proc: Clear the pieces of proc_inode that proc_evict_inode cares about

This just keeps everything tidier, and allows for using flags like
SLAB_TYPESAFE_BY_RCU where slabs are not always cleared before reuse.
I don't see reuse without reinitializing happening with the proc_inode
but I had a false alarm while reworking flushing of proc dentries and
indoes when a process dies that caused me to tidy this up.

The code is a little easier to follow and reason about this
way so I figured the changes might as well be kept.
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

fs/proc/inode.c

@@ -33,21 +33,27 @@ static void proc_evict_inode(struct inode *inode)
 {
 	struct proc_dir_entry *de;
 	struct ctl_table_header *head;
+	struct proc_inode *ei = PROC_I(inode);
 
 	truncate_inode_pages_final(&inode->i_data);
 	clear_inode(inode);
 
 	/* Stop tracking associated processes */
-	put_pid(PROC_I(inode)->pid);
+	if (ei->pid) {
+		put_pid(ei->pid);
+		ei->pid = NULL;
+	}
 
 	/* Let go of any associated proc directory entry */
-	de = PDE(inode);
-	if (de)
+	de = ei->pde;
+	if (de) {
 		pde_put(de);
+		ei->pde = NULL;
+	}
 
-	head = PROC_I(inode)->sysctl;
+	head = ei->sysctl;
 	if (head) {
-		RCU_INIT_POINTER(PROC_I(inode)->sysctl, NULL);
+		RCU_INIT_POINTER(ei->sysctl, NULL);
 		proc_sys_evict_inode(inode, head);
 	}
 }