projects/linux·blob v2.6.14 · refs

834 lines · 18.3 KiB

1/*
2 * linux/ipc/msg.c
3 * Copyright (C) 1992 Krishna Balasubramanian
4 *
5 * Removed all the remaining kerneld mess
6 * Catch the -EFAULT stuff properly
7 * Use GFP_KERNEL for messages as in 1.2
8 * Fixed up the unchecked user space derefs
9 * Copyright (C) 1998 Alan Cox & Andi Kleen
10 *
11 * /proc/sysvipc/msg support (c) 1999 Dragos Acostachioaie <[email protected]>
12 *
13 * mostly rewritten, threaded and wake-one semantics added
14 * MSGMAX limit removed, sysctl's added
15 * (c) 1999 Manfred Spraul <[email protected]>
16 */
17
18#include <linux/config.h>
19#include <linux/slab.h>
20#include <linux/msg.h>
21#include <linux/spinlock.h>
22#include <linux/init.h>
23#include <linux/proc_fs.h>
24#include <linux/list.h>
25#include <linux/security.h>
26#include <linux/sched.h>
27#include <linux/syscalls.h>
28#include <linux/audit.h>
29#include <linux/seq_file.h>
30#include <asm/current.h>
31#include <asm/uaccess.h>
32#include "util.h"
33
34/* sysctl: */
35int msg_ctlmax = MSGMAX;
36int msg_ctlmnb = MSGMNB;
37int msg_ctlmni = MSGMNI;
38
39/* one msg_receiver structure for each sleeping receiver */
40struct msg_receiver {
41 struct list_head r_list;
42 struct task_struct* r_tsk;
43
44 int r_mode;
45 long r_msgtype;
46 long r_maxsize;
47
48 struct msg_msg* volatile r_msg;
49};
50
51/* one msg_sender for each sleeping sender */
52struct msg_sender {
53 struct list_head list;
54 struct task_struct* tsk;
55};
56
57#define SEARCH_ANY 1
58#define SEARCH_EQUAL 2
59#define SEARCH_NOTEQUAL 3
60#define SEARCH_LESSEQUAL 4
61
62static atomic_t msg_bytes = ATOMIC_INIT(0);
63static atomic_t msg_hdrs = ATOMIC_INIT(0);
64
65static struct ipc_ids msg_ids;
66
67#define msg_lock(id) ((struct msg_queue*)ipc_lock(&msg_ids,id))
68#define msg_unlock(msq) ipc_unlock(&(msq)->q_perm)
69#define msg_rmid(id) ((struct msg_queue*)ipc_rmid(&msg_ids,id))
70#define msg_checkid(msq, msgid) \
71 ipc_checkid(&msg_ids,&msq->q_perm,msgid)
72#define msg_buildid(id, seq) \
73 ipc_buildid(&msg_ids, id, seq)
74
75static void freeque (struct msg_queue *msq, int id);
76static int newque (key_t key, int msgflg);
77#ifdef CONFIG_PROC_FS
78static int sysvipc_msg_proc_show(struct seq_file *s, void *it);
79#endif
80
81void __init msg_init (void)
82{
83 ipc_init_ids(&msg_ids,msg_ctlmni);
84 ipc_init_proc_interface("sysvipc/msg",
85 " key msqid perms cbytes qnum lspid lrpid uid gid cuid cgid stime rtime ctime\n",
86 &msg_ids,
87 sysvipc_msg_proc_show);
88}
89
90static int newque (key_t key, int msgflg)
91{
92 int id;
93 int retval;
94 struct msg_queue *msq;
95
96 msq = ipc_rcu_alloc(sizeof(*msq));
97 if (!msq)
98 return -ENOMEM;
99
100 msq->q_perm.mode = (msgflg & S_IRWXUGO);
101 msq->q_perm.key = key;
102
103 msq->q_perm.security = NULL;
104 retval = security_msg_queue_alloc(msq);
105 if (retval) {
106 ipc_rcu_putref(msq);
107 return retval;
108 }
109
