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1/*
2 * INET An implementation of the TCP/IP protocol suite for the LINUX
3 * operating system. INET is implemented using the BSD Socket
4 * interface as the means of communication with the user level.
5 *
6 * Generic TIME_WAIT sockets functions
7 *
8 * From code orinally in TCP
9 */
10
11#include <linux/kernel.h>
12#include <linux/slab.h>
13#include <linux/module.h>
14#include <net/inet_hashtables.h>
15#include <net/inet_timewait_sock.h>
16#include <net/ip.h>
17
18
19/**
20 * inet_twsk_bind_unhash - unhash a timewait socket from bind hash
21 * @tw: timewait socket
22 * @hashinfo: hashinfo pointer
23 *
24 * unhash a timewait socket from bind hash, if hashed.
25 * bind hash lock must be held by caller.
26 * Returns 1 if caller should call inet_twsk_put() after lock release.
27 */
28void inet_twsk_bind_unhash(struct inet_timewait_sock *tw,
29 struct inet_hashinfo *hashinfo)
30{
31 struct inet_bind_bucket *tb = tw->tw_tb;
32
33 if (!tb)
34 return;
35
36 __hlist_del(&tw->tw_bind_node);
37 tw->tw_tb = NULL;
38 inet_bind_bucket_destroy(hashinfo->bind_bucket_cachep, tb);
39 __sock_put((struct sock *)tw);
40}
41
42/* Must be called with locally disabled BHs. */
43static void inet_twsk_kill(struct inet_timewait_sock *tw)
44{
45 struct inet_hashinfo *hashinfo = tw->tw_dr->hashinfo;
46 spinlock_t *lock = inet_ehash_lockp(hashinfo, tw->tw_hash);
47 struct inet_bind_hashbucket *bhead;
48
49 spin_lock(lock);
50 sk_nulls_del_node_init_rcu((struct sock *)tw);
51 spin_unlock(lock);
52
53 /* Disassociate with bind bucket. */
54 bhead = &hashinfo->bhash[inet_bhashfn(twsk_net(tw), tw->tw_num,
55 hashinfo->bhash_size)];
56
57 spin_lock(&bhead->lock);
58 inet_twsk_bind_unhash(tw, hashinfo);
59 spin_unlock(&bhead->lock);
60
61 atomic_dec(&tw->tw_dr->tw_count);
62 inet_twsk_put(tw);
63}
64
65void inet_twsk_free(struct inet_timewait_sock *tw)
66{
67 struct module *owner = tw->tw_prot->owner;
68 twsk_destructor((struct sock *)tw);
69#ifdef SOCK_REFCNT_DEBUG
70 pr_debug("%s timewait_sock %p released\n", tw->tw_prot->name, tw);
71#endif
72 kmem_cache_free(tw->tw_prot->twsk_prot->twsk_slab, tw);
73 module_put(owner);
74}
75
76void inet_twsk_put(struct inet_timewait_sock *tw)
77{
78 if (refcount_dec_and_test(&tw->tw_refcnt))
79 inet_twsk_free(tw);
80}
81EXPORT_SYMBOL_GPL(inet_twsk_put);
82
83static void inet_twsk_add_node_rcu(struct inet_timewait_sock *tw,
84 struct hlist_nulls_head *list)
85{
86 hlist_nulls_add_head_rcu(&tw->tw_node, list);
87}
88
89static void inet_twsk_add_bind_node(struct inet_timewait_sock *tw,
90 struct hlist_head *list)
91{
92 hlist_add_head(&tw->tw_bind_node, list);
93}
94
95/*
96 * Enter the time wait state. This is called with locally disabled BH.
97 * Essentially we whip up a timewait bucket, copy the relevant info into it
98 * from the SK, and mess with hash chains and list linkage.
99 */
100void inet_twsk_hashdance(struct inet_timewait_sock *tw, struct sock *sk,
101 struct inet_hashinfo *hashinfo)
102{
103 const struct inet_sock *inet = inet_sk(sk);
104 const struct inet_connection_sock *icsk = inet_csk(sk);
105 struct inet_ehash_bucket *ehead = inet_ehash_bucket(hashinfo, sk->sk_hash);
106 spinlock_t *lock = inet_ehash_lockp(hashinfo, sk->sk_hash);
107 struct inet_bind_hashbucket *bhead;
108 /* Step 1: Put TW into bind hash. Original socket stays there too.
