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1/*
2 * inet fragments management
3 *
4 * This program is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU General Public License
6 * as published by the Free Software Foundation; either version
7 * 2 of the License, or (at your option) any later version.
8 *
9 * Authors: Pavel Emelyanov <xemul@openvz.org>
10 * Started as consolidation of ipv4/ip_fragment.c,
11 * ipv6/reassembly. and ipv6 nf conntrack reassembly
12 */
13
14#include <linux/list.h>
15#include <linux/spinlock.h>
16#include <linux/module.h>
17#include <linux/timer.h>
18#include <linux/mm.h>
19#include <linux/random.h>
20#include <linux/skbuff.h>
21#include <linux/rtnetlink.h>
22#include <linux/slab.h>
23
24#include <net/inet_frag.h>
25
26static void inet_frag_secret_rebuild(unsigned long dummy)
27{
28 struct inet_frags *f = (struct inet_frags *)dummy;
29 unsigned long now = jiffies;
30 int i;
31
32 write_lock(&f->lock);
33 get_random_bytes(&f->rnd, sizeof(u32));
34 for (i = 0; i < INETFRAGS_HASHSZ; i++) {
35 struct inet_frag_queue *q;
36 struct hlist_node *p, *n;
37
38 hlist_for_each_entry_safe(q, p, n, &f->hash[i], list) {
39 unsigned int hval = f->hashfn(q);
40
41 if (hval != i) {
42 hlist_del(&q->list);
43
44 /* Relink to new hash chain. */
45 hlist_add_head(&q->list, &f->hash[hval]);
46 }
47 }
48 }
49 write_unlock(&f->lock);
50
51 mod_timer(&f->secret_timer, now + f->secret_interval);
52}
53
54void inet_frags_init(struct inet_frags *f)
55{
56 int i;
57
58 for (i = 0; i < INETFRAGS_HASHSZ; i++)
59 INIT_HLIST_HEAD(&f->hash[i]);
60
61 rwlock_init(&f->lock);
62
63 f->rnd = (u32) ((num_physpages ^ (num_physpages>>7)) ^
64 (jiffies ^ (jiffies >> 6)));
65
66 setup_timer(&f->secret_timer, inet_frag_secret_rebuild,
67 (unsigned long)f);
68 f->secret_timer.expires = jiffies + f->secret_interval;
69 add_timer(&f->secret_timer);
70}
71EXPORT_SYMBOL(inet_frags_init);
72
73void inet_frags_init_net(struct netns_frags *nf)
74{
75 nf->nqueues = 0;
76 atomic_set(&nf->mem, 0);
77 INIT_LIST_HEAD(&nf->lru_list);
78}
79EXPORT_SYMBOL(inet_frags_init_net);
80
81void inet_frags_fini(struct inet_frags *f)
82{
83 del_timer(&f->secret_timer);
84}
85EXPORT_SYMBOL(inet_frags_fini);
86
87void inet_frags_exit_net(struct netns_frags *nf, struct inet_frags *f)
88{
89 nf->low_thresh = 0;
90
91 local_bh_disable();
92 inet_frag_evictor(nf, f);
93 local_bh_enable();
94}
95EXPORT_SYMBOL(inet_frags_exit_net);
96
97static inline void fq_unlink(struct inet_frag_queue *fq, struct inet_frags *f)
98{
99 write_lock(&f->lock);
100 hlist_del(&fq->list);
101 list_del(&fq->lru_list);
102 fq->net->nqueues--;
103 write_unlock(&f->lock);
104}
105
