/*
* linux/ipc/sem.c
* Copyright (C) 1992 Krishna Balasubramanian
* Copyright (C) 1995 Eric Schenk, Bruno Haible
*
* IMPLEMENTATION NOTES ON CODE REWRITE (Eric Schenk, January 1995):
* This code underwent a massive rewrite in order to solve some problems
* with the original code. In particular the original code failed to
* wake up processes that were waiting for semval to go to 0 if the
* value went to 0 and was then incremented rapidly enough. In solving
* this problem I have also modified the implementation so that it
* processes pending operations in a FIFO manner, thus give a guarantee
* that processes waiting for a lock on the semaphore won't starve
* unless another locking process fails to unlock.
* In addition the following two changes in behavior have been introduced:
* - The original implementation of semop returned the value
* last semaphore element examined on success. This does not
* match the manual page specifications, and effectively
* allows the user to read the semaphore even if they do not
* have read permissions. The implementation now returns 0
* on success as stated in the manual page.
* - There is some confusion over whether the set of undo adjustments
* to be performed at exit should be done in an atomic manner.
* That is, if we are attempting to decrement the semval should we queue
* up and wait until we can do so legally?
* The original implementation attempted to do this.
* The current implementation does not do so. This is because I don't
* think it is the right thing (TM) to do, and because I couldn't
* see a clean way to get the old behavior with the new design.
* The POSIX standard and SVID should be consulted to determine
* what behavior is mandated.
*/
extern int ipcperms (struct ipc_perm *ipcp, short semflg);
static int newary (key_t, int, int);
static int findkey (key_t key);
static void freeary (int id);
static struct semid_ds *semary[SEMMNI];
static int used_sems = 0, used_semids = 0;
static struct wait_queue *sem_lock = NULL;
static int max_semid = 0;
static unsigned short sem_seq = 0;
void sem_init (void)
{
int i;
sem_lock = NULL;
used_sems = used_semids = max_semid = sem_seq = 0;
for (i = 0; i < SEMMNI; i++)
semary[i] = (struct semid_ds *) IPC_UNUSED;
return;
}
static int findkey (key_t key)
{
int id;
struct semid_ds *sma;
for (id = 0; id <= max_semid; id++) {
while ((sma = semary[id]) == IPC_NOID)
interruptible_sleep_on (&sem_lock);
if (sma == IPC_UNUSED)
continue;
if (key == sma->sem_perm.key)
return id;
}
return -1;
}
static int newary (key_t key, int nsems, int semflg)
{
int id;
struct semid_ds *sma;
struct ipc_perm *ipcp;
int size;
if (!nsems)
return -EINVAL;
if (used_sems + nsems > SEMMNS)
return -ENOSPC;
for (id = 0; id < SEMMNI; id++)
if (semary[id] == IPC_UNUSED) {
semary[id] = (struct semid_ds *) IPC_NOID;
goto found;
}
return -ENOSPC;
found:
size = sizeof (*sma) + nsems * sizeof (struct sem);
used_sems += nsems;
sma = (struct semid_ds *) kmalloc (size, GFP_KERNEL);
if (!sma) {
semary[id] = (struct semid_ds *) IPC_UNUSED;
used_sems -= nsems;
if (sem_lock)
wake_up (&sem_lock);
return -ENOMEM;
}
memset (sma, 0, size);
sma->sem_base = (struct sem *) &sma[1];
ipcp = &sma->sem_perm;
ipcp->mode = (semflg & S_IRWXUGO);
ipcp->key = key;
ipcp->cuid = ipcp->uid = current->euid;
ipcp->gid = ipcp->cgid = current->egid;
sma->sem_perm.seq = sem_seq;
/* sma->sem_pending = NULL; */
sma->sem_pending_last = &sma->sem_pending;
/* sma->undo = NULL; */
sma->sem_nsems = nsems;
sma->sem_ctime = CURRENT_TIME;
if (id > max_semid)
max_semid = id;
used_semids++;
semary[id] = sma;
if (sem_lock)
wake_up (&sem_lock);
return (unsigned int) sma->sem_perm.seq * SEMMNI + id;
}
asmlinkage int sys_semget (key_t key, int nsems, int semflg)
{
int id;
struct semid_ds *sma;
if (nsems < 0 || nsems > SEMMSL)
return -EINVAL;
if (key == IPC_PRIVATE)
return newary(key, nsems, semflg);
if ((id = findkey (key)) == -1) { /* key not used */
if (!(semflg & IPC_CREAT))
return -ENOENT;
return newary(key, nsems, semflg);
}
if (semflg & IPC_CREAT && semflg & IPC_EXCL)
return -EEXIST;
sma = semary[id];
if (nsems > sma->sem_nsems)
return -EINVAL;
if (ipcperms(&sma->sem_perm, semflg))
return -EACCES;
return (unsigned int) sma->sem_perm.seq * SEMMNI + id;
}
/* Manage the doubly linked list sma->sem_pending as a FIFO:
* insert new queue elements at the tail sma->sem_pending_last.