109 Note, that any socket with inet->num != 0 MUST be bound in
110 binding cache, even if it is closed.
111 */
112 bhead = &hashinfo->bhash[inet_bhashfn(twsk_net(tw), inet->inet_num,
113 hashinfo->bhash_size)];
114 spin_lock(&bhead->lock);
115 tw->tw_tb = icsk->icsk_bind_hash;
116 WARN_ON(!icsk->icsk_bind_hash);
117 inet_twsk_add_bind_node(tw, &tw->tw_tb->owners);
118 spin_unlock(&bhead->lock);
119
120 spin_lock(lock);
121
122 inet_twsk_add_node_rcu(tw, &ehead->chain);
123
124 /* Step 3: Remove SK from hash chain */
125 if (__sk_nulls_del_node_init_rcu(sk))
126 sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
127
128 spin_unlock(lock);
129
130 /* tw_refcnt is set to 3 because we have :
131 * - one reference for bhash chain.
132 * - one reference for ehash chain.
133 * - one reference for timer.
134 * We can use atomic_set() because prior spin_lock()/spin_unlock()
135 * committed into memory all tw fields.
136 * Also note that after this point, we lost our implicit reference
137 * so we are not allowed to use tw anymore.
138 */
139 refcount_set(&tw->tw_refcnt, 3);
140}
141EXPORT_SYMBOL_GPL(inet_twsk_hashdance);
142
143static void tw_timer_handler(struct timer_list *t)
144{
145 struct inet_timewait_sock *tw = from_timer(tw, t, tw_timer);
146
147 if (tw->tw_kill)
148 __NET_INC_STATS(twsk_net(tw), LINUX_MIB_TIMEWAITKILLED);
149 else
150 __NET_INC_STATS(twsk_net(tw), LINUX_MIB_TIMEWAITED);
151 inet_twsk_kill(tw);
152}
153
154struct inet_timewait_sock *inet_twsk_alloc(const struct sock *sk,
155 struct inet_timewait_death_row *dr,
156 const int state)
157{
158 struct inet_timewait_sock *tw;
159
160 if (atomic_read(&dr->tw_count) >= dr->sysctl_max_tw_buckets)
161 return NULL;
162
163 tw = kmem_cache_alloc(sk->sk_prot_creator->twsk_prot->twsk_slab,
164 GFP_ATOMIC);
165 if (tw) {
166 const struct inet_sock *inet = inet_sk(sk);
167
168 tw->tw_dr = dr;
169 /* Give us an identity. */
170 tw->tw_daddr = inet->inet_daddr;
171 tw->tw_rcv_saddr = inet->inet_rcv_saddr;
172 tw->tw_bound_dev_if = sk->sk_bound_dev_if;
173 tw->tw_tos = inet->tos;
174 tw->tw_num = inet->inet_num;
175 tw->tw_state = TCP_TIME_WAIT;
176 tw->tw_substate = state;
177 tw->tw_sport = inet->inet_sport;
178 tw->tw_dport = inet->inet_dport;
179 tw->tw_family = sk->sk_family;
180 tw->tw_reuse = sk->sk_reuse;
181 tw->tw_reuseport = sk->sk_reuseport;
182 tw->tw_hash = sk->sk_hash;
183 tw->tw_ipv6only = 0;
184 tw->tw_transparent = inet->transparent;
185 tw->tw_prot = sk->sk_prot_creator;
186 atomic64_set(&tw->tw_cookie, atomic64_read(&sk->sk_cookie));
187 twsk_net_set(tw, sock_net(sk));
188 timer_setup(&tw->tw_timer, tw_timer_handler, TIMER_PINNED);
189 /*
190 * Because we use RCU lookups, we should not set tw_refcnt
191 * to a non null value before everything is setup for this
192 * timewait socket.
193 */
194 refcount_set(&tw->tw_refcnt, 0);
195
196 __module_get(tw->tw_prot->owner);
197 }
198
199 return tw;
200}
201EXPORT_SYMBOL_GPL(inet_twsk_alloc);
202
203/* These are always called from BH context. See callers in
204 * tcp_input.c to verify this.
205 */
206
207/* This is for handling early-kills of TIME_WAIT sockets.
208 * Warning : consume reference.
