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 = file_inode(filp); 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 */ 124 125 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 (test_bit(UNIX_GC_CANDIDATE, &u->gc_flags)) { 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 (test_bit(UNIX_GC_MAYBE_CYCLE, &u->gc_flags)) 258 list_move_tail(&u->link, &gc_candidates); 259 } 260 261 static bool gc_in_progress; 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 __set_bit(UNIX_GC_CANDIDATE, &u->gc_flags); 319 __set_bit(UNIX_GC_MAYBE_CYCLE, &u->gc_flags); 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 __clear_bit(UNIX_GC_MAYBE_CYCLE, &u->gc_flags); 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 __clear_bit(UNIX_GC_CANDIDATE, &u->gc_flags); 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