*/
static inline void insert_into_queue (struct semid_ds * sma, struct sem_queue * q)
{
*(q->prev = sma->sem_pending_last) = q;
*(sma->sem_pending_last = &q->next) = NULL;
}
static inline void remove_from_queue (struct semid_ds * sma, struct sem_queue * q)
{
*(q->prev) = q->next;
if (q->next)
q->next->prev = q->prev;
else /* sma->sem_pending_last == &q->next */
sma->sem_pending_last = q->prev;
q->prev = NULL; /* mark as removed */
}
/* Determine whether a sequence of semaphore operations would succeed
* all at once. Return 0 if yes, 1 if need to sleep, else return error code.
*/
static int try_semop (struct semid_ds * sma, struct sembuf * sops, int nsops)
{
int result = 0;
int i = 0;
while (i < nsops) {
struct sembuf * sop = &sops[i];
struct sem * curr = &sma->sem_base[sop->sem_num];
if (sop->sem_op + curr->semval > SEMVMX) {
result = -ERANGE;
break;
}
if (!sop->sem_op && curr->semval) {
if (sop->sem_flg & IPC_NOWAIT)
result = -EAGAIN;
else
result = 1;
break;
}
i++;
curr->semval += sop->sem_op;
if (curr->semval < 0) {
if (sop->sem_flg & IPC_NOWAIT)
result = -EAGAIN;
else
result = 1;
break;
}
}
while (--i >= 0) {
struct sembuf * sop = &sops[i];
struct sem * curr = &sma->sem_base[sop->sem_num];
curr->semval -= sop->sem_op;
}
return result;
}
/* Actually perform a sequence of semaphore operations. Atomically. */
/* This assumes that try_semop() already returned 0. */
static int do_semop (struct semid_ds * sma, struct sembuf * sops, int nsops,
struct sem_undo * un, int pid)
{
int i;
for (i = 0; i < nsops; i++) {
struct sembuf * sop = &sops[i];
struct sem * curr = &sma->sem_base[sop->sem_num];
if (sop->sem_op + curr->semval > SEMVMX) {
printk("do_semop: race\n");
break;
}
if (!sop->sem_op) {
if (curr->semval) {
printk("do_semop: race\n");
break;
}
} else {
curr->semval += sop->sem_op;
if (curr->semval < 0) {
printk("do_semop: race\n");
break;
}
if (sop->sem_flg & SEM_UNDO)
un->semadj[sop->sem_num] -= sop->sem_op;
}
curr->sempid = pid;
}
sma->sem_otime = CURRENT_TIME;
/* Previous implementation returned the last semaphore's semval.
* This is wrong because we may not have checked read permission,
* only write permission.
*/
return 0;
}
/* Go through the pending queue for the indicated semaphore
* looking for tasks that can be completed. Keep cycling through
* the queue until a pass is made in which no process is woken up.
*/
static void update_queue (struct semid_ds * sma)
{
int wokeup, error;
struct sem_queue * q;
do {
wokeup = 0;
for (q = sma->sem_pending; q; q = q->next) {
error = try_semop(sma, q->sops, q->nsops);
/* Does q->sleeper still need to sleep? */
if (error > 0)
continue;
/* Perform the operations the sleeper was waiting for */
if (!error)
error = do_semop(sma, q->sops, q->nsops, q->undo, q->pid);
q->status = error;
/* Remove it from the queue */
remove_from_queue(sma,q);
/* Wake it up */
wake_up_interruptible(&q->sleeper); /* doesn't sleep! */
wokeup++;
}
} while (wokeup);
}
/* The following counts are associated to each semaphore:
* semncnt number of tasks waiting on semval being nonzero
* semzcnt number of tasks waiting on semval being zero
* This model assumes that a task waits on exactly one semaphore.
