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1/*
2 * NET3: Garbage Collector For AF_UNIX sockets
3 *
4 * Garbage Collector:
5 * Copyright (C) Barak A. Pearlmutter.
6 * Released under the GPL version 2 or later.
7 *
8 * Chopped about by Alan Cox 22/3/96 to make it fit the AF_UNIX socket problem.
9 * If it doesn't work blame me, it worked when Barak sent it.
10 *
11 * Assumptions:
12 *
13 * - object w/ a bit
14 * - free list
15 *
16 * Current optimizations:
17 *
18 * - explicit stack instead of recursion
19 * - tail recurse on first born instead of immediate push/pop
20 * - we gather the stuff that should not be killed into tree
21 * and stack is just a path from root to the current pointer.
22 *
23 * Future optimizations:
24 *
25 * - don't just push entire root set; process in place
26 *
27 * This program is free software; you can redistribute it and/or
28 * modify it under the terms of the GNU General Public License
29 * as published by the Free Software Foundation; either version
30 * 2 of the License, or (at your option) any later version.
31 *
32 * Fixes:
33 * Alan Cox 07 Sept 1997 Vmalloc internal stack as needed.
34 * Cope with changing max_files.
35 * Al Viro 11 Oct 1998
36 * Graph may have cycles. That is, we can send the descriptor
37 * of foo to bar and vice versa. Current code chokes on that.
38 * Fix: move SCM_RIGHTS ones into the separate list and then
39 * skb_free() them all instead of doing explicit fput's.
40 * Another problem: since fput() may block somebody may
41 * create a new unix_socket when we are in the middle of sweep
42 * phase. Fix: revert the logic wrt MARKED. Mark everything
43 * upon the beginning and unmark non-junk ones.
44 *
45 * [12 Oct 1998] AAARGH! New code purges all SCM_RIGHTS
46 * sent to connect()'ed but still not accept()'ed sockets.
47 * Fixed. Old code had slightly different problem here:
48 * extra fput() in situation when we passed the descriptor via
49 * such socket and closed it (descriptor). That would happen on
50 * each unix_gc() until the accept(). Since the struct file in
51 * question would go to the free list and might be reused...
52 * That might be the reason of random oopses on filp_close()
53 * in unrelated processes.
54 *
55 * AV 28 Feb 1999
56 * Kill the explicit allocation of stack. Now we keep the tree
57 * with root in dummy + pointer (gc_current) to one of the nodes.
58 * Stack is represented as path from gc_current to dummy. Unmark
59 * now means "add to tree". Push == "make it a son of gc_current".
60 * Pop == "move gc_current to parent". We keep only pointers to
61 * parents (->gc_tree).
62 * AV 1 Mar 1999
63 * Damn. Added missing check for ->dead in listen queues scanning.
64 *
65 * Miklos Szeredi 25 Jun 2007
66 * Reimplement with a cycle collecting algorithm. This should
67 * solve several problems with the previous code, like being racy
68 * wrt receive and holding up unrelated socket operations.
69 */
70
71#include <linux/kernel.h>
72#include <linux/string.h>
73#include <linux/socket.h>
74#include <linux/un.h>
75#include <linux/net.h>
76#include <linux/fs.h>
77#include <linux/skbuff.h>
78#include <linux/netdevice.h>
79#include <linux/file.h>
80#include <linux/proc_fs.h>
81#include <linux/mutex.h>
82#include <linux/wait.h>
83
84#include <net/sock.h>
85#include <net/af_unix.h>
86#include <net/scm.h>
87#include <net/tcp_states.h>
88
89/* Internal data structures and random procedures: */
90
91static LIST_HEAD(gc_inflight_list);
92static LIST_HEAD(gc_candidates);
93static DEFINE_SPINLOCK(unix_gc_lock);
94static DECLARE_WAIT_QUEUE_HEAD(unix_gc_wait);
95
96unsigned int unix_tot_inflight;
97
98struct sock *unix_get_socket(struct file *filp)
99{
100 struct sock *u_sock = NULL;
101 struct inode *inode = file_inode(filp);
102
103 /* Socket ? */
104 if (S_ISSOCK(inode->i_mode) && !(filp->f_mode & FMODE_PATH)) {
105 struct socket *sock = SOCKET_I(inode);
106 struct sock *s = sock->sk;
107
108 /* PF_UNIX ? */
109 if (s && sock->ops && sock->ops->family == PF_UNIX)
110 u_sock = s;
111 }
112 return u_sock;
113}
114
115/* Keep the number of times in flight count for the file
116 * descriptor if it is for an AF_UNIX socket.