110 id = ipc_addid(&msg_ids, &msq->q_perm, msg_ctlmni);
111 if(id == -1) {
112 security_msg_queue_free(msq);
113 ipc_rcu_putref(msq);
114 return -ENOSPC;
115 }
116
117 msq->q_id = msg_buildid(id,msq->q_perm.seq);
118 msq->q_stime = msq->q_rtime = 0;
119 msq->q_ctime = get_seconds();
120 msq->q_cbytes = msq->q_qnum = 0;
121 msq->q_qbytes = msg_ctlmnb;
122 msq->q_lspid = msq->q_lrpid = 0;
123 INIT_LIST_HEAD(&msq->q_messages);
124 INIT_LIST_HEAD(&msq->q_receivers);
125 INIT_LIST_HEAD(&msq->q_senders);
126 msg_unlock(msq);
127
128 return msq->q_id;
129}
130
131static inline void ss_add(struct msg_queue* msq, struct msg_sender* mss)
132{
133 mss->tsk=current;
134 current->state=TASK_INTERRUPTIBLE;
135 list_add_tail(&mss->list,&msq->q_senders);
136}
137
138static inline void ss_del(struct msg_sender* mss)
139{
140 if(mss->list.next != NULL)
141 list_del(&mss->list);
142}
143
144static void ss_wakeup(struct list_head* h, int kill)
145{
146 struct list_head *tmp;
147
148 tmp = h->next;
149 while (tmp != h) {
150 struct msg_sender* mss;
151
152 mss = list_entry(tmp,struct msg_sender,list);
153 tmp = tmp->next;
154 if(kill)
155 mss->list.next=NULL;
156 wake_up_process(mss->tsk);
157 }
158}
159
160static void expunge_all(struct msg_queue* msq, int res)
161{
162 struct list_head *tmp;
163
164 tmp = msq->q_receivers.next;
165 while (tmp != &msq->q_receivers) {
166 struct msg_receiver* msr;
167
168 msr = list_entry(tmp,struct msg_receiver,r_list);
169 tmp = tmp->next;
170 msr->r_msg = NULL;
171 wake_up_process(msr->r_tsk);
172 smp_mb();
173 msr->r_msg = ERR_PTR(res);
174 }
175}
176/*
177 * freeque() wakes up waiters on the sender and receiver waiting queue,
178 * removes the message queue from message queue ID
179 * array, and cleans up all the messages associated with this queue.
180 *
181 * msg_ids.sem and the spinlock for this message queue is hold
182 * before freeque() is called. msg_ids.sem remains locked on exit.
183 */
184static void freeque (struct msg_queue *msq, int id)
185{
186 struct list_head *tmp;
187
188 expunge_all(msq,-EIDRM);
189 ss_wakeup(&msq->q_senders,1);
190 msq = msg_rmid(id);
191 msg_unlock(msq);
192
193 tmp = msq->q_messages.next;
194 while(tmp != &msq->q_messages) {
195 struct msg_msg* msg = list_entry(tmp,struct msg_msg,m_list);
196 tmp = tmp->next;
197 atomic_dec(&msg_hdrs);
198 free_msg(msg);
199 }
200 atomic_sub(msq->q_cbytes, &msg_bytes);
201 security_msg_queue_free(msq);
202 ipc_rcu_putref(msq);
203}
204
205asmlinkage long sys_msgget (key_t key, int msgflg)
206{
207 int id, ret = -EPERM;
208 struct msg_queue *msq;
209
210 down(&msg_ids.sem);
211 if (key == IPC_PRIVATE)
212 ret = newque(key, msgflg);
213 else if ((id = ipc_findkey(&msg_ids, key)) == -1) { /* key not used */
214 if (!(msgflg & IPC_CREAT))
215 ret = -ENOENT;
216 else
217 ret = newque(key, msgflg);
218 } else if (msgflg & IPC_CREAT && msgflg & IPC_EXCL) {
219 ret = -EEXIST;
220 } else {