* Since semaphore operations are to be performed atomically, tasks actually
* wait on a whole sequence of semaphores simultaneously.
* The counts we return here are a rough approximation, but still
* warrant that semncnt+semzcnt>0 if the task is on the pending queue.
*/
static int count_semncnt (struct semid_ds * sma, ushort semnum)
{
int semncnt;
struct sem_queue * q;
semncnt = 0;
for (q = sma->sem_pending; q; q = q->next) {
struct sembuf * sops = q->sops;
int nsops = q->nsops;
int i;
for (i = 0; i < nsops; i++)
if (sops[i].sem_num == semnum
&& (sops[i].sem_op < 0)
&& !(sops[i].sem_flg & IPC_NOWAIT))
semncnt++;
}
return semncnt;
}
static int count_semzcnt (struct semid_ds * sma, ushort semnum)
{
int semzcnt;
struct sem_queue * q;
semzcnt = 0;
for (q = sma->sem_pending; q; q = q->next) {
struct sembuf * sops = q->sops;
int nsops = q->nsops;
int i;
for (i = 0; i < nsops; i++)
if (sops[i].sem_num == semnum
&& (sops[i].sem_op == 0)
&& !(sops[i].sem_flg & IPC_NOWAIT))
semzcnt++;
}
return semzcnt;
}
/* Free a semaphore set. */
static void freeary (int id)
{
struct semid_ds *sma = semary[id];
struct sem_undo *un;
struct sem_queue *q;
/* Invalidate this semaphore set */
sma->sem_perm.seq++;
sem_seq = (sem_seq+1) % ((unsigned)(1<<31)/SEMMNI); /* increment, but avoid overflow */
used_sems -= sma->sem_nsems;
if (id == max_semid)
while (max_semid && (semary[--max_semid] == IPC_UNUSED));
semary[id] = (struct semid_ds *) IPC_UNUSED;
used_semids--;
/* Invalidate the existing undo structures for this semaphore set.
* (They will be freed without any further action in sem_exit().)
*/
for (un = sma->undo; un; un = un->id_next)
un->semid = -1;
/* Wake up all pending processes and let them fail with EIDRM. */
for (q = sma->sem_pending; q; q = q->next) {
q->status = -EIDRM;
q->prev = NULL;
wake_up_interruptible(&q->sleeper); /* doesn't sleep! */
}
kfree(sma);
}
asmlinkage int sys_semctl (int semid, int semnum, int cmd, union semun arg)
{
struct semid_ds *buf = NULL;
struct semid_ds tbuf;
int i, id, val = 0;
struct semid_ds *sma;
struct ipc_perm *ipcp;
struct sem *curr = NULL;
struct sem_undo *un;
unsigned int nsems;
ushort *array = NULL;
ushort sem_io[SEMMSL];
if (semid < 0 || semnum < 0 || cmd < 0)
return -EINVAL;
switch (cmd) {
case IPC_INFO:
case SEM_INFO:
{
struct seminfo seminfo, *tmp = arg.__buf;
seminfo.semmni = SEMMNI;
seminfo.semmns = SEMMNS;
seminfo.semmsl = SEMMSL;
seminfo.semopm = SEMOPM;
seminfo.semvmx = SEMVMX;
seminfo.semmnu = SEMMNU;
seminfo.semmap = SEMMAP;
seminfo.semume = SEMUME;
seminfo.semusz = SEMUSZ;
seminfo.semaem = SEMAEM;
if (cmd == SEM_INFO) {
seminfo.semusz = used_semids;
seminfo.semaem = used_sems;
}
i = verify_area(VERIFY_WRITE, tmp, sizeof(struct seminfo));
if (i)
return i;
memcpy_tofs (tmp, &seminfo, sizeof(struct seminfo));
return max_semid;
}
case SEM_STAT:
buf = arg.buf;
i = verify_area (VERIFY_WRITE, buf, sizeof (*buf));
if (i)
return i;
if (semid > max_semid)
return -EINVAL;
sma = semary[semid];
if (sma == IPC_UNUSED || sma == IPC_NOID)
return -EINVAL;
if (ipcperms (&sma->sem_perm, S_IRUGO))
return -EACCES;
id = (unsigned int) sma->sem_perm.seq * SEMMNI + semid;