106void inet_frag_kill(struct inet_frag_queue *fq, struct inet_frags *f)
107{
108 if (del_timer(&fq->timer))
109 atomic_dec(&fq->refcnt);
110
111 if (!(fq->last_in & INET_FRAG_COMPLETE)) {
112 fq_unlink(fq, f);
113 atomic_dec(&fq->refcnt);
114 fq->last_in |= INET_FRAG_COMPLETE;
115 }
116}
117EXPORT_SYMBOL(inet_frag_kill);
118
119static inline void frag_kfree_skb(struct netns_frags *nf, struct inet_frags *f,
120 struct sk_buff *skb, int *work)
121{
122 if (work)
123 *work -= skb->truesize;
124
125 atomic_sub(skb->truesize, &nf->mem);
126 if (f->skb_free)
127 f->skb_free(skb);
128 kfree_skb(skb);
129}
130
131void inet_frag_destroy(struct inet_frag_queue *q, struct inet_frags *f,
132 int *work)
133{
134 struct sk_buff *fp;
135 struct netns_frags *nf;
136
137 WARN_ON(!(q->last_in & INET_FRAG_COMPLETE));
138 WARN_ON(del_timer(&q->timer) != 0);
139
140 /* Release all fragment data. */
141 fp = q->fragments;
142 nf = q->net;
143 while (fp) {
144 struct sk_buff *xp = fp->next;
145
146 frag_kfree_skb(nf, f, fp, work);
147 fp = xp;
148 }
149
150 if (work)
151 *work -= f->qsize;
152 atomic_sub(f->qsize, &nf->mem);
153
154 if (f->destructor)
155 f->destructor(q);
156 kfree(q);
157
158}
159EXPORT_SYMBOL(inet_frag_destroy);
160
161int inet_frag_evictor(struct netns_frags *nf, struct inet_frags *f)
162{
163 struct inet_frag_queue *q;
164 int work, evicted = 0;
165
166 work = atomic_read(&nf->mem) - nf->low_thresh;
167 while (work > 0) {
168 read_lock(&f->lock);
169 if (list_empty(&nf->lru_list)) {
170 read_unlock(&f->lock);
171 break;
172 }
173
174 q = list_first_entry(&nf->lru_list,
175 struct inet_frag_queue, lru_list);
176 atomic_inc(&q->refcnt);
177 read_unlock(&f->lock);
178
179 spin_lock(&q->lock);
180 if (!(q->last_in & INET_FRAG_COMPLETE))
181 inet_frag_kill(q, f);
182 spin_unlock(&q->lock);
183
184 if (atomic_dec_and_test(&q->refcnt))
185 inet_frag_destroy(q, f, &work);
186 evicted++;
187 }
188
189 return evicted;
190}
191EXPORT_SYMBOL(inet_frag_evictor);
192
193static struct inet_frag_queue *inet_frag_intern(struct netns_frags *nf,
194 struct inet_frag_queue *qp_in, struct inet_frags *f,
195 void *arg)
196{
197 struct inet_frag_queue *qp;
198#ifdef CONFIG_SMP
199 struct hlist_node *n;
200#endif
201 unsigned int hash;
202
203 write_lock(&f->lock);
204 /*
205 * While we stayed w/o the lock other CPU could update
206 * the rnd seed, so we need to re-calculate the hash
207 * chain. Fortunatelly the qp_in can be used to get one.
208 */
209 hash = f->hashfn(qp_in);
210#ifdef CONFIG_SMP
211 /* With SMP race we have to recheck hash table, because
212 * such entry could be created on other cpu, while we
213 * promoted read lock to write lock.