221 msq = msg_lock(id);
222 if(msq==NULL)
223 BUG();
224 if (ipcperms(&msq->q_perm, msgflg))
225 ret = -EACCES;
226 else {
227 int qid = msg_buildid(id, msq->q_perm.seq);
228 ret = security_msg_queue_associate(msq, msgflg);
229 if (!ret)
230 ret = qid;
231 }
232 msg_unlock(msq);
233 }
234 up(&msg_ids.sem);
235 return ret;
236}
237
238static inline unsigned long copy_msqid_to_user(void __user *buf, struct msqid64_ds *in, int version)
239{
240 switch(version) {
241 case IPC_64:
242 return copy_to_user (buf, in, sizeof(*in));
243 case IPC_OLD:
244 {
245 struct msqid_ds out;
246
247 memset(&out,0,sizeof(out));
248
249 ipc64_perm_to_ipc_perm(&in->msg_perm, &out.msg_perm);
250
251 out.msg_stime = in->msg_stime;
252 out.msg_rtime = in->msg_rtime;
253 out.msg_ctime = in->msg_ctime;
254
255 if(in->msg_cbytes > USHRT_MAX)
256 out.msg_cbytes = USHRT_MAX;
257 else
258 out.msg_cbytes = in->msg_cbytes;
259 out.msg_lcbytes = in->msg_cbytes;
260
261 if(in->msg_qnum > USHRT_MAX)
262 out.msg_qnum = USHRT_MAX;
263 else
264 out.msg_qnum = in->msg_qnum;
265
266 if(in->msg_qbytes > USHRT_MAX)
267 out.msg_qbytes = USHRT_MAX;
268 else
269 out.msg_qbytes = in->msg_qbytes;
270 out.msg_lqbytes = in->msg_qbytes;
271
272 out.msg_lspid = in->msg_lspid;
273 out.msg_lrpid = in->msg_lrpid;
274
275 return copy_to_user (buf, &out, sizeof(out));
276 }
277 default:
278 return -EINVAL;
279 }
280}
281
282struct msq_setbuf {
283 unsigned long qbytes;
284 uid_t uid;
285 gid_t gid;
286 mode_t mode;
287};
288
289static inline unsigned long copy_msqid_from_user(struct msq_setbuf *out, void __user *buf, int version)
290{
291 switch(version) {
292 case IPC_64:
293 {
294 struct msqid64_ds tbuf;
295
296 if (copy_from_user (&tbuf, buf, sizeof (tbuf)))
297 return -EFAULT;
298
299 out->qbytes = tbuf.msg_qbytes;
300 out->uid = tbuf.msg_perm.uid;
301 out->gid = tbuf.msg_perm.gid;
302 out->mode = tbuf.msg_perm.mode;
303
304 return 0;
305 }
306 case IPC_OLD:
307 {
308 struct msqid_ds tbuf_old;
309
310 if (copy_from_user (&tbuf_old, buf, sizeof (tbuf_old)))
311 return -EFAULT;
312
313 out->uid = tbuf_old.msg_perm.uid;
314 out->gid = tbuf_old.msg_perm.gid;
315 out->mode = tbuf_old.msg_perm.mode;
316
317 if(tbuf_old.msg_qbytes == 0)
318 out->qbytes = tbuf_old.msg_lqbytes;
319 else
320 out->qbytes = tbuf_old.msg_qbytes;
321
322 return 0;
323 }
324 default:
325 return -EINVAL;
326 }
327}
328
329asmlinkage long sys_msgctl (int msqid, int cmd, struct msqid_ds __user *buf)
330{
331 int err, version;
332 struct msg_queue *msq;
333 struct msq_setbuf setbuf;
334 struct kern_ipc_perm *ipcp;
335
336 if (msqid < 0 || cmd < 0)
337 return -EINVAL;
338
339 version = ipc_parse_version(&cmd);
340
341 switch (cmd) {
342 case IPC_INFO:
343 case MSG_INFO:
344 {
345 struct msginfo msginfo;
346 int max_id;
347 if (!buf)
348 return -EFAULT;
349 /* We must not return kernel stack data.
350 * due to padding, it's not enough
351 * to set all member fields.
