![Herbert Xu](/assets/img/avatar_default.png)
Another spin of Herbert Xu's "safer ip reassembly" patch for 2.6.16. (The original patch is here: http://marc.theaimsgroup.com/?l=linux-netdev&m=112281936522415&w=2 and my only contribution is to have tested it.) This patch (optionally) does additional checks before accepting IP fragments, which can greatly reduce the possibility of reassembling fragments which originated from different IP datagrams. Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au> Signed-off-by: Arthur Kepner <akepner@sgi.com> Signed-off-by: David S. Miller <davem@davemloft.net>
463 lines
14 KiB
C
463 lines
14 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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* Version: $Id: inetpeer.c,v 1.7 2001/09/20 21:22:50 davem Exp $
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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/sched.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 write lock held.
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* 2. Nodes may disappear from the tree only with the pool write 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_next, unused_prevp: 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: idlock
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*/
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/* Exported for inet_getid inline function. */
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DEFINE_SPINLOCK(inet_peer_idlock);
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static kmem_cache_t *peer_cachep __read_mostly;
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#define node_height(x) x->avl_height
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static struct inet_peer peer_fake_node = {
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.avl_left = &peer_fake_node,
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.avl_right = &peer_fake_node,
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.avl_height = 0
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};
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#define peer_avl_empty (&peer_fake_node)
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static struct inet_peer *peer_root = peer_avl_empty;
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static DEFINE_RWLOCK(peer_pool_lock);
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#define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */
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static volatile int peer_total;
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/* Exported for sysctl_net_ipv4. */
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int inet_peer_threshold = 65536 + 128; /* start to throw entries more
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* aggressively at this stage */
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int inet_peer_minttl = 120 * HZ; /* TTL under high load: 120 sec */
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int inet_peer_maxttl = 10 * 60 * HZ; /* usual time to live: 10 min */
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static struct inet_peer *inet_peer_unused_head;
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/* Exported for inet_putpeer inline function. */
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struct inet_peer **inet_peer_unused_tailp = &inet_peer_unused_head;
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DEFINE_SPINLOCK(inet_peer_unused_lock);
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#define PEER_MAX_CLEANUP_WORK 30
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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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/* Exported for sysctl_net_ipv4. */
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int inet_peer_gc_mintime = 10 * HZ,
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inet_peer_gc_maxtime = 120 * HZ;
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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,
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NULL, NULL);
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if (!peer_cachep)
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panic("cannot create inet_peer_cache");
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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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spin_lock_bh(&inet_peer_unused_lock);
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if (p->unused_prevp != NULL) {
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/* On unused list. */
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*p->unused_prevp = p->unused_next;
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if (p->unused_next != NULL)
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p->unused_next->unused_prevp = p->unused_prevp;
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else
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inet_peer_unused_tailp = p->unused_prevp;
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p->unused_prevp = NULL; /* mark it as removed */
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}
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spin_unlock_bh(&inet_peer_unused_lock);
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}
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/* Called with local BH disabled and the pool lock held. */
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#define lookup(daddr) \
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({ \
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struct inet_peer *u, **v; \
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stackptr = stack; \
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*stackptr++ = &peer_root; \
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for (u = peer_root; u != peer_avl_empty; ) { \
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if (daddr == u->v4daddr) \
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break; \
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if (daddr < 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 = *v; \
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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 write lock held. */
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#define lookup_rightempty(start) \
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({ \
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struct inet_peer *u, **v; \
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*stackptr++ = &start->avl_left; \
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v = &start->avl_left; \
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for (u = *v; u->avl_right != peer_avl_empty; ) { \
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v = &u->avl_right; \
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*stackptr++ = v; \
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u = *v; \
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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 write 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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static void peer_avl_rebalance(struct inet_peer **stack[],
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struct inet_peer ***stackend)
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{
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struct inet_peer **nodep, *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 = *nodep;
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l = node->avl_left;
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r = node->avl_right;
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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 = l->avl_left;
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lr = l->avl_right;
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lrh = node_height(lr);
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if (lrh <= node_height(ll)) { /* ll: RH+1 */
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node->avl_left = lr; /* lr: RH or RH+1 */
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node->avl_right = r; /* r: RH */
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node->avl_height = lrh + 1; /* RH+1 or RH+2 */
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l->avl_left = ll; /* ll: RH+1 */
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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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*nodep = l;
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} else { /* ll: RH, lr: RH+1 */
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lrl = lr->avl_left; /* lrl: RH or RH-1 */
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lrr = lr->avl_right; /* lrr: RH or RH-1 */
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node->avl_left = lrr; /* lrr: RH or RH-1 */
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node->avl_right = r; /* r: RH */
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node->avl_height = rh + 1; /* node: RH+1 */
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l->avl_left = ll; /* ll: RH */
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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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lr->avl_left = l; /* l: RH+1 */
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lr->avl_right = node; /* node: RH+1 */
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lr->avl_height = rh + 2;
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*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 = r->avl_right;
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rl = r->avl_left;
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rlh = node_height(rl);
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if (rlh <= node_height(rr)) { /* rr: LH+1 */
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node->avl_right = rl; /* rl: LH or LH+1 */
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node->avl_left = l; /* l: LH */
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node->avl_height = rlh + 1; /* LH+1 or LH+2 */
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r->avl_right = rr; /* rr: LH+1 */
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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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*nodep = r;
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} else { /* rr: RH, rl: RH+1 */
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rlr = rl->avl_right; /* rlr: LH or LH-1 */
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rll = rl->avl_left; /* rll: LH or LH-1 */
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node->avl_right = rll; /* rll: LH or LH-1 */
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node->avl_left = l; /* l: LH */
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node->avl_height = lh + 1; /* node: LH+1 */
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r->avl_right = rr; /* rr: LH */
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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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rl->avl_right = r; /* r: LH+1 */
