Man page 9 : mark_buffer_dirty

mark_buffer_dirty - mark a buffer_head as needing writeout

void mark_buffer_dirty(struct buffer_head *  bh );

bh
    the buffer_head to mark dirty

mark_buffer_dirty will set the dirty bit against the buffer, then set its backing page dirty, then tag the page as dirty in its address_spaceAqs radix tree and then attach the address_spaceAqs inode to its superblockAqs dirty inode list.

mark_buffer_dirty is atomic. It takes bh->b_page->mapping->private_lock, mapping->tree_lock and mapping->host->i_lock.