117 */
118
119void unix_inflight(struct user_struct *user, struct file *fp)
120{
121 struct sock *s = unix_get_socket(fp);
122
123 spin_lock(&unix_gc_lock);
124
125 if (s) {
126 struct unix_sock *u = unix_sk(s);
127
128 if (atomic_long_inc_return(&u->inflight) == 1) {
129 BUG_ON(!list_empty(&u->link));
130 list_add_tail(&u->link, &gc_inflight_list);
131 } else {
132 BUG_ON(list_empty(&u->link));
133 }
134 unix_tot_inflight++;
135 }
136 user->unix_inflight++;
137 spin_unlock(&unix_gc_lock);
138}
139
140void unix_notinflight(struct user_struct *user, struct file *fp)
141{
142 struct sock *s = unix_get_socket(fp);
143
144 spin_lock(&unix_gc_lock);
145
146 if (s) {
147 struct unix_sock *u = unix_sk(s);
148
149 BUG_ON(!atomic_long_read(&u->inflight));
150 BUG_ON(list_empty(&u->link));
151
152 if (atomic_long_dec_and_test(&u->inflight))
153 list_del_init(&u->link);
154 unix_tot_inflight--;
155 }
156 user->unix_inflight--;
157 spin_unlock(&unix_gc_lock);
158}
159
160static void scan_inflight(struct sock *x, void (*func)(struct unix_sock *),
161 struct sk_buff_head *hitlist)
162{
163 struct sk_buff *skb;
164 struct sk_buff *next;
165
166 spin_lock(&x->sk_receive_queue.lock);
167 skb_queue_walk_safe(&x->sk_receive_queue, skb, next) {
168 /* Do we have file descriptors ? */
169 if (UNIXCB(skb).fp) {
170 bool hit = false;
171 /* Process the descriptors of this socket */
172 int nfd = UNIXCB(skb).fp->count;
173 struct file **fp = UNIXCB(skb).fp->fp;
174
175 while (nfd--) {
176 /* Get the socket the fd matches if it indeed does so */
177 struct sock *sk = unix_get_socket(*fp++);
178
179 if (sk) {
180 struct unix_sock *u = unix_sk(sk);
181
182 /* Ignore non-candidates, they could
183 * have been added to the queues after
184 * starting the garbage collection
185 */
186 if (test_bit(UNIX_GC_CANDIDATE, &u->gc_flags)) {
187 hit = true;
188
189 func(u);
190 }
191 }
192 }
193 if (hit && hitlist != NULL) {
194 __skb_unlink(skb, &x->sk_receive_queue);
195 __skb_queue_tail(hitlist, skb);
196 }
197 }
198 }
199 spin_unlock(&x->sk_receive_queue.lock);
200}
201
202static void scan_children(struct sock *x, void (*func)(struct unix_sock *),
203 struct sk_buff_head *hitlist)
204{
205 if (x->sk_state != TCP_LISTEN) {
206 scan_inflight(x, func, hitlist);
207 } else {
208 struct sk_buff *skb;
209 struct sk_buff *next;
210 struct unix_sock *u;
211 LIST_HEAD(embryos);
212
213 /* For a listening socket collect the queued embryos
214 * and perform a scan on them as well.