214 */
215 hlist_for_each_entry(qp, n, &f->hash[hash], list) {
216 if (qp->net == nf && f->match(qp, arg)) {
217 atomic_inc(&qp->refcnt);
218 write_unlock(&f->lock);
219 qp_in->last_in |= INET_FRAG_COMPLETE;
220 inet_frag_put(qp_in, f);
221 return qp;
222 }
223 }
224#endif
225 qp = qp_in;
226 if (!mod_timer(&qp->timer, jiffies + nf->timeout))
227 atomic_inc(&qp->refcnt);
228
229 atomic_inc(&qp->refcnt);
230 hlist_add_head(&qp->list, &f->hash[hash]);
231 list_add_tail(&qp->lru_list, &nf->lru_list);
232 nf->nqueues++;
233 write_unlock(&f->lock);
234 return qp;
235}
236
237static struct inet_frag_queue *inet_frag_alloc(struct netns_frags *nf,
238 struct inet_frags *f, void *arg)
239{
240 struct inet_frag_queue *q;
241
242 q = kzalloc(f->qsize, GFP_ATOMIC);
243 if (q == NULL)
244 return NULL;
245
246 f->constructor(q, arg);
247 atomic_add(f->qsize, &nf->mem);
248 setup_timer(&q->timer, f->frag_expire, (unsigned long)q);
249 spin_lock_init(&q->lock);
250 atomic_set(&q->refcnt, 1);
251 q->net = nf;
252
253 return q;
254}
255
256static struct inet_frag_queue *inet_frag_create(struct netns_frags *nf,
257 struct inet_frags *f, void *arg)
258{
259 struct inet_frag_queue *q;
260
261 q = inet_frag_alloc(nf, f, arg);
262 if (q == NULL)
263 return NULL;
264
265 return inet_frag_intern(nf, q, f, arg);
266}
267
268struct inet_frag_queue *inet_frag_find(struct netns_frags *nf,
269 struct inet_frags *f, void *key, unsigned int hash)
270 __releases(&f->lock)
271{
272 struct inet_frag_queue *q;
273 struct hlist_node *n;
274
275 hlist_for_each_entry(q, n, &f->hash[hash], list) {
276 if (q->net == nf && f->match(q, key)) {
277 atomic_inc(&q->refcnt);
278 read_unlock(&f->lock);
279 return q;
280 }
281 }
282 read_unlock(&f->lock);
283
284 return inet_frag_create(nf, f, key);
285}
286EXPORT_SYMBOL(inet_frag_find);
1/*
2 * inet fragments management
3 *
4 * This program is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU General Public License
6 * as published by the Free Software Foundation; either version
7 * 2 of the License, or (at your option) any later version.
8 *
9 * Authors: Pavel Emelyanov <xemul@openvz.org>
10 * Started as consolidation of ipv4/ip_fragment.c,
11 * ipv6/reassembly. and ipv6 nf conntrack reassembly
12 */
13
14#include <linux/list.h>
15#include <linux/spinlock.h>
16#include <linux/module.h>
17#include <linux/timer.h>
18#include <linux/mm.h>
19#include <linux/random.h>
20#include <linux/skbuff.h>
21#include <linux/rtnetlink.h>
22#include <linux/slab.h>
23
24#include <net/sock.h>
25#include <net/inet_frag.h>
26#include <net/inet_ecn.h>
27
28#define INETFRAGS_EVICT_BUCKETS 128
29#define INETFRAGS_EVICT_MAX 512
30
31/* don't rebuild inetfrag table with new secret more often than this */
32#define INETFRAGS_MIN_REBUILD_INTERVAL (5 * HZ)
33
34/* Given the OR values of all fragments, apply RFC 3168 5.3 requirements
35 * Value : 0xff if frame should be dropped.
36 * 0 or INET_ECN_CE value, to be ORed in to final iph->tos field
37 */
38const u8 ip_frag_ecn_table[16] = {
39 /* at least one fragment had CE, and others ECT_0 or ECT_1 */
40 [IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0] = INET_ECN_CE,
41 [IPFRAG_ECN_CE | IPFRAG_ECN_ECT_1] = INET_ECN_CE,
42 [IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0 | IPFRAG_ECN_ECT_1] = INET_ECN_CE,
43
44 /* invalid combinations : drop frame */
45 [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE] = 0xff,
46 [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_ECT_0] = 0xff,
47 [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_ECT_1] = 0xff,
48 [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_ECT_0 | IPFRAG_ECN_ECT_1] = 0xff,
49 [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0] = 0xff,
50 [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE | IPFRAG_ECN_ECT_1] = 0xff,
51 [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0 | IPFRAG_ECN_ECT_1] = 0xff,
52};
53EXPORT_SYMBOL(ip_frag_ecn_table);
54
55static unsigned int
56inet_frag_hashfn(const struct inet_frags *f, const struct inet_frag_queue *q)
57{
58 return f->hashfn(q) & (INETFRAGS_HASHSZ - 1);
59}
60
61static bool inet_frag_may_rebuild(struct inet_frags *f)
62{
63 return time_after(jiffies,
64 f->last_rebuild_jiffies + INETFRAGS_MIN_REBUILD_INTERVAL);
65}
66
67static void inet_frag_secret_rebuild(struct inet_frags *f)
68{
69 int i;
70
71 write_seqlock_bh(&f->rnd_seqlock);
72
73 if (!inet_frag_may_rebuild(f))
74 goto out;
75
76 get_random_bytes(&f->rnd, sizeof(u32));
77
78 for (i = 0; i < INETFRAGS_HASHSZ; i++) {
79 struct inet_frag_bucket *hb;
80 struct inet_frag_queue *q;
81 struct hlist_node *n;
82
83 hb = &f->hash[i];
84 spin_lock(&hb->chain_lock);
85
86 hlist_for_each_entry_safe(q, n, &hb->chain, list) {
87 unsigned int hval = inet_frag_hashfn(f, q);
88
89 if (hval != i) {
90 struct inet_frag_bucket *hb_dest;
91
92 hlist_del(&q->list);
93
94 /* Relink to new hash chain. */
95 hb_dest = &f->hash[hval];
96
97 /* This is the only place where we take
98 * another chain_lock while already holding
99 * one. As this will not run concurrently,
100 * we cannot deadlock on hb_dest lock below, if its
101 * already locked it will be released soon since
102 * other caller cannot be waiting for hb lock
103 * that we've taken above.
