)->i_completed_io_list, list){
 		cur = &io->list;
 		before = cur->prev;
		io0 = container_of(before, ext4_io_end_t, list);
		after = cur->next;
		io1 = container_of(after, ext4_io_end_t, list);

 		ext4_debug("io 0x%p from inode %lu,prev 0x%p,next 0x%p\n",
 			    io, inode->i_ino, io0, io1);
 	}
 #endif
 }

Commit Message: ext4: use ext4_get_block_write in buffer write

Allocate uninitialized extent before ext4 buffer write and
convert the extent to initialized after io completes.
The purpose is to make sure an extent can only be marked
initialized after it has been written with new data so
we can safely drop the i_mutex lock in ext4 DIO read without
exposing stale data. This helps to improve multi-thread DIO
read performance on high-speed disks.

Skip the nobh and data=journal mount cases to make things simple for now.

Signed-off-by: Jiaying Zhang <jiayingz@google.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
CWE ID: 
 static void dump_completed_IO(struct inode * inode)
 {
 #ifdef	EXT4_DEBUG
 	struct list_head *cur, *before, *after;
 	ext4_io_end_t *io, *io0, *io1;
	unsigned long flags;
 
 	if (list_empty(&EXT4_I(inode)->i_completed_io_list)){
 		ext4_debug("inode %lu completed_io list is empty\n", inode->i_ino);
 		return;
 	}
 
 	ext4_debug("Dump inode %lu completed_io list \n", inode->i_ino);
	spin_lock_irqsave(&EXT4_I(inode)->i_completed_io_lock, flags);
 	list_for_each_entry(io, &EXT4_I(inode)->i_completed_io_list, list){
 		cur = &io->list;
 		before = cur->prev;
		io0 = container_of(before, ext4_io_end_t, list);
		after = cur->next;
		io1 = container_of(after, ext4_io_end_t, list);

 		ext4_debug("io 0x%p from inode %lu,prev 0x%p,next 0x%p\n",
 			    io, inode->i_ino, io0, io1);
 	}
	spin_unlock_irqrestore(&EXT4_I(inode)->i_completed_io_lock, flags);
 #endif
 }