352 */
353
354 err = security_msg_queue_msgctl(NULL, cmd);
355 if (err)
356 return err;
357
358 memset(&msginfo,0,sizeof(msginfo));
359 msginfo.msgmni = msg_ctlmni;
360 msginfo.msgmax = msg_ctlmax;
361 msginfo.msgmnb = msg_ctlmnb;
362 msginfo.msgssz = MSGSSZ;
363 msginfo.msgseg = MSGSEG;
364 down(&msg_ids.sem);
365 if (cmd == MSG_INFO) {
366 msginfo.msgpool = msg_ids.in_use;
367 msginfo.msgmap = atomic_read(&msg_hdrs);
368 msginfo.msgtql = atomic_read(&msg_bytes);
369 } else {
370 msginfo.msgmap = MSGMAP;
371 msginfo.msgpool = MSGPOOL;
372 msginfo.msgtql = MSGTQL;
373 }
374 max_id = msg_ids.max_id;
375 up(&msg_ids.sem);
376 if (copy_to_user (buf, &msginfo, sizeof(struct msginfo)))
377 return -EFAULT;
378 return (max_id < 0) ? 0: max_id;
379 }
380 case MSG_STAT:
381 case IPC_STAT:
382 {
383 struct msqid64_ds tbuf;
384 int success_return;
385 if (!buf)
386 return -EFAULT;
387 if(cmd == MSG_STAT && msqid >= msg_ids.entries->size)
388 return -EINVAL;
389
390 memset(&tbuf,0,sizeof(tbuf));
391
392 msq = msg_lock(msqid);
393 if (msq == NULL)
394 return -EINVAL;
395
396 if(cmd == MSG_STAT) {
397 success_return = msg_buildid(msqid, msq->q_perm.seq);
398 } else {
399 err = -EIDRM;
400 if (msg_checkid(msq,msqid))
401 goto out_unlock;
402 success_return = 0;
403 }
404 err = -EACCES;
405 if (ipcperms (&msq->q_perm, S_IRUGO))
406 goto out_unlock;
407
408 err = security_msg_queue_msgctl(msq, cmd);
409 if (err)
410 goto out_unlock;
411
412 kernel_to_ipc64_perm(&msq->q_perm, &tbuf.msg_perm);
413 tbuf.msg_stime = msq->q_stime;
414 tbuf.msg_rtime = msq->q_rtime;
415 tbuf.msg_ctime = msq->q_ctime;
416 tbuf.msg_cbytes = msq->q_cbytes;
417 tbuf.msg_qnum = msq->q_qnum;
418 tbuf.msg_qbytes = msq->q_qbytes;
419 tbuf.msg_lspid = msq->q_lspid;
420 tbuf.msg_lrpid = msq->q_lrpid;
421 msg_unlock(msq);
422 if (copy_msqid_to_user(buf, &tbuf, version))
423 return -EFAULT;
424 return success_return;
425 }
426 case IPC_SET:
427 if (!buf)
428 return -EFAULT;
429 if (copy_msqid_from_user (&setbuf, buf, version))
430 return -EFAULT;
431 if ((err = audit_ipc_perms(setbuf.qbytes, setbuf.uid, setbuf.gid, setbuf.mode)))
432 return err;
433 break;
434 case IPC_RMID:
435 break;
436 default:
437 return -EINVAL;
438 }
439
440 down(&msg_ids.sem);
441 msq = msg_lock(msqid);
442 err=-EINVAL;
443 if (msq == NULL)
444 goto out_up;
445
446 err = -EIDRM;
447 if (msg_checkid(msq,msqid))
448 goto out_unlock_up;
449 ipcp = &msq->q_perm;
450 err = -EPERM;
451 if (current->euid != ipcp->cuid &&
452 current->euid != ipcp->uid && !capable(CAP_SYS_ADMIN))
453 /* We _could_ check for CAP_CHOWN above, but we don't */
454 goto out_unlock_up;
455
456 err = security_msg_queue_msgctl(msq, cmd);
457 if (err)
458 goto out_unlock_up;
459
460 switch (cmd) {
461 case IPC_SET:
462 {
463 err = -EPERM;
464 if (setbuf.qbytes > msg_ctlmnb && !capable(CAP_SYS_RESOURCE))
465 goto out_unlock_up;
466
467 msq->q_qbytes = setbuf.qbytes;
468
469 ipcp->uid = setbuf.uid;
470 ipcp->gid = setbuf.gid;
471 ipcp->mode = (ipcp->mode & ~S_IRWXUGO) |
472 (S_IRWXUGO & setbuf.mode);
473 msq->q_ctime = get_seconds();
474 /* sleeping receivers might be excluded by
475 * stricter permissions.