209 * Caller should not access tw anymore.
210 */
211void inet_twsk_deschedule_put(struct inet_timewait_sock *tw)
212{
213 if (del_timer_sync(&tw->tw_timer))
214 inet_twsk_kill(tw);
215 inet_twsk_put(tw);
216}
217EXPORT_SYMBOL(inet_twsk_deschedule_put);
218
219void __inet_twsk_schedule(struct inet_timewait_sock *tw, int timeo, bool rearm)
220{
221 /* timeout := RTO * 3.5
222 *
223 * 3.5 = 1+2+0.5 to wait for two retransmits.
224 *
225 * RATIONALE: if FIN arrived and we entered TIME-WAIT state,
226 * our ACK acking that FIN can be lost. If N subsequent retransmitted
227 * FINs (or previous seqments) are lost (probability of such event
228 * is p^(N+1), where p is probability to lose single packet and
229 * time to detect the loss is about RTO*(2^N - 1) with exponential
230 * backoff). Normal timewait length is calculated so, that we
231 * waited at least for one retransmitted FIN (maximal RTO is 120sec).
232 * [ BTW Linux. following BSD, violates this requirement waiting
233 * only for 60sec, we should wait at least for 240 secs.
234 * Well, 240 consumes too much of resources 8)
235 * ]
236 * This interval is not reduced to catch old duplicate and
237 * responces to our wandering segments living for two MSLs.
238 * However, if we use PAWS to detect
239 * old duplicates, we can reduce the interval to bounds required
240 * by RTO, rather than MSL. So, if peer understands PAWS, we
241 * kill tw bucket after 3.5*RTO (it is important that this number
242 * is greater than TS tick!) and detect old duplicates with help
243 * of PAWS.
244 */
245
246 tw->tw_kill = timeo <= 4*HZ;
247 if (!rearm) {
248 BUG_ON(mod_timer(&tw->tw_timer, jiffies + timeo));
249 atomic_inc(&tw->tw_dr->tw_count);
250 } else {
251 mod_timer_pending(&tw->tw_timer, jiffies + timeo);
252 }
253}
254EXPORT_SYMBOL_GPL(__inet_twsk_schedule);
255
256void inet_twsk_purge(struct inet_hashinfo *hashinfo, int family)
257{
258 struct inet_timewait_sock *tw;
259 struct sock *sk;
260 struct hlist_nulls_node *node;
261 unsigned int slot;
262
263 for (slot = 0; slot <= hashinfo->ehash_mask; slot++) {
264 struct inet_ehash_bucket *head = &hashinfo->ehash[slot];
265restart_rcu:
266 cond_resched();
267 rcu_read_lock();
268restart:
269 sk_nulls_for_each_rcu(sk, node, &head->chain) {
270 if (sk->sk_state != TCP_TIME_WAIT)
271 continue;
272 tw = inet_twsk(sk);
273 if ((tw->tw_family != family) ||
274 refcount_read(&twsk_net(tw)->count))
275 continue;
276
277 if (unlikely(!refcount_inc_not_zero(&tw->tw_refcnt)))
278 continue;
279
280 if (unlikely((tw->tw_family != family) ||
281 refcount_read(&twsk_net(tw)->count))) {
282 inet_twsk_put(tw);
283 goto restart;
284 }
285
286 rcu_read_unlock();
287 local_bh_disable();
288 inet_twsk_deschedule_put(tw);
289 local_bh_enable();
290 goto restart_rcu;
291 }
292 /* If the nulls value we got at the end of this lookup is
293 * not the expected one, we must restart lookup.
294 * We probably met an item that was moved to another chain.
295 */
296 if (get_nulls_value(node) != slot)
297 goto restart;
298 rcu_read_unlock();
299 }
300}
301EXPORT_SYMBOL_GPL(inet_twsk_purge);
1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * INET An implementation of the TCP/IP protocol suite for the LINUX
4 * operating system. INET is implemented using the BSD Socket
5 * interface as the means of communication with the user level.
6 *
7 * Generic TIME_WAIT sockets functions
8 *
9 * From code orinally in TCP
10 */
11
12#include <linux/kernel.h>
13#include <linux/slab.h>
14#include <linux/module.h>
15#include <net/inet_hashtables.h>
16#include <net/inet_timewait_sock.h>
17#include <net/ip.h>
18
19
20/**
21 * inet_twsk_bind_unhash - unhash a timewait socket from bind hash
22 * @tw: timewait socket
23 * @hashinfo: hashinfo pointer
24 *
25 * unhash a timewait socket from bind hash, if hashed.
