mark_buffer_dirty — mark a buffer_head as needing writeout
void fastcall mark_buffer_dirty (struct buffer_head * bh);
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_space's radix
tree and then attach the address_space's inode to its superblock's dirty
inode list.
mark_buffer_dirty is atomic. It takes bh->b_page->mapping->private_lock,
mapping->tree_lock and the global inode_lock.