forked from Minki/linux
98158f5a85
Instead of directly accessing "peer", change to code to operate using a "struct inet_peer_base *" pointer. This will facilitate the addition of a seperate tree for ipv6 peer entries. Signed-off-by: David S. Miller <davem@davemloft.net>
552 lines
17 KiB
C
552 lines
17 KiB
C
/*
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* INETPEER - A storage for permanent information about peers
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*
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* This source is covered by the GNU GPL, the same as all kernel sources.
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*
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* Authors: Andrey V. Savochkin <saw@msu.ru>
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*/
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#include <linux/module.h>
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#include <linux/types.h>
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#include <linux/slab.h>
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#include <linux/interrupt.h>
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#include <linux/spinlock.h>
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#include <linux/random.h>
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#include <linux/timer.h>
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#include <linux/time.h>
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#include <linux/kernel.h>
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#include <linux/mm.h>
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#include <linux/net.h>
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#include <net/ip.h>
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#include <net/inetpeer.h>
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/*
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* Theory of operations.
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* We keep one entry for each peer IP address. The nodes contains long-living
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* information about the peer which doesn't depend on routes.
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* At this moment this information consists only of ID field for the next
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* outgoing IP packet. This field is incremented with each packet as encoded
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* in inet_getid() function (include/net/inetpeer.h).
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* At the moment of writing this notes identifier of IP packets is generated
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* to be unpredictable using this code only for packets subjected
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* (actually or potentially) to defragmentation. I.e. DF packets less than
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* PMTU in size uses a constant ID and do not use this code (see
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* ip_select_ident() in include/net/ip.h).
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*
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* Route cache entries hold references to our nodes.
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* New cache entries get references via lookup by destination IP address in
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* the avl tree. The reference is grabbed only when it's needed i.e. only
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* when we try to output IP packet which needs an unpredictable ID (see
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* __ip_select_ident() in net/ipv4/route.c).
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* Nodes are removed only when reference counter goes to 0.
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* When it's happened the node may be removed when a sufficient amount of
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* time has been passed since its last use. The less-recently-used entry can
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* also be removed if the pool is overloaded i.e. if the total amount of
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* entries is greater-or-equal than the threshold.
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*
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* Node pool is organised as an AVL tree.
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* Such an implementation has been chosen not just for fun. It's a way to
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* prevent easy and efficient DoS attacks by creating hash collisions. A huge
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* amount of long living nodes in a single hash slot would significantly delay
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* lookups performed with disabled BHs.
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*
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* Serialisation issues.
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* 1. Nodes may appear in the tree only with the pool lock held.
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* 2. Nodes may disappear from the tree only with the pool lock held
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* AND reference count being 0.
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* 3. Nodes appears and disappears from unused node list only under
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* "inet_peer_unused_lock".
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* 4. Global variable peer_total is modified under the pool lock.
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* 5. struct inet_peer fields modification:
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* avl_left, avl_right, avl_parent, avl_height: pool lock
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* unused: unused node list lock
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* refcnt: atomically against modifications on other CPU;
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* usually under some other lock to prevent node disappearing
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* dtime: unused node list lock
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* v4daddr: unchangeable
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* ip_id_count: atomic value (no lock needed)
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*/
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static struct kmem_cache *peer_cachep __read_mostly;
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#define node_height(x) x->avl_height
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#define peer_avl_empty ((struct inet_peer *)&peer_fake_node)
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#define peer_avl_empty_rcu ((struct inet_peer __rcu __force *)&peer_fake_node)
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static const struct inet_peer peer_fake_node = {
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.avl_left = peer_avl_empty_rcu,
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.avl_right = peer_avl_empty_rcu,
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.avl_height = 0
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};
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static struct inet_peer_base {
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struct inet_peer __rcu *root;
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spinlock_t lock;
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int total;
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} v4_peers = {
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.root = peer_avl_empty_rcu,
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.lock = __SPIN_LOCK_UNLOCKED(v4_peers.lock),
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.total = 0,
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};
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#define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */
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/* Exported for sysctl_net_ipv4. */
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int inet_peer_threshold __read_mostly = 65536 + 128; /* start to throw entries more
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* aggressively at this stage */
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int inet_peer_minttl __read_mostly = 120 * HZ; /* TTL under high load: 120 sec */
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int inet_peer_maxttl __read_mostly = 10 * 60 * HZ; /* usual time to live: 10 min */
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int inet_peer_gc_mintime __read_mostly = 10 * HZ;
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int inet_peer_gc_maxtime __read_mostly = 120 * HZ;
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static struct {
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struct list_head list;
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spinlock_t lock;
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} unused_peers = {
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.list = LIST_HEAD_INIT(unused_peers.list),