26 * bind hash lock must be held by caller.
27 * Returns 1 if caller should call inet_twsk_put() after lock release.
28 */
29void inet_twsk_bind_unhash(struct inet_timewait_sock *tw,
30 struct inet_hashinfo *hashinfo)
31{
32 struct inet_bind2_bucket *tb2 = tw->tw_tb2;
33 struct inet_bind_bucket *tb = tw->tw_tb;
34
35 if (!tb)
36 return;
37
38 __sk_del_bind_node((struct sock *)tw);
39 tw->tw_tb = NULL;
40 tw->tw_tb2 = NULL;
41 inet_bind2_bucket_destroy(hashinfo->bind2_bucket_cachep, tb2);
42 inet_bind_bucket_destroy(hashinfo->bind_bucket_cachep, tb);
43
44 __sock_put((struct sock *)tw);
45}
46
47/* Must be called with locally disabled BHs. */
48static void inet_twsk_kill(struct inet_timewait_sock *tw)
49{
50 struct inet_hashinfo *hashinfo = tw->tw_dr->hashinfo;
51 spinlock_t *lock = inet_ehash_lockp(hashinfo, tw->tw_hash);
52 struct inet_bind_hashbucket *bhead, *bhead2;
53
54 spin_lock(lock);
55 sk_nulls_del_node_init_rcu((struct sock *)tw);
56 spin_unlock(lock);
57
58 /* Disassociate with bind bucket. */
59 bhead = &hashinfo->bhash[inet_bhashfn(twsk_net(tw), tw->tw_num,
60 hashinfo->bhash_size)];
61 bhead2 = inet_bhashfn_portaddr(hashinfo, (struct sock *)tw,
62 twsk_net(tw), tw->tw_num);
63
64 spin_lock(&bhead->lock);
65 spin_lock(&bhead2->lock);
66 inet_twsk_bind_unhash(tw, hashinfo);
67 spin_unlock(&bhead2->lock);
68 spin_unlock(&bhead->lock);
69
70 refcount_dec(&tw->tw_dr->tw_refcount);
71 inet_twsk_put(tw);
72}
73
74void inet_twsk_free(struct inet_timewait_sock *tw)
75{
76 struct module *owner = tw->tw_prot->owner;
77 twsk_destructor((struct sock *)tw);
78 kmem_cache_free(tw->tw_prot->twsk_prot->twsk_slab, tw);
79 module_put(owner);
80}
81
82void inet_twsk_put(struct inet_timewait_sock *tw)
83{
84 if (refcount_dec_and_test(&tw->tw_refcnt))
85 inet_twsk_free(tw);
86}
87EXPORT_SYMBOL_GPL(inet_twsk_put);
88
89static void inet_twsk_add_node_rcu(struct inet_timewait_sock *tw,
90 struct hlist_nulls_head *list)
91{
92 hlist_nulls_add_head_rcu(&tw->tw_node, list);
93}
94
95/*
96 * Enter the time wait state. This is called with locally disabled BH.
97 * Essentially we whip up a timewait bucket, copy the relevant info into it
98 * from the SK, and mess with hash chains and list linkage.
99 */
100void inet_twsk_hashdance(struct inet_timewait_sock *tw, struct sock *sk,
101 struct inet_hashinfo *hashinfo)
102{
103 const struct inet_sock *inet = inet_sk(sk);
104 const struct inet_connection_sock *icsk = inet_csk(sk);
105 struct inet_ehash_bucket *ehead = inet_ehash_bucket(hashinfo, sk->sk_hash);
106 spinlock_t *lock = inet_ehash_lockp(hashinfo, sk->sk_hash);
107 struct inet_bind_hashbucket *bhead, *bhead2;
108
109 /* Step 1: Put TW into bind hash. Original socket stays there too.
110 Note, that any socket with inet->num != 0 MUST be bound in
111 binding cache, even if it is closed.