tbuf.sem_perm = sma->sem_perm;
tbuf.sem_otime = sma->sem_otime;
tbuf.sem_ctime = sma->sem_ctime;
tbuf.sem_nsems = sma->sem_nsems;
memcpy_tofs (buf, &tbuf, sizeof(*buf));
return id;
}
id = (unsigned int) semid % SEMMNI;
sma = semary [id];
if (sma == IPC_UNUSED || sma == IPC_NOID)
return -EINVAL;
ipcp = &sma->sem_perm;
nsems = sma->sem_nsems;
if (sma->sem_perm.seq != (unsigned int) semid / SEMMNI)
return -EIDRM;
switch (cmd) {
case GETVAL:
case GETPID:
case GETNCNT:
case GETZCNT:
case SETVAL:
if (semnum >= nsems)
return -EINVAL;
curr = &sma->sem_base[semnum];
break;
}
switch (cmd) {
case GETVAL:
case GETPID:
case GETNCNT:
case GETZCNT:
case GETALL:
if (ipcperms (ipcp, S_IRUGO))
return -EACCES;
switch (cmd) {
case GETVAL : return curr->semval;
case GETPID : return curr->sempid;
case GETNCNT: return count_semncnt(sma,semnum);
case GETZCNT: return count_semzcnt(sma,semnum);
case GETALL:
array = arg.array;
i = verify_area (VERIFY_WRITE, array, nsems*sizeof(ushort));
if (i)
return i;
}
break;
case SETVAL:
val = arg.val;
if (val > SEMVMX || val < 0)
return -ERANGE;
break;
case IPC_RMID:
if (suser() || current->euid == ipcp->cuid || current->euid == ipcp->uid) {
freeary (id);
return 0;
}
return -EPERM;
case SETALL: /* arg is a pointer to an array of ushort */
array = arg.array;
if ((i = verify_area (VERIFY_READ, array, nsems*sizeof(ushort))))
return i;
memcpy_fromfs (sem_io, array, nsems*sizeof(ushort));
for (i = 0; i < nsems; i++)
if (sem_io[i] > SEMVMX)
return -ERANGE;
break;
case IPC_STAT:
buf = arg.buf;
if ((i = verify_area (VERIFY_WRITE, buf, sizeof(*buf))))
return i;
break;
case IPC_SET:
buf = arg.buf;
if ((i = verify_area (VERIFY_READ, buf, sizeof (*buf))))
return i;
memcpy_fromfs (&tbuf, buf, sizeof (*buf));
break;
}
if (semary[id] == IPC_UNUSED || semary[id] == IPC_NOID)
return -EIDRM;
if (sma->sem_perm.seq != (unsigned int) semid / SEMMNI)
return -EIDRM;
switch (cmd) {
case GETALL:
if (ipcperms (ipcp, S_IRUGO))
return -EACCES;
for (i = 0; i < sma->sem_nsems; i++)
sem_io[i] = sma->sem_base[i].semval;
memcpy_tofs (array, sem_io, nsems*sizeof(ushort));
break;
case SETVAL:
if (ipcperms (ipcp, S_IWUGO))
return -EACCES;
for (un = sma->undo; un; un = un->id_next)
un->semadj[semnum] = 0;
curr->semval = val;
sma->sem_ctime = CURRENT_TIME;
/* maybe some queued-up processes were waiting for this */
update_queue(sma);
break;
case IPC_SET:
if (suser() || current->euid == ipcp->cuid || current->euid == ipcp->uid) {
ipcp->uid = tbuf.sem_perm.uid;
ipcp->gid = tbuf.sem_perm.gid;
ipcp->mode = (ipcp->mode & ~S_IRWXUGO)
| (tbuf.sem_perm.mode & S_IRWXUGO);
sma->sem_ctime = CURRENT_TIME;
return 0;
}
return -EPERM;
case IPC_STAT:
if (ipcperms (ipcp, S_IRUGO))
return -EACCES;
tbuf.sem_perm = sma->sem_perm;
tbuf.sem_otime = sma->sem_otime;
tbuf.sem_ctime = sma->sem_ctime;
tbuf.sem_nsems = sma->sem_nsems;
memcpy_tofs (buf, &tbuf, sizeof(*buf));
break;
case SETALL:
if (ipcperms (ipcp, S_IWUGO))
return -EACCES;
for (i = 0; i < nsems; i++)
sma->sem_base[i].semval = sem_io[i];
for (un = sma->undo; un; un = un->id_next)
for (i = 0; i < nsems; i++)
un->semadj[i] = 0;