104 */
105 spin_lock_nested(&hb_dest->chain_lock,
106 SINGLE_DEPTH_NESTING);
107 hlist_add_head(&q->list, &hb_dest->chain);
108 spin_unlock(&hb_dest->chain_lock);
109 }
110 }
111 spin_unlock(&hb->chain_lock);
112 }
113
114 f->rebuild = false;
115 f->last_rebuild_jiffies = jiffies;
116out:
117 write_sequnlock_bh(&f->rnd_seqlock);
118}
119
120static bool inet_fragq_should_evict(const struct inet_frag_queue *q)
121{
122 return q->net->low_thresh == 0 ||
123 frag_mem_limit(q->net) >= q->net->low_thresh;
124}
125
126static unsigned int
127inet_evict_bucket(struct inet_frags *f, struct inet_frag_bucket *hb)
128{
129 struct inet_frag_queue *fq;
130 struct hlist_node *n;
131 unsigned int evicted = 0;
132 HLIST_HEAD(expired);
133
134 spin_lock(&hb->chain_lock);
135
136 hlist_for_each_entry_safe(fq, n, &hb->chain, list) {
137 if (!inet_fragq_should_evict(fq))
138 continue;
139
140 if (!del_timer(&fq->timer))
141 continue;
142
143 hlist_add_head(&fq->list_evictor, &expired);
144 ++evicted;
145 }
146
147 spin_unlock(&hb->chain_lock);
148
149 hlist_for_each_entry_safe(fq, n, &expired, list_evictor)
150 f->frag_expire((unsigned long) fq);
151
152 return evicted;
153}
154
155static void inet_frag_worker(struct work_struct *work)
156{
157 unsigned int budget = INETFRAGS_EVICT_BUCKETS;
158 unsigned int i, evicted = 0;
159 struct inet_frags *f;
160
161 f = container_of(work, struct inet_frags, frags_work);
162
163 BUILD_BUG_ON(INETFRAGS_EVICT_BUCKETS >= INETFRAGS_HASHSZ);
164
165 local_bh_disable();
166
167 for (i = ACCESS_ONCE(f->next_bucket); budget; --budget) {
168 evicted += inet_evict_bucket(f, &f->hash[i]);
169 i = (i + 1) & (INETFRAGS_HASHSZ - 1);
170 if (evicted > INETFRAGS_EVICT_MAX)
171 break;
172 }
173
174 f->next_bucket = i;
175
176 local_bh_enable();
177
178 if (f->rebuild && inet_frag_may_rebuild(f))
179 inet_frag_secret_rebuild(f);
180}
181
182static void inet_frag_schedule_worker(struct inet_frags *f)
183{
184 if (unlikely(!work_pending(&f->frags_work)))
185 schedule_work(&f->frags_work);
186}
187
188int inet_frags_init(struct inet_frags *f)
189{
190 int i;
191
192 INIT_WORK(&f->frags_work, inet_frag_worker);
193
194 for (i = 0; i < INETFRAGS_HASHSZ; i++) {
195 struct inet_frag_bucket *hb = &f->hash[i];
196
197 spin_lock_init(&hb->chain_lock);
198 INIT_HLIST_HEAD(&hb->chain);
199 }
200
201 seqlock_init(&f->rnd_seqlock);
202 f->last_rebuild_jiffies = 0;
203 f->frags_cachep = kmem_cache_create(f->frags_cache_name, f->qsize, 0, 0,
204 NULL);
205 if (!f->frags_cachep)
206 return -ENOMEM;
207
208 return 0;
209}
210EXPORT_SYMBOL(inet_frags_init);
211
212void inet_frags_fini(struct inet_frags *f)
213{
214 cancel_work_sync(&f->frags_work);
215 kmem_cache_destroy(f->frags_cachep);
216}
217EXPORT_SYMBOL(inet_frags_fini);