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.lock = __SPIN_LOCK_UNLOCKED(unused_peers.lock),
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};
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static void peer_check_expire(unsigned long dummy);
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static DEFINE_TIMER(peer_periodic_timer, peer_check_expire, 0, 0);
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/* Called from ip_output.c:ip_init */
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void __init inet_initpeers(void)
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{
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struct sysinfo si;
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/* Use the straight interface to information about memory. */
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si_meminfo(&si);
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/* The values below were suggested by Alexey Kuznetsov
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* <kuznet@ms2.inr.ac.ru>. I don't have any opinion about the values
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* myself. --SAW
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*/
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if (si.totalram <= (32768*1024)/PAGE_SIZE)
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inet_peer_threshold >>= 1; /* max pool size about 1MB on IA32 */
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if (si.totalram <= (16384*1024)/PAGE_SIZE)
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inet_peer_threshold >>= 1; /* about 512KB */
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if (si.totalram <= (8192*1024)/PAGE_SIZE)
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inet_peer_threshold >>= 2; /* about 128KB */
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peer_cachep = kmem_cache_create("inet_peer_cache",
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sizeof(struct inet_peer),
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0, SLAB_HWCACHE_ALIGN | SLAB_PANIC,
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NULL);
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/* All the timers, started at system startup tend
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to synchronize. Perturb it a bit.
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*/
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peer_periodic_timer.expires = jiffies
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+ net_random() % inet_peer_gc_maxtime
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+ inet_peer_gc_maxtime;
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add_timer(&peer_periodic_timer);
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}
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/* Called with or without local BH being disabled. */
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static void unlink_from_unused(struct inet_peer *p)
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{
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if (!list_empty(&p->unused)) {
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spin_lock_bh(&unused_peers.lock);
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list_del_init(&p->unused);
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spin_unlock_bh(&unused_peers.lock);
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}
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}
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/*
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* Called with local BH disabled and the pool lock held.
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*/
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#define lookup(_daddr, _stack, _base) \
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({ \
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struct inet_peer *u; \
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struct inet_peer __rcu **v; \
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\
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stackptr = _stack; \
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*stackptr++ = &_base->root; \
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for (u = rcu_dereference_protected(_base->root, \
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lockdep_is_held(&_base->lock)); \
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u != peer_avl_empty; ) { \
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if (_daddr == u->v4daddr) \
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break; \
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if ((__force __u32)_daddr < (__force __u32)u->v4daddr) \
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v = &u->avl_left; \
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else \
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v = &u->avl_right; \
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*stackptr++ = v; \
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u = rcu_dereference_protected(*v, \
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lockdep_is_held(&_base->lock)); \
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} \
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u; \
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})
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/*
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* Called with rcu_read_lock_bh()
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* Because we hold no lock against a writer, its quite possible we fall
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* in an endless loop.
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* But every pointer we follow is guaranteed to be valid thanks to RCU.
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* We exit from this function if number of links exceeds PEER_MAXDEPTH
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*/
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static struct inet_peer *lookup_rcu_bh(__be32 daddr, struct inet_peer_base *base)
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{
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struct inet_peer *u = rcu_dereference_bh(base->root);
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int count = 0;
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while (u != peer_avl_empty) {
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if (daddr == u->v4daddr) {
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/* Before taking a reference, check if this entry was
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* deleted, unlink_from_pool() sets refcnt=-1 to make
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* distinction between an unused entry (refcnt=0) and
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* a freed one.
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*/
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if (unlikely(!atomic_add_unless(&u->refcnt, 1, -1)))
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u = NULL;
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return u;
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}
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if ((__force __u32)daddr < (__force __u32)u->v4daddr)
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u = rcu_dereference_bh(u->avl_left);
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else
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u = rcu_dereference_bh(u->avl_right);
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if (unlikely(++count == PEER_MAXDEPTH))
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break;
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}
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return NULL;
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}
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/* Called with local BH disabled and the pool lock held. */
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#define lookup_rightempty(start, base) \
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({ \
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struct inet_peer *u; \
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struct inet_peer __rcu **v; \
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*stackptr++ = &start->avl_left; \
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v = &start->avl_left; \
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for (u = rcu_dereference_protected(*v, \
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lockdep_is_held(&base->lock)); \
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u->avl_right != peer_avl_empty_rcu; ) { \
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v = &u->avl_right; \
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*stackptr++ = v; \
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u = rcu_dereference_protected(*v, \
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lockdep_is_held(&base->lock)); \
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} \
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u; \
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})
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/* Called with local BH disabled and the pool lock held.
