inetpeer: reduce stack usage

On 64bit arches, we use 752 bytes of stack when cleanup_once() is called
from inet_getpeer().

Lets share the avl stack to save ~376 bytes.

Before patch :

# objdump -d net/ipv4/inetpeer.o | scripts/checkstack.pl

0x000006c3 unlink_from_pool [inetpeer.o]: 376
0x00000721 unlink_from_pool [inetpeer.o]: 376
0x00000cb1 inet_getpeer [inetpeer.o]: 376
0x00000e6d inet_getpeer [inetpeer.o]: 376
0x0004 inet_initpeers [inetpeer.o]: 112
# size net/ipv4/inetpeer.o
text data bss dec hex filename
5320 432 21 5773 168d net/ipv4/inetpeer.o

After patch :

objdump -d net/ipv4/inetpeer.o | scripts/checkstack.pl
0x00000c11 inet_getpeer [inetpeer.o]: 376
0x00000dcd inet_getpeer [inetpeer.o]: 376
0x00000ab9 peer_check_expire [inetpeer.o]: 328
0x00000b7f peer_check_expire [inetpeer.o]: 328
0x0004 inet_initpeers [inetpeer.o]: 112
# size net/ipv4/inetpeer.o
text data bss dec hex filename
5163 432 21 5616 15f0 net/ipv4/inetpeer.o

Signed-off-by: Eric Dumazet <[e-mail]>
Cc: Scot Doyle <[e-mail]>
Cc: Stephen Hemminger <[e-mail]>
Cc: Hiroaki SHIMODA <[e-mail]>
Reviewed-by: Hiroaki SHIMODA <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/ipv4/inetpeer.c

···
 }
 
 /* May be called with local BH enabled. */
-static void unlink_from_pool(struct inet_peer *p, struct inet_peer_base *base)
+static void unlink_from_pool(struct inet_peer *p, struct inet_peer_base *base,
+			     struct inet_peer __rcu **stack[PEER_MAXDEPTH])
 {
 	int do_free;
 
···
 	 * We use refcnt=-1 to alert lockless readers this entry is deleted.
 	 */
 	if (atomic_cmpxchg(&p->refcnt, 1, -1) == 1) {
-		struct inet_peer __rcu **stack[PEER_MAXDEPTH];
 		struct inet_peer __rcu ***stackptr, ***delp;
 		if (lookup(&p->daddr, stack, base) != p)
 			BUG();
···
 }
 
 /* May be called with local BH enabled. */
-static int cleanup_once(unsigned long ttl)
+static int cleanup_once(unsigned long ttl, struct inet_peer __rcu **stack[PEER_MAXDEPTH])
 {
 	struct inet_peer *p = NULL;
 
···
 		 * happen because of entry limits in route cache. */
 		return -1;
 
-	unlink_from_pool(p, peer_to_base(p));
+	unlink_from_pool(p, peer_to_base(p), stack);
 	return 0;
 }
 
···
 
 	if (base->total >= inet_peer_threshold)
 		/* Remove one less-recently-used entry. */
-		cleanup_once(0);
+		cleanup_once(0, stack);
 
 	return p;
 }
···
 {
 	unsigned long now = jiffies;
 	int ttl, total;
+	struct inet_peer __rcu **stack[PEER_MAXDEPTH];
 
 	total = compute_total();
 	if (total >= inet_peer_threshold)
···
 		ttl = inet_peer_maxttl
 				- (inet_peer_maxttl - inet_peer_minttl) / HZ *
 					total / inet_peer_threshold * HZ;
-	while (!cleanup_once(ttl)) {
+	while (!cleanup_once(ttl, stack)) {
 		if (jiffies != now)
 			break;
 	}