112 */
113 bhead = &hashinfo->bhash[inet_bhashfn(twsk_net(tw), inet->inet_num,
114 hashinfo->bhash_size)];
115 bhead2 = inet_bhashfn_portaddr(hashinfo, sk, twsk_net(tw), inet->inet_num);
116
117 spin_lock(&bhead->lock);
118 spin_lock(&bhead2->lock);
119
120 tw->tw_tb = icsk->icsk_bind_hash;
121 WARN_ON(!icsk->icsk_bind_hash);
122
123 tw->tw_tb2 = icsk->icsk_bind2_hash;
124 WARN_ON(!icsk->icsk_bind2_hash);
125 sk_add_bind_node((struct sock *)tw, &tw->tw_tb2->owners);
126
127 spin_unlock(&bhead2->lock);
128 spin_unlock(&bhead->lock);
129
130 spin_lock(lock);
131
132 inet_twsk_add_node_rcu(tw, &ehead->chain);
133
134 /* Step 3: Remove SK from hash chain */
135 if (__sk_nulls_del_node_init_rcu(sk))
136 sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
137
138 spin_unlock(lock);
139
140 /* tw_refcnt is set to 3 because we have :
141 * - one reference for bhash chain.
142 * - one reference for ehash chain.
143 * - one reference for timer.
144 * We can use atomic_set() because prior spin_lock()/spin_unlock()
145 * committed into memory all tw fields.
146 * Also note that after this point, we lost our implicit reference
147 * so we are not allowed to use tw anymore.
148 */
149 refcount_set(&tw->tw_refcnt, 3);
150}
151EXPORT_SYMBOL_GPL(inet_twsk_hashdance);
152
153static void tw_timer_handler(struct timer_list *t)
154{
155 struct inet_timewait_sock *tw = from_timer(tw, t, tw_timer);
156
157 inet_twsk_kill(tw);
158}
159
160struct inet_timewait_sock *inet_twsk_alloc(const struct sock *sk,
161 struct inet_timewait_death_row *dr,
162 const int state)
163{
164 struct inet_timewait_sock *tw;
165
166 if (refcount_read(&dr->tw_refcount) - 1 >=
167 READ_ONCE(dr->sysctl_max_tw_buckets))
168 return NULL;
169
170 tw = kmem_cache_alloc(sk->sk_prot_creator->twsk_prot->twsk_slab,
171 GFP_ATOMIC);
172 if (tw) {
173 const struct inet_sock *inet = inet_sk(sk);
174
175 tw->tw_dr = dr;
176 /* Give us an identity. */
177 tw->tw_daddr = inet->inet_daddr;
178 tw->tw_rcv_saddr = inet->inet_rcv_saddr;
179 tw->tw_bound_dev_if = sk->sk_bound_dev_if;
180 tw->tw_tos = inet->tos;
181 tw->tw_num = inet->inet_num;
182 tw->tw_state = TCP_TIME_WAIT;
183 tw->tw_substate = state;
184 tw->tw_sport = inet->inet_sport;
185 tw->tw_dport = inet->inet_dport;
186 tw->tw_family = sk->sk_family;
187 tw->tw_reuse = sk->sk_reuse;
188 tw->tw_reuseport = sk->sk_reuseport;
189 tw->tw_hash = sk->sk_hash;
190 tw->tw_ipv6only = 0;
191 tw->tw_transparent = inet_test_bit(TRANSPARENT, sk);
192 tw->tw_prot = sk->sk_prot_creator;
193 atomic64_set(&tw->tw_cookie, atomic64_read(&sk->sk_cookie));
194 twsk_net_set(tw, sock_net(sk));
195 timer_setup(&tw->tw_timer, tw_timer_handler, TIMER_PINNED);
196 /*
197 * Because we use RCU lookups, we should not set tw_refcnt
198 * to a non null value before everything is setup for this
199 * timewait socket.
200 */
201 refcount_set(&tw->tw_refcnt, 0);
202
203 __module_get(tw->tw_prot->owner);
204 }
205
206 return tw;
207}
208EXPORT_SYMBOL_GPL(inet_twsk_alloc);
209
210/* These are always called from BH context. See callers in
211 * tcp_input.c to verify this.
212 */
213
214/* This is for handling early-kills of TIME_WAIT sockets.
215 * Warning : consume reference.
216 * Caller should not access tw anymore.