476 */
477 expunge_all(msq,-EAGAIN);
478 /* sleeping senders might be able to send
479 * due to a larger queue size.
480 */
481 ss_wakeup(&msq->q_senders,0);
482 msg_unlock(msq);
483 break;
484 }
485 case IPC_RMID:
486 freeque (msq, msqid);
487 break;
488 }
489 err = 0;
490out_up:
491 up(&msg_ids.sem);
492 return err;
493out_unlock_up:
494 msg_unlock(msq);
495 goto out_up;
496out_unlock:
497 msg_unlock(msq);
498 return err;
499}
500
501static int testmsg(struct msg_msg* msg,long type,int mode)
502{
503 switch(mode)
504 {
505 case SEARCH_ANY:
506 return 1;
507 case SEARCH_LESSEQUAL:
508 if(msg->m_type <=type)
509 return 1;
510 break;
511 case SEARCH_EQUAL:
512 if(msg->m_type == type)
513 return 1;
514 break;
515 case SEARCH_NOTEQUAL:
516 if(msg->m_type != type)
517 return 1;
518 break;
519 }
520 return 0;
521}
522
523static inline int pipelined_send(struct msg_queue* msq, struct msg_msg* msg)
524{
525 struct list_head* tmp;
526
527 tmp = msq->q_receivers.next;
528 while (tmp != &msq->q_receivers) {
529 struct msg_receiver* msr;
530 msr = list_entry(tmp,struct msg_receiver,r_list);
531 tmp = tmp->next;
532 if(testmsg(msg,msr->r_msgtype,msr->r_mode) &&
533 !security_msg_queue_msgrcv(msq, msg, msr->r_tsk, msr->r_msgtype, msr->r_mode)) {
534 list_del(&msr->r_list);
535 if(msr->r_maxsize < msg->m_ts) {
536 msr->r_msg = NULL;
537 wake_up_process(msr->r_tsk);
538 smp_mb();
539 msr->r_msg = ERR_PTR(-E2BIG);
540 } else {
541 msr->r_msg = NULL;
542 msq->q_lrpid = msr->r_tsk->pid;
543 msq->q_rtime = get_seconds();
544 wake_up_process(msr->r_tsk);
545 smp_mb();
546 msr->r_msg = msg;
547 return 1;
548 }
549 }
550 }
551 return 0;
552}
553
554asmlinkage long sys_msgsnd (int msqid, struct msgbuf __user *msgp, size_t msgsz, int msgflg)
555{
556 struct msg_queue *msq;
557 struct msg_msg *msg;
558 long mtype;
559 int err;
560
561 if (msgsz > msg_ctlmax || (long) msgsz < 0 || msqid < 0)
562 return -EINVAL;
563 if (get_user(mtype, &msgp->mtype))
564 return -EFAULT;
565 if (mtype < 1)
566 return -EINVAL;
567
568 msg = load_msg(msgp->mtext, msgsz);
569 if(IS_ERR(msg))
570 return PTR_ERR(msg);
571
572 msg->m_type = mtype;
573 msg->m_ts = msgsz;
574
575 msq = msg_lock(msqid);
576 err=-EINVAL;
577 if(msq==NULL)
578 goto out_free;
579
580 err= -EIDRM;
581 if (msg_checkid(msq,msqid))
582 goto out_unlock_free;
583
584 for (;;) {
585 struct msg_sender s;
586
587 err=-EACCES;
588 if (ipcperms(&msq->q_perm, S_IWUGO))
589 goto out_unlock_free;
590
591 err = security_msg_queue_msgsnd(msq, msg, msgflg);
592 if (err)
593 goto out_unlock_free;
594
595 if(msgsz + msq->q_cbytes <= msq->q_qbytes &&
596 1 + msq->q_qnum <= msq->q_qbytes) {
597 break;
598 }
599
600 /* queue full, wait: */
601 if(msgflg&IPC_NOWAIT) {
602 err=-EAGAIN;
603 goto out_unlock_free;
604 }
605 ss_add(msq, &s);
606 ipc_rcu_getref(msq);
607 msg_unlock(msq);