218
219void inet_frags_exit_net(struct netns_frags *nf, struct inet_frags *f)
220{
221 unsigned int seq;
222 int i;
223
224 nf->low_thresh = 0;
225
226evict_again:
227 local_bh_disable();
228 seq = read_seqbegin(&f->rnd_seqlock);
229
230 for (i = 0; i < INETFRAGS_HASHSZ ; i++)
231 inet_evict_bucket(f, &f->hash[i]);
232
233 local_bh_enable();
234 cond_resched();
235
236 if (read_seqretry(&f->rnd_seqlock, seq) ||
237 percpu_counter_sum(&nf->mem))
238 goto evict_again;
239
240 percpu_counter_destroy(&nf->mem);
241}
242EXPORT_SYMBOL(inet_frags_exit_net);
243
244static struct inet_frag_bucket *
245get_frag_bucket_locked(struct inet_frag_queue *fq, struct inet_frags *f)
246__acquires(hb->chain_lock)
247{
248 struct inet_frag_bucket *hb;
249 unsigned int seq, hash;
250
251 restart:
252 seq = read_seqbegin(&f->rnd_seqlock);
253
254 hash = inet_frag_hashfn(f, fq);
255 hb = &f->hash[hash];
256
257 spin_lock(&hb->chain_lock);
258 if (read_seqretry(&f->rnd_seqlock, seq)) {
259 spin_unlock(&hb->chain_lock);
260 goto restart;
261 }
262
263 return hb;
264}
265
266static inline void fq_unlink(struct inet_frag_queue *fq, struct inet_frags *f)
267{
268 struct inet_frag_bucket *hb;
269
270 hb = get_frag_bucket_locked(fq, f);
271 hlist_del(&fq->list);
272 fq->flags |= INET_FRAG_COMPLETE;
273 spin_unlock(&hb->chain_lock);
274}
275
276void inet_frag_kill(struct inet_frag_queue *fq, struct inet_frags *f)
277{
278 if (del_timer(&fq->timer))
279 atomic_dec(&fq->refcnt);
280
281 if (!(fq->flags & INET_FRAG_COMPLETE)) {
282 fq_unlink(fq, f);
283 atomic_dec(&fq->refcnt);
284 }
285}
286EXPORT_SYMBOL(inet_frag_kill);
287
288void inet_frag_destroy(struct inet_frag_queue *q, struct inet_frags *f)
289{
290 struct sk_buff *fp;
291 struct netns_frags *nf;
292 unsigned int sum, sum_truesize = 0;
293
294 WARN_ON(!(q->flags & INET_FRAG_COMPLETE));
295 WARN_ON(del_timer(&q->timer) != 0);
296
297 /* Release all fragment data. */
298 fp = q->fragments;
299 nf = q->net;
300 while (fp) {
301 struct sk_buff *xp = fp->next;
302
303 sum_truesize += fp->truesize;
304 kfree_skb(fp);
305 fp = xp;
306 }
307 sum = sum_truesize + f->qsize;
308
309 if (f->destructor)
310 f->destructor(q);
311 kmem_cache_free(f->frags_cachep, q);
312
313 sub_frag_mem_limit(nf, sum);
314}
315EXPORT_SYMBOL(inet_frag_destroy);
316
317static struct inet_frag_queue *inet_frag_intern(struct netns_frags *nf,
318 struct inet_frag_queue *qp_in,
319 struct inet_frags *f,
320 void *arg)
321{
322 struct inet_frag_bucket *hb = get_frag_bucket_locked(qp_in, f);
323 struct inet_frag_queue *qp;
324
325#ifdef CONFIG_SMP
326 /* With SMP race we have to recheck hash table, because
327 * such entry could have been created on other cpu before
328 * we acquired hash bucket lock.