215 */
216 spin_lock(&x->sk_receive_queue.lock);
217 skb_queue_walk_safe(&x->sk_receive_queue, skb, next) {
218 u = unix_sk(skb->sk);
219
220 /* An embryo cannot be in-flight, so it's safe
221 * to use the list link.
222 */
223 BUG_ON(!list_empty(&u->link));
224 list_add_tail(&u->link, &embryos);
225 }
226 spin_unlock(&x->sk_receive_queue.lock);
227
228 while (!list_empty(&embryos)) {
229 u = list_entry(embryos.next, struct unix_sock, link);
230 scan_inflight(&u->sk, func, hitlist);
231 list_del_init(&u->link);
232 }
233 }
234}
235
236static void dec_inflight(struct unix_sock *usk)
237{
238 atomic_long_dec(&usk->inflight);
239}
240
241static void inc_inflight(struct unix_sock *usk)
242{
243 atomic_long_inc(&usk->inflight);
244}
245
246static void inc_inflight_move_tail(struct unix_sock *u)
247{
248 atomic_long_inc(&u->inflight);
249 /* If this still might be part of a cycle, move it to the end
250 * of the list, so that it's checked even if it was already
251 * passed over
252 */
253 if (test_bit(UNIX_GC_MAYBE_CYCLE, &u->gc_flags))
254 list_move_tail(&u->link, &gc_candidates);
255}
256
257static bool gc_in_progress;
258#define UNIX_INFLIGHT_TRIGGER_GC 16000
259
260void wait_for_unix_gc(void)
261{
262 /* If number of inflight sockets is insane,
263 * force a garbage collect right now.
264 */
265 if (unix_tot_inflight > UNIX_INFLIGHT_TRIGGER_GC && !gc_in_progress)
266 unix_gc();
267 wait_event(unix_gc_wait, gc_in_progress == false);
268}
269
270/* The external entry point: unix_gc() */
271void unix_gc(void)
272{
273 struct unix_sock *u;
274 struct unix_sock *next;
275 struct sk_buff_head hitlist;
276 struct list_head cursor;
277 LIST_HEAD(not_cycle_list);
278
279 spin_lock(&unix_gc_lock);
280
281 /* Avoid a recursive GC. */
282 if (gc_in_progress)
283 goto out;
284
285 gc_in_progress = true;
286 /* First, select candidates for garbage collection. Only
287 * in-flight sockets are considered, and from those only ones
288 * which don't have any external reference.
289 *
290 * Holding unix_gc_lock will protect these candidates from
291 * being detached, and hence from gaining an external
292 * reference. Since there are no possible receivers, all
293 * buffers currently on the candidates' queues stay there
294 * during the garbage collection.
295 *
296 * We also know that no new candidate can be added onto the
297 * receive queues. Other, non candidate sockets _can_ be
298 * added to queue, so we must make sure only to touch
299 * candidates.
300 */
301 list_for_each_entry_safe(u, next, &gc_inflight_list, link) {
302 long total_refs;
303 long inflight_refs;
304
305 total_refs = file_count(u->sk.sk_socket->file);
306 inflight_refs = atomic_long_read(&u->inflight);
307
308 BUG_ON(inflight_refs < 1);
309 BUG_ON(total_refs < inflight_refs);
310 if (total_refs == inflight_refs) {
311 list_move_tail(&u->link, &gc_candidates);
312 __set_bit(UNIX_GC_CANDIDATE, &u->gc_flags);
313 __set_bit(UNIX_GC_MAYBE_CYCLE, &u->gc_flags);
314 }
315 }
316
317 /* Now remove all internal in-flight reference to children of
318 * the candidates.
319 */
320 list_for_each_entry(u, &gc_candidates, link)
321 scan_children(&u->sk, dec_inflight, NULL);
322
323 /* Restore the references for children of all candidates,
324 * which have remaining references. Do this recursively, so
325 * only those remain, which form cyclic references.
