proc 2/2: remove struct proc_dir_entry::owner

Setting ->owner as done currently (pde->owner = THIS_MODULE) is racy
as correctly noted at bug #12454. Someone can lookup entry with NULL
->owner, thus not pinning enything, and release it later resulting
in module refcount underflow.

We can keep ->owner and supply it at registration time like ->proc_fops
and ->data.

But this leaves ->owner as easy-manipulative field (just one C assignment)
and somebody will forget to unpin previous/pin current module when
switching ->owner. ->proc_fops is declared as "const" which should give
some thoughts.

->read_proc/->write_proc were just fixed to not require ->owner for
protection.

rmmod'ed directories will be empty and return "." and ".." -- no harm.
And directories with tricky enough readdir and lookup shouldn't be modular.
We definitely don't want such modular code.

Removing ->owner will also make PDE smaller.

So, let's nuke it.

Kudos to Jeff Layton for reminding about this, let's say, oversight.

http://bugzilla.kernel.org/show_bug.cgi?id=12454

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>

fs/proc/inode.c

@@ -58,11 +58,8 @@ static void proc_delete_inode(struct inode *inode)
 
 	/* Let go of any associated proc directory entry */
 	de = PROC_I(inode)->pde;
-	if (de) {
-		if (de->owner)
-			module_put(de->owner);
+	if (de)
 		de_put(de);
-	}
 	if (PROC_I(inode)->sysctl)
 		sysctl_head_put(PROC_I(inode)->sysctl);
 	clear_inode(inode);
@@ -449,12 +446,9 @@ struct inode *proc_get_inode(struct super_block *sb, unsigned int ino,
 {
 	struct inode * inode;
 
-	if (!try_module_get(de->owner))
-		goto out_mod;
-
 	inode = iget_locked(sb, ino);
 	if (!inode)
-		goto out_ino;
+		return NULL;
 	if (inode->i_state & I_NEW) {
 		inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
 		PROC_I(inode)->fd = 0;
@@ -485,16 +479,9 @@ struct inode *proc_get_inode(struct super_block *sb, unsigned int ino,
 			}
 		}
 		unlock_new_inode(inode);
-	} else {
-	       module_put(de->owner);
+	} else
 	       de_put(de);
-	}
 	return inode;
-
-out_ino:
-	module_put(de->owner);
-out_mod:
-	return NULL;
 }			
 
 int proc_fill_super(struct super_block *s)