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rl->avl_left = node; /* node: LH+1 */
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rl->avl_height = lh + 2;
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*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 write lock held. */
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#define link_to_pool(n) \
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do { \
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n->avl_height = 1; \
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n->avl_left = peer_avl_empty; \
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n->avl_right = peer_avl_empty; \
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**--stackptr = n; \
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peer_avl_rebalance(stack, stackptr); \
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} while(0)
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/* May be called with local BH enabled. */
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static void unlink_from_pool(struct inet_peer *p)
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{
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int do_free;
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do_free = 0;
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write_lock_bh(&peer_pool_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 the
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* reference count is still 1 then the node is referenced only as `p'
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* here and from the pool. So under the exclusive pool lock it's safe
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* to remove the node and free it later. */
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if (atomic_read(&p->refcnt) == 1) {
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struct inet_peer **stack[PEER_MAXDEPTH];
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struct inet_peer ***stackptr, ***delp;
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if (lookup(p->v4daddr) != 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) {
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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);
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if (*stackptr[-1] != t)
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BUG();
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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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*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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if (delp[1] != &p->avl_left)
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BUG();
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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);
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peer_total--;
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do_free = 1;
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}
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write_unlock_bh(&peer_pool_lock);
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if (do_free)
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kmem_cache_free(peer_cachep, p);
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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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inet_putpeer(p);
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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;
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/* Remove the first entry from the list of unused nodes. */
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spin_lock_bh(&inet_peer_unused_lock);
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p = inet_peer_unused_head;
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if (p != NULL) {
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if (time_after(p->dtime + ttl, jiffies)) {
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/* Do not prune fresh entries. */
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spin_unlock_bh(&inet_peer_unused_lock);
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return -1;
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}
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inet_peer_unused_head = p->unused_next;
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if (p->unused_next != NULL)
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p->unused_next->unused_prevp = p->unused_prevp;
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else
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inet_peer_unused_tailp = p->unused_prevp;
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p->unused_prevp = NULL; /* mark as not on the list */
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/* Grab an extra reference to prevent node disappearing
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* before unlink_from_pool() call. */
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atomic_inc(&p->refcnt);
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}
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spin_unlock_bh(&inet_peer_unused_lock);
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if (p == NULL)
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/* It means that the total number of USED entries has
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* grown over inet_peer_threshold. It shouldn't really
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* happen because of entry limits in route cache. */
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return -1;
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unlink_from_pool(p);
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return 0;
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}
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/* Called with or without local BH being disabled. */
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struct inet_peer *inet_getpeer(__u32 daddr, int create)
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{
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struct inet_peer *p, *n;
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struct inet_peer **stack[PEER_MAXDEPTH], ***stackptr;
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/* Look up for the address quickly. */
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read_lock_bh(&peer_pool_lock);
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p = lookup(daddr);
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if (p != peer_avl_empty)
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atomic_inc(&p->refcnt);
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read_unlock_bh(&peer_pool_lock);
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if (p != peer_avl_empty) {
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/* The existing node has been found. */
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/* Remove the entry from unused list if it was there. */
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unlink_from_unused(p);
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return p;
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}
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if (!create)
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return NULL;
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/* Allocate the space outside the locked region. */
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n = kmem_cache_alloc(peer_cachep, GFP_ATOMIC);
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if (n == NULL)
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return NULL;
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n->v4daddr = daddr;
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atomic_set(&n->refcnt, 1);
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atomic_set(&n->rid, 0);
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n->ip_id_count = secure_ip_id(daddr);
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n->tcp_ts_stamp = 0;
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write_lock_bh(&peer_pool_lock);
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/* Check if an entry has suddenly appeared. */
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p = lookup(daddr);
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if (p != peer_avl_empty)
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goto out_free;
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/* Link the node. */
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link_to_pool(n);
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n->unused_prevp = NULL; /* not on the list */
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peer_total++;
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write_unlock_bh(&peer_pool_lock);
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if (peer_total >= inet_peer_threshold)
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/* Remove one less-recently-used entry. */
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cleanup_once(0);
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return n;
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out_free:
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/* The appropriate node is already in the pool. */
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atomic_inc(&p->refcnt);
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write_unlock_bh(&peer_pool_lock);
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/* Remove the entry from unused list if it was there. */
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unlink_from_unused(p);
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/* Free preallocated the preallocated node. */
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kmem_cache_free(peer_cachep, n);
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return p;
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}
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/* Called with local BH disabled. */
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static void peer_check_expire(unsigned long dummy)
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{
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int i;
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int ttl;
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if (peer_total >= inet_peer_threshold)
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ttl = inet_peer_minttl;
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|
else
|
|
ttl = inet_peer_maxttl
|
|
- (inet_peer_maxttl - inet_peer_minttl) / HZ *
|
|
peer_total / inet_peer_threshold * HZ;
|
|
for (i = 0; i < PEER_MAX_CLEANUP_WORK && !cleanup_once(ttl); i++);
|
|
|
|
/* Trigger the timer after inet_peer_gc_mintime .. inet_peer_gc_maxtime
|
|
* interval depending on the total number of entries (more entries,
|
|
* less interval). */
|
|
if (peer_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 *
|
|
peer_total / inet_peer_threshold * HZ;
|
|
add_timer(&peer_periodic_timer);
|
|
}
|