326 *
327 * Use a "cursor" link, to make the list traversal safe, even
328 * though elements might be moved about.
329 */
330 list_add(&cursor, &gc_candidates);
331 while (cursor.next != &gc_candidates) {
332 u = list_entry(cursor.next, struct unix_sock, link);
333
334 /* Move cursor to after the current position. */
335 list_move(&cursor, &u->link);
336
337 if (atomic_long_read(&u->inflight) > 0) {
338 list_move_tail(&u->link, ¬_cycle_list);
339 __clear_bit(UNIX_GC_MAYBE_CYCLE, &u->gc_flags);
340 scan_children(&u->sk, inc_inflight_move_tail, NULL);
341 }
342 }
343 list_del(&cursor);
344
345 /* Now gc_candidates contains only garbage. Restore original
346 * inflight counters for these as well, and remove the skbuffs
347 * which are creating the cycle(s).
348 */
349 skb_queue_head_init(&hitlist);
350 list_for_each_entry(u, &gc_candidates, link)
351 scan_children(&u->sk, inc_inflight, &hitlist);
352
353 /* not_cycle_list contains those sockets which do not make up a
354 * cycle. Restore these to the inflight list.
355 */
356 while (!list_empty(¬_cycle_list)) {
357 u = list_entry(not_cycle_list.next, struct unix_sock, link);
358 __clear_bit(UNIX_GC_CANDIDATE, &u->gc_flags);
359 list_move_tail(&u->link, &gc_inflight_list);
360 }
361
362 spin_unlock(&unix_gc_lock);
363
364 /* Here we are. Hitlist is filled. Die. */
365 __skb_queue_purge(&hitlist);
366
367 spin_lock(&unix_gc_lock);
368
369 /* All candidates should have been detached by now. */
370 BUG_ON(!list_empty(&gc_candidates));
371 gc_in_progress = false;
372 wake_up(&unix_gc_wait);
373
374 out:
375 spin_unlock(&unix_gc_lock);
376}
1/*
2 * NET3: Garbage Collector For AF_UNIX sockets
3 *
4 * Garbage Collector:
5 * Copyright (C) Barak A. Pearlmutter.
6 * Released under the GPL version 2 or later.
7 *
8 * Chopped about by Alan Cox 22/3/96 to make it fit the AF_UNIX socket problem.
9 * If it doesn't work blame me, it worked when Barak sent it.
10 *
11 * Assumptions:
12 *
13 * - object w/ a bit
14 * - free list
15 *
16 * Current optimizations:
17 *
18 * - explicit stack instead of recursion
19 * - tail recurse on first born instead of immediate push/pop
20 * - we gather the stuff that should not be killed into tree
21 * and stack is just a path from root to the current pointer.
22 *
23 * Future optimizations:
24 *
25 * - don't just push entire root set; process in place
26 *
27 * This program is free software; you can redistribute it and/or
28 * modify it under the terms of the GNU General Public License
29 * as published by the Free Software Foundation; either version
30 * 2 of the License, or (at your option) any later version.
31 *
32 * Fixes:
33 * Alan Cox 07 Sept 1997 Vmalloc internal stack as needed.
34 * Cope with changing max_files.
35 * Al Viro 11 Oct 1998
36 * Graph may have cycles. That is, we can send the descriptor
37 * of foo to bar and vice versa. Current code chokes on that.
38 * Fix: move SCM_RIGHTS ones into the separate list and then
39 * skb_free() them all instead of doing explicit fput's.
40 * Another problem: since fput() may block somebody may
41 * create a new unix_socket when we are in the middle of sweep
42 * phase. Fix: revert the logic wrt MARKED. Mark everything
43 * upon the beginning and unmark non-junk ones.