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* Variable names are the proof of operation correctness.
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* Look into mm/map_avl.c for more detail description of the ideas.
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*/
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static void peer_avl_rebalance(struct inet_peer __rcu **stack[],
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struct inet_peer __rcu ***stackend,
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struct inet_peer_base *base)
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{
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struct inet_peer __rcu **nodep;
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struct inet_peer *node, *l, *r;
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int lh, rh;
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while (stackend > stack) {
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nodep = *--stackend;
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node = rcu_dereference_protected(*nodep,
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lockdep_is_held(&base->lock));
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l = rcu_dereference_protected(node->avl_left,
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lockdep_is_held(&base->lock));
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r = rcu_dereference_protected(node->avl_right,
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lockdep_is_held(&base->lock));
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lh = node_height(l);
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rh = node_height(r);
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if (lh > rh + 1) { /* l: RH+2 */
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struct inet_peer *ll, *lr, *lrl, *lrr;
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int lrh;
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ll = rcu_dereference_protected(l->avl_left,
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lockdep_is_held(&base->lock));
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lr = rcu_dereference_protected(l->avl_right,
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lockdep_is_held(&base->lock));
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lrh = node_height(lr);
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if (lrh <= node_height(ll)) { /* ll: RH+1 */
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RCU_INIT_POINTER(node->avl_left, lr); /* lr: RH or RH+1 */
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RCU_INIT_POINTER(node->avl_right, r); /* r: RH */
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node->avl_height = lrh + 1; /* RH+1 or RH+2 */
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RCU_INIT_POINTER(l->avl_left, ll); /* ll: RH+1 */
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RCU_INIT_POINTER(l->avl_right, node); /* node: RH+1 or RH+2 */
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l->avl_height = node->avl_height + 1;
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RCU_INIT_POINTER(*nodep, l);
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} else { /* ll: RH, lr: RH+1 */
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lrl = rcu_dereference_protected(lr->avl_left,
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lockdep_is_held(&base->lock)); /* lrl: RH or RH-1 */
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lrr = rcu_dereference_protected(lr->avl_right,
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lockdep_is_held(&base->lock)); /* lrr: RH or RH-1 */
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RCU_INIT_POINTER(node->avl_left, lrr); /* lrr: RH or RH-1 */
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RCU_INIT_POINTER(node->avl_right, r); /* r: RH */
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node->avl_height = rh + 1; /* node: RH+1 */
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RCU_INIT_POINTER(l->avl_left, ll); /* ll: RH */
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RCU_INIT_POINTER(l->avl_right, lrl); /* lrl: RH or RH-1 */
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l->avl_height = rh + 1; /* l: RH+1 */
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RCU_INIT_POINTER(lr->avl_left, l); /* l: RH+1 */
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RCU_INIT_POINTER(lr->avl_right, node); /* node: RH+1 */
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lr->avl_height = rh + 2;
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RCU_INIT_POINTER(*nodep, lr);
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}
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} else if (rh > lh + 1) { /* r: LH+2 */
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struct inet_peer *rr, *rl, *rlr, *rll;
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int rlh;
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rr = rcu_dereference_protected(r->avl_right,
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lockdep_is_held(&base->lock));
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rl = rcu_dereference_protected(r->avl_left,
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lockdep_is_held(&base->lock));
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rlh = node_height(rl);
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if (rlh <= node_height(rr)) { /* rr: LH+1 */
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RCU_INIT_POINTER(node->avl_right, rl); /* rl: LH or LH+1 */
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RCU_INIT_POINTER(node->avl_left, l); /* l: LH */
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node->avl_height = rlh + 1; /* LH+1 or LH+2 */
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RCU_INIT_POINTER(r->avl_right, rr); /* rr: LH+1 */
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RCU_INIT_POINTER(r->avl_left, node); /* node: LH+1 or LH+2 */
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r->avl_height = node->avl_height + 1;
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RCU_INIT_POINTER(*nodep, r);
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} else { /* rr: RH, rl: RH+1 */
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rlr = rcu_dereference_protected(rl->avl_right,
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lockdep_is_held(&base->lock)); /* rlr: LH or LH-1 */
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rll = rcu_dereference_protected(rl->avl_left,
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lockdep_is_held(&base->lock)); /* rll: LH or LH-1 */
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RCU_INIT_POINTER(node->avl_right, rll); /* rll: LH or LH-1 */
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RCU_INIT_POINTER(node->avl_left, l); /* l: LH */
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node->avl_height = lh + 1; /* node: LH+1 */
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RCU_INIT_POINTER(r->avl_right, rr); /* rr: LH */
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RCU_INIT_POINTER(r->avl_left, rlr); /* rlr: LH or LH-1 */
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r->avl_height = lh + 1; /* r: LH+1 */
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RCU_INIT_POINTER(rl->avl_right, r); /* r: LH+1 */
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RCU_INIT_POINTER(rl->avl_left, node); /* node: LH+1 */
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rl->avl_height = lh + 2;
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RCU_INIT_POINTER(*nodep, rl);
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}
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} else {
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node->avl_height = (lh > rh ? lh : rh) + 1;
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}
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}
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}
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/* Called with local BH disabled and the pool lock held. */
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#define link_to_pool(n, base) \
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do { \