329 */
330 hlist_for_each_entry(qp, &hb->chain, list) {
331 if (qp->net == nf && f->match(qp, arg)) {
332 atomic_inc(&qp->refcnt);
333 spin_unlock(&hb->chain_lock);
334 qp_in->flags |= INET_FRAG_COMPLETE;
335 inet_frag_put(qp_in, f);
336 return qp;
337 }
338 }
339#endif
340 qp = qp_in;
341 if (!mod_timer(&qp->timer, jiffies + nf->timeout))
342 atomic_inc(&qp->refcnt);
343
344 atomic_inc(&qp->refcnt);
345 hlist_add_head(&qp->list, &hb->chain);
346
347 spin_unlock(&hb->chain_lock);
348
349 return qp;
350}
351
352static struct inet_frag_queue *inet_frag_alloc(struct netns_frags *nf,
353 struct inet_frags *f,
354 void *arg)
355{
356 struct inet_frag_queue *q;
357
358 if (frag_mem_limit(nf) > nf->high_thresh) {
359 inet_frag_schedule_worker(f);
360 return NULL;
361 }
362
363 q = kmem_cache_zalloc(f->frags_cachep, GFP_ATOMIC);
364 if (!q)
365 return NULL;
366
367 q->net = nf;
368 f->constructor(q, arg);
369 add_frag_mem_limit(nf, f->qsize);
370
371 setup_timer(&q->timer, f->frag_expire, (unsigned long)q);
372 spin_lock_init(&q->lock);
373 atomic_set(&q->refcnt, 1);
374
375 return q;
376}
377
378static struct inet_frag_queue *inet_frag_create(struct netns_frags *nf,
379 struct inet_frags *f,
380 void *arg)
381{
382 struct inet_frag_queue *q;
383
384 q = inet_frag_alloc(nf, f, arg);
385 if (!q)
386 return NULL;
387
388 return inet_frag_intern(nf, q, f, arg);
389}
390
391struct inet_frag_queue *inet_frag_find(struct netns_frags *nf,
392 struct inet_frags *f, void *key,
393 unsigned int hash)
394{
395 struct inet_frag_bucket *hb;
396 struct inet_frag_queue *q;
397 int depth = 0;
398
399 if (frag_mem_limit(nf) > nf->low_thresh)
400 inet_frag_schedule_worker(f);
401
402 hash &= (INETFRAGS_HASHSZ - 1);
403 hb = &f->hash[hash];
404
405 spin_lock(&hb->chain_lock);
406 hlist_for_each_entry(q, &hb->chain, list) {
407 if (q->net == nf && f->match(q, key)) {
408 atomic_inc(&q->refcnt);
409 spin_unlock(&hb->chain_lock);
410 return q;
411 }
412 depth++;
413 }
414 spin_unlock(&hb->chain_lock);
415
416 if (depth <= INETFRAGS_MAXDEPTH)
417 return inet_frag_create(nf, f, key);
418
419 if (inet_frag_may_rebuild(f)) {
420 if (!f->rebuild)
421 f->rebuild = true;
422 inet_frag_schedule_worker(f);
423 }
424
425 return ERR_PTR(-ENOBUFS);
426}
427EXPORT_SYMBOL(inet_frag_find);
428
429void inet_frag_maybe_warn_overflow(struct inet_frag_queue *q,
430 const char *prefix)
431{
432 static const char msg[] = "inet_frag_find: Fragment hash bucket"
433 " list length grew over limit " __stringify(INETFRAGS_MAXDEPTH)
434 ". Dropping fragment.\n";
435
436 if (PTR_ERR(q) == -ENOBUFS)
437 net_dbg_ratelimited("%s%s", prefix, msg);
438}
439EXPORT_SYMBOL(inet_frag_maybe_warn_overflow);