44 *
45 * [12 Oct 1998] AAARGH! New code purges all SCM_RIGHTS
46 * sent to connect()'ed but still not accept()'ed sockets.
47 * Fixed. Old code had slightly different problem here:
48 * extra fput() in situation when we passed the descriptor via
49 * such socket and closed it (descriptor). That would happen on
50 * each unix_gc() until the accept(). Since the struct file in
51 * question would go to the free list and might be reused...
52 * That might be the reason of random oopses on filp_close()
53 * in unrelated processes.
54 *
55 * AV 28 Feb 1999
56 * Kill the explicit allocation of stack. Now we keep the tree
57 * with root in dummy + pointer (gc_current) to one of the nodes.
58 * Stack is represented as path from gc_current to dummy. Unmark
59 * now means "add to tree". Push == "make it a son of gc_current".
60 * Pop == "move gc_current to parent". We keep only pointers to
61 * parents (->gc_tree).
62 * AV 1 Mar 1999
63 * Damn. Added missing check for ->dead in listen queues scanning.
64 *
65 * Miklos Szeredi 25 Jun 2007
66 * Reimplement with a cycle collecting algorithm. This should
67 * solve several problems with the previous code, like being racy
68 * wrt receive and holding up unrelated socket operations.
69 */
70
71#include <linux/kernel.h>
72#include <linux/string.h>
73#include <linux/socket.h>
74#include <linux/un.h>
75#include <linux/net.h>
76#include <linux/fs.h>
77#include <linux/skbuff.h>
78#include <linux/netdevice.h>
79#include <linux/file.h>
80#include <linux/proc_fs.h>
81#include <linux/mutex.h>
82#include <linux/wait.h>
83
84#include <net/sock.h>
85#include <net/af_unix.h>
86#include <net/scm.h>
87#include <net/tcp_states.h>
88
89/* Internal data structures and random procedures: */
90
91static LIST_HEAD(gc_inflight_list);
92static LIST_HEAD(gc_candidates);
93static DEFINE_SPINLOCK(unix_gc_lock);
94static DECLARE_WAIT_QUEUE_HEAD(unix_gc_wait);
95
96unsigned int unix_tot_inflight;
97
98
99struct sock *unix_get_socket(struct file *filp)
100{
101 struct sock *u_sock = NULL;
102 struct inode *inode = filp->f_path.dentry->d_inode;
103
104 /*
105 * Socket ?
106 */
107 if (S_ISSOCK(inode->i_mode) && !(filp->f_mode & FMODE_PATH)) {
108 struct socket *sock = SOCKET_I(inode);
109 struct sock *s = sock->sk;
110
111 /*
112 * PF_UNIX ?
113 */
114 if (s && sock->ops && sock->ops->family == PF_UNIX)
115 u_sock = s;
116 }
117 return u_sock;
118}
119
120/*
121 * Keep the number of times in flight count for the file
122 * descriptor if it is for an AF_UNIX socket.
123 */
124
125void unix_inflight(struct file *fp)
126{
127 struct sock *s = unix_get_socket(fp);
128 if (s) {
129 struct unix_sock *u = unix_sk(s);
130 spin_lock(&unix_gc_lock);
131 if (atomic_long_inc_return(&u->inflight) == 1) {
132 BUG_ON(!list_empty(&u->link));
133 list_add_tail(&u->link, &gc_inflight_list);
134 } else {
135 BUG_ON(list_empty(&u->link));
136 }
137 unix_tot_inflight++;
138 spin_unlock(&unix_gc_lock);
139 }
140}
141
142void unix_notinflight(struct file *fp)
143{
144 struct sock *s = unix_get_socket(fp);
145 if (s) {
146 struct unix_sock *u = unix_sk(s);
147 spin_lock(&unix_gc_lock);
148 BUG_ON(list_empty(&u->link));
149 if (atomic_long_dec_and_test(&u->inflight))
150 list_del_init(&u->link);
151 unix_tot_inflight--;
152 spin_unlock(&unix_gc_lock);
153 }
154}
155
156static void scan_inflight(struct sock *x, void (*func)(struct unix_sock *),
157 struct sk_buff_head *hitlist)
158{
159 struct sk_buff *skb;
160 struct sk_buff *next;
161
162 spin_lock(&x->sk_receive_queue.lock);
163 skb_queue_walk_safe(&x->sk_receive_queue, skb, next) {
164 /*
165 * Do we have file descriptors ?
