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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 | |
91 | static LIST_HEAD(gc_inflight_list); |
92 | static LIST_HEAD(gc_candidates); |
93 | static DEFINE_SPINLOCK(unix_gc_lock); |
94 | static DECLARE_WAIT_QUEUE_HEAD(unix_gc_wait); |
95 | |
96 | unsigned int unix_tot_inflight; |
97 | |
98 | |
99 | struct 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)) { |
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 | |
125 | void 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 | |
142 | void 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 | |
156 | static 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 | |
203 | static 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 | |
239 | static void dec_inflight(struct unix_sock *usk) |
240 | { |
241 | atomic_long_dec(&usk->inflight); |
242 | } |
243 | |
244 | static void inc_inflight(struct unix_sock *usk) |
245 | { |
246 | atomic_long_inc(&usk->inflight); |
247 | } |
248 | |
249 | static 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 | |
261 | static bool gc_in_progress = false; |
262 | #define UNIX_INFLIGHT_TRIGGER_GC 16000 |
263 | |
264 | void 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() */ |
276 | void 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 | } |
387 |
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