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n->avl_height = 1; \
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n->avl_left = peer_avl_empty_rcu; \
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n->avl_right = peer_avl_empty_rcu; \
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/* lockless readers can catch us now */ \
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rcu_assign_pointer(**--stackptr, n); \
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peer_avl_rebalance(stack, stackptr, base); \
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} while (0)
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static void inetpeer_free_rcu(struct rcu_head *head)
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{
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kmem_cache_free(peer_cachep, container_of(head, struct inet_peer, rcu));
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}
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/* May be called with local BH enabled. */
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static void unlink_from_pool(struct inet_peer *p, struct inet_peer_base *base)
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{
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int do_free;
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do_free = 0;
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spin_lock_bh(&base->lock);
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/* Check the reference counter. It was artificially incremented by 1
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* in cleanup() function to prevent sudden disappearing. If we can
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* atomically (because of lockless readers) take this last reference,
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* it's safe to remove the node and free it later.
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* We use refcnt=-1 to alert lockless readers this entry is deleted.
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*/
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if (atomic_cmpxchg(&p->refcnt, 1, -1) == 1) {
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struct inet_peer __rcu **stack[PEER_MAXDEPTH];
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struct inet_peer __rcu ***stackptr, ***delp;
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if (lookup(p->v4daddr, stack, base) != p)
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BUG();
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delp = stackptr - 1; /* *delp[0] == p */
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if (p->avl_left == peer_avl_empty_rcu) {
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*delp[0] = p->avl_right;
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--stackptr;
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} else {
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/* look for a node to insert instead of p */
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struct inet_peer *t;
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t = lookup_rightempty(p, base);
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BUG_ON(rcu_dereference_protected(*stackptr[-1],
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lockdep_is_held(&base->lock)) != t);
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**--stackptr = t->avl_left;
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/* t is removed, t->v4daddr > x->v4daddr for any
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* x in p->avl_left subtree.
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* Put t in the old place of p. */
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RCU_INIT_POINTER(*delp[0], t);
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t->avl_left = p->avl_left;
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t->avl_right = p->avl_right;
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t->avl_height = p->avl_height;
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BUG_ON(delp[1] != &p->avl_left);
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delp[1] = &t->avl_left; /* was &p->avl_left */
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}
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peer_avl_rebalance(stack, stackptr, base);
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base->total--;
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do_free = 1;
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}
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spin_unlock_bh(&base->lock);
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if (do_free)
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call_rcu_bh(&p->rcu, inetpeer_free_rcu);
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else
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/* The node is used again. Decrease the reference counter
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* back. The loop "cleanup -> unlink_from_unused
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* -> unlink_from_pool -> putpeer -> link_to_unused
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* -> cleanup (for the same node)"
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* doesn't really exist because the entry will have a
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* recent deletion time and will not be cleaned again soon.
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*/
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inet_putpeer(p);
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}
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static struct inet_peer_base *peer_to_base(struct inet_peer *p)
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{
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return &v4_peers;
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}
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/* May be called with local BH enabled. */
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static int cleanup_once(unsigned long ttl)
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{
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struct inet_peer *p = NULL;
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/* Remove the first entry from the list of unused nodes. */
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spin_lock_bh(&unused_peers.lock);
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if (!list_empty(&unused_peers.list)) {
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__u32 delta;
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p = list_first_entry(&unused_peers.list, struct inet_peer, unused);
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delta = (__u32)jiffies - p->dtime;
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if (delta < ttl) {
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/* Do not prune fresh entries. */
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spin_unlock_bh(&unused_peers.lock);
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return -1;
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}
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list_del_init(&p->unused);
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/* Grab an extra reference to prevent node disappearing
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* before unlink_from_pool() call. */
|
|
atomic_inc(&p->refcnt);
|
|
}
|
|
spin_unlock_bh(&unused_peers.lock);
|
|
|
|
if (p == NULL)
|
|
/* It means that the total number of USED entries has
|
|
* grown over inet_peer_threshold. It shouldn't really
|
|
* happen because of entry limits in route cache. */
|
|
return -1;
|
|
|
|
unlink_from_pool(p, peer_to_base(p));
|
|
return 0;
|
|
}
|
|
|
|
static struct inet_peer_base *family_to_base(int family)
|
|
{
|
|
return &v4_peers;
|
|
}
|
|
|
|
/* Called with or without local BH being disabled. */
|
|
struct inet_peer *inet_getpeer(__be32 daddr, int create)
|
|
{
|
|
struct inet_peer __rcu **stack[PEER_MAXDEPTH], ***stackptr;
|
|
struct inet_peer_base *base = family_to_base(AF_INET);
|
|
struct inet_peer *p;
|
|
|
|
/* Look up for the address quickly, lockless.