166 */
167 if (UNIXCB(skb).fp) {
168 bool hit = false;
169 /*
170 * Process the descriptors of this socket
171 */
172 int nfd = UNIXCB(skb).fp->count;
173 struct file **fp = UNIXCB(skb).fp->fp;
174 while (nfd--) {
175 /*
176 * Get the socket the fd matches
177 * if it indeed does so
178 */
179 struct sock *sk = unix_get_socket(*fp++);
180 if (sk) {
181 struct unix_sock *u = unix_sk(sk);
182
183 /*
184 * Ignore non-candidates, they could
185 * have been added to the queues after
186 * starting the garbage collection
187 */
188 if (u->gc_candidate) {
189 hit = true;
190 func(u);
191 }
192 }
193 }
194 if (hit && hitlist != NULL) {
195 __skb_unlink(skb, &x->sk_receive_queue);
196 __skb_queue_tail(hitlist, skb);
197 }
198 }
199 }
200 spin_unlock(&x->sk_receive_queue.lock);
201}
202
203static void scan_children(struct sock *x, void (*func)(struct unix_sock *),
204 struct sk_buff_head *hitlist)
205{
206 if (x->sk_state != TCP_LISTEN)
207 scan_inflight(x, func, hitlist);
208 else {
209 struct sk_buff *skb;
210 struct sk_buff *next;
211 struct unix_sock *u;
212 LIST_HEAD(embryos);
213
214 /*
215 * For a listening socket collect the queued embryos
216 * and perform a scan on them as well.
217 */
218 spin_lock(&x->sk_receive_queue.lock);
219 skb_queue_walk_safe(&x->sk_receive_queue, skb, next) {
220 u = unix_sk(skb->sk);
221
222 /*
223 * An embryo cannot be in-flight, so it's safe
224 * to use the list link.
225 */
226 BUG_ON(!list_empty(&u->link));
227 list_add_tail(&u->link, &embryos);
228 }
229 spin_unlock(&x->sk_receive_queue.lock);
230
231 while (!list_empty(&embryos)) {
232 u = list_entry(embryos.next, struct unix_sock, link);
233 scan_inflight(&u->sk, func, hitlist);
234 list_del_init(&u->link);
235 }
236 }
237}
238
239static void dec_inflight(struct unix_sock *usk)
240{
241 atomic_long_dec(&usk->inflight);
242}
243
244static void inc_inflight(struct unix_sock *usk)
245{
246 atomic_long_inc(&usk->inflight);
247}
248
249static void inc_inflight_move_tail(struct unix_sock *u)
250{
251 atomic_long_inc(&u->inflight);
252 /*
253 * If this still might be part of a cycle, move it to the end
254 * of the list, so that it's checked even if it was already
255 * passed over
256 */
257 if (u->gc_maybe_cycle)
258 list_move_tail(&u->link, &gc_candidates);
259}
260
261static bool gc_in_progress = false;
262#define UNIX_INFLIGHT_TRIGGER_GC 16000
263
264void wait_for_unix_gc(void)
265{
266 /*
267 * If number of inflight sockets is insane,
268 * force a garbage collect right now.