217 */
218void inet_twsk_deschedule_put(struct inet_timewait_sock *tw)
219{
220 if (del_timer_sync(&tw->tw_timer))
221 inet_twsk_kill(tw);
222 inet_twsk_put(tw);
223}
224EXPORT_SYMBOL(inet_twsk_deschedule_put);
225
226void __inet_twsk_schedule(struct inet_timewait_sock *tw, int timeo, bool rearm)
227{
228 /* timeout := RTO * 3.5
229 *
230 * 3.5 = 1+2+0.5 to wait for two retransmits.
231 *
232 * RATIONALE: if FIN arrived and we entered TIME-WAIT state,
233 * our ACK acking that FIN can be lost. If N subsequent retransmitted
234 * FINs (or previous seqments) are lost (probability of such event
235 * is p^(N+1), where p is probability to lose single packet and
236 * time to detect the loss is about RTO*(2^N - 1) with exponential
237 * backoff). Normal timewait length is calculated so, that we
238 * waited at least for one retransmitted FIN (maximal RTO is 120sec).
239 * [ BTW Linux. following BSD, violates this requirement waiting
240 * only for 60sec, we should wait at least for 240 secs.
241 * Well, 240 consumes too much of resources 8)
242 * ]
243 * This interval is not reduced to catch old duplicate and
244 * responces to our wandering segments living for two MSLs.
245 * However, if we use PAWS to detect
246 * old duplicates, we can reduce the interval to bounds required
247 * by RTO, rather than MSL. So, if peer understands PAWS, we
248 * kill tw bucket after 3.5*RTO (it is important that this number
249 * is greater than TS tick!) and detect old duplicates with help
250 * of PAWS.
251 */
252
253 if (!rearm) {
254 bool kill = timeo <= 4*HZ;
255
256 __NET_INC_STATS(twsk_net(tw), kill ? LINUX_MIB_TIMEWAITKILLED :
257 LINUX_MIB_TIMEWAITED);
258 BUG_ON(mod_timer(&tw->tw_timer, jiffies + timeo));
259 refcount_inc(&tw->tw_dr->tw_refcount);
260 } else {
261 mod_timer_pending(&tw->tw_timer, jiffies + timeo);
262 }
263}
264EXPORT_SYMBOL_GPL(__inet_twsk_schedule);
265
266void inet_twsk_purge(struct inet_hashinfo *hashinfo, int family)
267{
268 struct inet_timewait_sock *tw;
269 struct sock *sk;
270 struct hlist_nulls_node *node;
271 unsigned int slot;
272
273 for (slot = 0; slot <= hashinfo->ehash_mask; slot++) {
274 struct inet_ehash_bucket *head = &hashinfo->ehash[slot];
275restart_rcu:
276 cond_resched();
277 rcu_read_lock();
278restart:
279 sk_nulls_for_each_rcu(sk, node, &head->chain) {
280 if (sk->sk_state != TCP_TIME_WAIT) {
281 /* A kernel listener socket might not hold refcnt for net,
282 * so reqsk_timer_handler() could be fired after net is
283 * freed. Userspace listener and reqsk never exist here.
284 */
285 if (unlikely(sk->sk_state == TCP_NEW_SYN_RECV &&
286 hashinfo->pernet)) {
287 struct request_sock *req = inet_reqsk(sk);
288
289 inet_csk_reqsk_queue_drop_and_put(req->rsk_listener, req);
290 }
291
292 continue;
293 }
294
295 tw = inet_twsk(sk);
296 if ((tw->tw_family != family) ||
297 refcount_read(&twsk_net(tw)->ns.count))
298 continue;
299
300 if (unlikely(!refcount_inc_not_zero(&tw->tw_refcnt)))
301 continue;
302
303 if (unlikely((tw->tw_family != family) ||
304 refcount_read(&twsk_net(tw)->ns.count))) {
305 inet_twsk_put(tw);
306 goto restart;
307 }
308
309 rcu_read_unlock();
310 local_bh_disable();
311 inet_twsk_deschedule_put(tw);
312 local_bh_enable();
313 goto restart_rcu;
314 }
315 /* If the nulls value we got at the end of this lookup is
316 * not the expected one, we must restart lookup.
317 * We probably met an item that was moved to another chain.
318 */
319 if (get_nulls_value(node) != slot)
320 goto restart;
321 rcu_read_unlock();
322 }
323}
324EXPORT_SYMBOL_GPL(inet_twsk_purge);