608 schedule();
609
610 ipc_lock_by_ptr(&msq->q_perm);
611 ipc_rcu_putref(msq);
612 if (msq->q_perm.deleted) {
613 err = -EIDRM;
614 goto out_unlock_free;
615 }
616 ss_del(&s);
617
618 if (signal_pending(current)) {
619 err=-ERESTARTNOHAND;
620 goto out_unlock_free;
621 }
622 }
623
624 msq->q_lspid = current->tgid;
625 msq->q_stime = get_seconds();
626
627 if(!pipelined_send(msq,msg)) {
628 /* noone is waiting for this message, enqueue it */
629 list_add_tail(&msg->m_list,&msq->q_messages);
630 msq->q_cbytes += msgsz;
631 msq->q_qnum++;
632 atomic_add(msgsz,&msg_bytes);
633 atomic_inc(&msg_hdrs);
634 }
635
636 err = 0;
637 msg = NULL;
638
639out_unlock_free:
640 msg_unlock(msq);
641out_free:
642 if(msg!=NULL)
643 free_msg(msg);
644 return err;
645}
646
647static inline int convert_mode(long* msgtyp, int msgflg)
648{
649 /*
650 * find message of correct type.
651 * msgtyp = 0 => get first.
652 * msgtyp > 0 => get first message of matching type.
653 * msgtyp < 0 => get message with least type must be < abs(msgtype).
654 */
655 if(*msgtyp==0)
656 return SEARCH_ANY;
657 if(*msgtyp<0) {
658 *msgtyp=-(*msgtyp);
659 return SEARCH_LESSEQUAL;
660 }
661 if(msgflg & MSG_EXCEPT)
662 return SEARCH_NOTEQUAL;
663 return SEARCH_EQUAL;
664}
665
666asmlinkage long sys_msgrcv (int msqid, struct msgbuf __user *msgp, size_t msgsz,
667 long msgtyp, int msgflg)
668{
669 struct msg_queue *msq;
670 struct msg_msg *msg;
671 int mode;
672
673 if (msqid < 0 || (long) msgsz < 0)
674 return -EINVAL;
675 mode = convert_mode(&msgtyp,msgflg);
676
677 msq = msg_lock(msqid);
678 if(msq==NULL)
679 return -EINVAL;
680
681 msg = ERR_PTR(-EIDRM);
682 if (msg_checkid(msq,msqid))
683 goto out_unlock;
684
685 for (;;) {
686 struct msg_receiver msr_d;
687 struct list_head* tmp;
688
689 msg = ERR_PTR(-EACCES);
690 if (ipcperms (&msq->q_perm, S_IRUGO))
691 goto out_unlock;
692
693 msg = ERR_PTR(-EAGAIN);
694 tmp = msq->q_messages.next;
695 while (tmp != &msq->q_messages) {
696 struct msg_msg *walk_msg;
697 walk_msg = list_entry(tmp,struct msg_msg,m_list);
698 if(testmsg(walk_msg,msgtyp,mode) &&
699 !security_msg_queue_msgrcv(msq, walk_msg, current, msgtyp, mode)) {
700 msg = walk_msg;
701 if(mode == SEARCH_LESSEQUAL && walk_msg->m_type != 1) {
702 msg=walk_msg;
703 msgtyp=walk_msg->m_type-1;
704 } else {
705 msg=walk_msg;
706 break;
707 }
708 }
709 tmp = tmp->next;
710 }
711 if(!IS_ERR(msg)) {
712 /* Found a suitable message. Unlink it from the queue. */
713 if ((msgsz < msg->m_ts) && !(msgflg & MSG_NOERROR)) {
714 msg = ERR_PTR(-E2BIG);
715 goto out_unlock;
716 }
717 list_del(&msg->m_list);
718 msq->q_qnum--;
719 msq->q_rtime = get_seconds();
720 msq->q_lrpid = current->tgid;
721 msq->q_cbytes -= msg->m_ts;
722 atomic_sub(msg->m_ts,&msg_bytes);
723 atomic_dec(&msg_hdrs);
724 ss_wakeup(&msq->q_senders,0);
725 msg_unlock(msq);