269 */
270 if (unix_tot_inflight > UNIX_INFLIGHT_TRIGGER_GC && !gc_in_progress)
271 unix_gc();
272 wait_event(unix_gc_wait, gc_in_progress == false);
273}
274
275/* The external entry point: unix_gc() */
276void unix_gc(void)
277{
278 struct unix_sock *u;
279 struct unix_sock *next;
280 struct sk_buff_head hitlist;
281 struct list_head cursor;
282 LIST_HEAD(not_cycle_list);
283
284 spin_lock(&unix_gc_lock);
285
286 /* Avoid a recursive GC. */
287 if (gc_in_progress)
288 goto out;
289
290 gc_in_progress = true;
291 /*
292 * First, select candidates for garbage collection. Only
293 * in-flight sockets are considered, and from those only ones
294 * which don't have any external reference.
295 *
296 * Holding unix_gc_lock will protect these candidates from
297 * being detached, and hence from gaining an external
298 * reference. Since there are no possible receivers, all
299 * buffers currently on the candidates' queues stay there
300 * during the garbage collection.
301 *
302 * We also know that no new candidate can be added onto the
303 * receive queues. Other, non candidate sockets _can_ be
304 * added to queue, so we must make sure only to touch
305 * candidates.
306 */
307 list_for_each_entry_safe(u, next, &gc_inflight_list, link) {
308 long total_refs;
309 long inflight_refs;
310
311 total_refs = file_count(u->sk.sk_socket->file);
312 inflight_refs = atomic_long_read(&u->inflight);
313
314 BUG_ON(inflight_refs < 1);
315 BUG_ON(total_refs < inflight_refs);
316 if (total_refs == inflight_refs) {
317 list_move_tail(&u->link, &gc_candidates);
318 u->gc_candidate = 1;
319 u->gc_maybe_cycle = 1;
320 }
321 }
322
323 /*
324 * Now remove all internal in-flight reference to children of
325 * the candidates.
326 */
327 list_for_each_entry(u, &gc_candidates, link)
328 scan_children(&u->sk, dec_inflight, NULL);
329
330 /*
331 * Restore the references for children of all candidates,
332 * which have remaining references. Do this recursively, so
333 * only those remain, which form cyclic references.
334 *
335 * Use a "cursor" link, to make the list traversal safe, even
336 * though elements might be moved about.
337 */
338 list_add(&cursor, &gc_candidates);
339 while (cursor.next != &gc_candidates) {
340 u = list_entry(cursor.next, struct unix_sock, link);
341
342 /* Move cursor to after the current position. */
343 list_move(&cursor, &u->link);
344
345 if (atomic_long_read(&u->inflight) > 0) {
346 list_move_tail(&u->link, ¬_cycle_list);
347 u->gc_maybe_cycle = 0;
348 scan_children(&u->sk, inc_inflight_move_tail, NULL);
349 }
350 }
351 list_del(&cursor);
352
353 /*
354 * not_cycle_list contains those sockets which do not make up a
355 * cycle. Restore these to the inflight list.
356 */
357 while (!list_empty(¬_cycle_list)) {
358 u = list_entry(not_cycle_list.next, struct unix_sock, link);
359 u->gc_candidate = 0;
360 list_move_tail(&u->link, &gc_inflight_list);
361 }
362
363 /*
364 * Now gc_candidates contains only garbage. Restore original
365 * inflight counters for these as well, and remove the skbuffs
366 * which are creating the cycle(s).
367 */
368 skb_queue_head_init(&hitlist);
369 list_for_each_entry(u, &gc_candidates, link)
370 scan_children(&u->sk, inc_inflight, &hitlist);
371
372 spin_unlock(&unix_gc_lock);
373
374 /* Here we are. Hitlist is filled. Die. */
375 __skb_queue_purge(&hitlist);
376
377 spin_lock(&unix_gc_lock);
378
379 /* All candidates should have been detached by now. */
380 BUG_ON(!list_empty(&gc_candidates));
381 gc_in_progress = false;
382 wake_up(&unix_gc_wait);
383
384 out:
385 spin_unlock(&unix_gc_lock);
386}