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inetpeer: do not use zero refcnt for freed entries 

Followup of commit aa1039e73c (inetpeer: RCU conversion)

Unused inet_peer entries have a null refcnt.

Using atomic_inc_not_zero() in rcu lookups is not going to work for
them, and slow path is taken.

Fix this using -1 marker instead of 0 for deleted entries.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2010-06-15 21:47:39 -07:00 committed by David S. Miller
parent d5f31fbfd8
commit 5f2f892095
1 changed files with 8 additions and 2 deletions
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10
net/ipv4/inetpeer.c
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@ -187,7 +187,12 @@ static struct inet_peer *lookup_rcu_bh(__be32 daddr)
while (u != peer_avl_empty) {
if (daddr == u->v4daddr) {
if (unlikely(!atomic_inc_not_zero(&u->refcnt)))
/* Before taking a reference, check if this entry was
* deleted, unlink_from_pool() sets refcnt=-1 to make
* distinction between an unused entry (refcnt=0) and
* a freed one.
*/
if (unlikely(!atomic_add_unless(&u->refcnt, 1, -1)))
u = NULL;
return u;
}
@ -322,8 +327,9 @@ static void unlink_from_pool(struct inet_peer *p)
* in cleanup() function to prevent sudden disappearing. If we can
* atomically (because of lockless readers) take this last reference,
* it's safe to remove the node and free it later.
* We use refcnt=-1 to alert lockless readers this entry is deleted.
*/
if (atomic_cmpxchg(&p->refcnt, 1, 0) == 1) {
if (atomic_cmpxchg(&p->refcnt, 1, -1) == 1) {
struct inet_peer **stack[PEER_MAXDEPTH];
struct inet_peer ***stackptr, ***delp;
if (lookup(p->v4daddr, stack) != p)