|
|
* Because of a concurrent writer, we might not find an existing entry.
|
|
*/
|
|
rcu_read_lock_bh();
|
|
p = lookup_rcu_bh(daddr, base);
|
|
rcu_read_unlock_bh();
|
|
|
|
if (p) {
|
|
/* The existing node has been found.
|
|
* Remove the entry from unused list if it was there.
|
|
*/
|
|
unlink_from_unused(p);
|
|
return p;
|
|
}
|
|
|
|
/* retry an exact lookup, taking the lock before.
|
|
* At least, nodes should be hot in our cache.
|
|
*/
|
|
spin_lock_bh(&base->lock);
|
|
p = lookup(daddr, stack, base);
|
|
if (p != peer_avl_empty) {
|
|
atomic_inc(&p->refcnt);
|
|
spin_unlock_bh(&base->lock);
|
|
/* Remove the entry from unused list if it was there. */
|
|
unlink_from_unused(p);
|
|
return p;
|
|
}
|
|
p = create ? kmem_cache_alloc(peer_cachep, GFP_ATOMIC) : NULL;
|
|
if (p) {
|
|
p->v4daddr = daddr;
|
|
atomic_set(&p->refcnt, 1);
|
|
atomic_set(&p->rid, 0);
|
|
atomic_set(&p->ip_id_count, secure_ip_id(daddr));
|
|
p->tcp_ts_stamp = 0;
|
|
INIT_LIST_HEAD(&p->unused);
|
|
|
|
|
|
/* Link the node. */
|
|
link_to_pool(p, base);
|
|
base->total++;
|
|
}
|
|
spin_unlock_bh(&base->lock);
|
|
|
|
if (base->total >= inet_peer_threshold)
|
|
/* Remove one less-recently-used entry. */
|
|
cleanup_once(0);
|
|
|
|
return p;
|
|
}
|
|
|
|
static int compute_total(void)
|
|
{
|
|
return v4_peers.total;
|
|
}
|
|
|
|
/* Called with local BH disabled. */
|
|
static void peer_check_expire(unsigned long dummy)
|
|
{
|
|
unsigned long now = jiffies;
|
|
int ttl, total;
|
|
|
|
total = compute_total();
|
|
if (total >= inet_peer_threshold)
|
|
ttl = inet_peer_minttl;
|
|
else
|
|
ttl = inet_peer_maxttl
|
|
- (inet_peer_maxttl - inet_peer_minttl) / HZ *
|
|
total / inet_peer_threshold * HZ;
|
|
while (!cleanup_once(ttl)) {
|
|
if (jiffies != now)
|
|
break;
|
|
}
|
|
|
|
/* Trigger the timer after inet_peer_gc_mintime .. inet_peer_gc_maxtime
|
|
* interval depending on the total number of entries (more entries,
|
|
* less interval). */
|
|
total = compute_total();
|
|
if (total >= inet_peer_threshold)
|
|
peer_periodic_timer.expires = jiffies + inet_peer_gc_mintime;
|
|
else
|
|
peer_periodic_timer.expires = jiffies
|
|
+ inet_peer_gc_maxtime
|
|
- (inet_peer_gc_maxtime - inet_peer_gc_mintime) / HZ *
|
|
total / inet_peer_threshold * HZ;
|
|
add_timer(&peer_periodic_timer);
|
|
}
|
|
|
|
void inet_putpeer(struct inet_peer *p)
|
|
{
|
|
local_bh_disable();
|
|
|
|
if (atomic_dec_and_lock(&p->refcnt, &unused_peers.lock)) {
|
|
list_add_tail(&p->unused, &unused_peers.list);
|
|
p->dtime = (__u32)jiffies;
|
|
spin_unlock(&unused_peers.lock);
|
|
}
|
|
|
|
local_bh_enable();
|
|
}
|