726 break;
727 }
728 /* No message waiting. Wait for a message */
729 if (msgflg & IPC_NOWAIT) {
730 msg = ERR_PTR(-ENOMSG);
731 goto out_unlock;
732 }
733 list_add_tail(&msr_d.r_list,&msq->q_receivers);
734 msr_d.r_tsk = current;
735 msr_d.r_msgtype = msgtyp;
736 msr_d.r_mode = mode;
737 if(msgflg & MSG_NOERROR)
738 msr_d.r_maxsize = INT_MAX;
739 else
740 msr_d.r_maxsize = msgsz;
741 msr_d.r_msg = ERR_PTR(-EAGAIN);
742 current->state = TASK_INTERRUPTIBLE;
743 msg_unlock(msq);
744
745 schedule();
746
747 /* Lockless receive, part 1:
748 * Disable preemption. We don't hold a reference to the queue
749 * and getting a reference would defeat the idea of a lockless
750 * operation, thus the code relies on rcu to guarantee the
751 * existance of msq:
752 * Prior to destruction, expunge_all(-EIRDM) changes r_msg.
753 * Thus if r_msg is -EAGAIN, then the queue not yet destroyed.
754 * rcu_read_lock() prevents preemption between reading r_msg
755 * and the spin_lock() inside ipc_lock_by_ptr().
756 */
757 rcu_read_lock();
758
759 /* Lockless receive, part 2:
760 * Wait until pipelined_send or expunge_all are outside of
761 * wake_up_process(). There is a race with exit(), see
762 * ipc/mqueue.c for the details.
763 */
764 msg = (struct msg_msg*) msr_d.r_msg;
765 while (msg == NULL) {
766 cpu_relax();
767 msg = (struct msg_msg*) msr_d.r_msg;
768 }
769
770 /* Lockless receive, part 3:
771 * If there is a message or an error then accept it without
772 * locking.
773 */
774 if(msg != ERR_PTR(-EAGAIN)) {
775 rcu_read_unlock();
776 break;
777 }
778
779 /* Lockless receive, part 3:
780 * Acquire the queue spinlock.
781 */
782 ipc_lock_by_ptr(&msq->q_perm);
783 rcu_read_unlock();
784
785 /* Lockless receive, part 4:
786 * Repeat test after acquiring the spinlock.
787 */
788 msg = (struct msg_msg*)msr_d.r_msg;
789 if(msg != ERR_PTR(-EAGAIN))
790 goto out_unlock;
791
792 list_del(&msr_d.r_list);
793 if (signal_pending(current)) {
794 msg = ERR_PTR(-ERESTARTNOHAND);
795out_unlock:
796 msg_unlock(msq);
797 break;
798 }
799 }
800 if (IS_ERR(msg))
801 return PTR_ERR(msg);
802
803 msgsz = (msgsz > msg->m_ts) ? msg->m_ts : msgsz;
804 if (put_user (msg->m_type, &msgp->mtype) ||
805 store_msg(msgp->mtext, msg, msgsz)) {
806 msgsz = -EFAULT;
807 }
808 free_msg(msg);
809 return msgsz;
810}
811
812#ifdef CONFIG_PROC_FS
813static int sysvipc_msg_proc_show(struct seq_file *s, void *it)
814{
815 struct msg_queue *msq = it;
816
817 return seq_printf(s,
818 "%10d %10d %4o %10lu %10lu %5u %5u %5u %5u %5u %5u %10lu %10lu %10lu\n",
819 msq->q_perm.key,
820 msq->q_id,
821 msq->q_perm.mode,
822 msq->q_cbytes,
823 msq->q_qnum,
824 msq->q_lspid,
825 msq->q_lrpid,
826 msq->q_perm.uid,
827 msq->q_perm.gid,
828 msq->q_perm.cuid,
829 msq->q_perm.cgid,
830 msq->q_stime,
831 msq->q_rtime,
832 msq->q_ctime);
833}
834#endif