sma->sem_ctime = CURRENT_TIME;
/* maybe some queued-up processes were waiting for this */
update_queue(sma);
break;
default:
return -EINVAL;
}
return 0;
}
asmlinkage int sys_semop (int semid, struct sembuf *tsops, unsigned nsops)
{
int i, id, size, error;
struct semid_ds *sma;
struct sembuf sops[SEMOPM], *sop;
struct sem_undo *un;
int undos = 0, alter = 0;
if (nsops < 1 || semid < 0)
return -EINVAL;
if (nsops > SEMOPM)
return -E2BIG;
if (!tsops)
return -EFAULT;
if ((i = verify_area (VERIFY_READ, tsops, nsops * sizeof(*tsops))))
return i;
memcpy_fromfs (sops, tsops, nsops * sizeof(*tsops));
id = (unsigned int) semid % SEMMNI;
if ((sma = semary[id]) == IPC_UNUSED || sma == IPC_NOID)
return -EINVAL;
if (sma->sem_perm.seq != (unsigned int) semid / SEMMNI)
return -EIDRM;
for (i = 0; i < nsops; i++) {
sop = &sops[i];
if (sop->sem_num >= sma->sem_nsems)
return -EFBIG;
if (sop->sem_flg & SEM_UNDO)
undos++;
if (sop->sem_op)
alter++;
}
if (ipcperms(&sma->sem_perm, alter ? S_IWUGO : S_IRUGO))
return -EACCES;
error = try_semop(sma, sops, nsops);
if (error < 0)
return error;
if (undos) {
/* Make sure we have an undo structure
* for this process and this semaphore set.
*/
for (un = current->semundo; un; un = un->proc_next)
if (un->semid == semid)
break;
if (!un) {
size = sizeof(struct sem_undo) + sizeof(short)*sma->sem_nsems;
un = (struct sem_undo *) kmalloc(size, GFP_ATOMIC);
if (!un)
return -ENOMEM;
memset(un, 0, size);
un->semadj = (short *) &un[1];
un->semid = semid;
un->proc_next = current->semundo;
current->semundo = un;
un->id_next = sma->undo;
sma->undo = un;
}
} else
un = NULL;
if (error == 0) {
/* the operations go through immediately */
error = do_semop(sma, sops, nsops, un, current->pid);
/* maybe some queued-up processes were waiting for this */
update_queue(sma);
return error;
} else {
/* We need to sleep on this operation, so we put the current
* task into the pending queue and go to sleep.
*/
struct sem_queue queue;
queue.sma = sma;
queue.sops = sops;
queue.nsops = nsops;
queue.undo = un;
queue.pid = current->pid;
queue.status = 0;
insert_into_queue(sma,&queue);
queue.sleeper = NULL;
current->semsleeping = &queue;
interruptible_sleep_on(&queue.sleeper);
current->semsleeping = NULL;
/* When we wake up, either the operation is finished,
* or some kind of error happened.
*/
if (!queue.prev) {
/* operation is finished, update_queue() removed us */
return queue.status;
} else {
remove_from_queue(sma,&queue);
return -EINTR;
}
}
}
/*
* add semadj values to semaphores, free undo structures.
* undo structures are not freed when semaphore arrays are destroyed
* so some of them may be out of date.
* IMPLEMENTATION NOTE: There is some confusion over whether the
* set of adjustments that needs to be done should be done in an atomic
* manner or not. That is, if we are attempting to decrement the semval
* should we queue up and wait until we can do so legally?
* The original implementation attempted to do this (queue and wait).
* The current implementation does not do so. The POSIX standard
* and SVID should be consulted to determine what behavior is mandated.
*/
void sem_exit (void)
{
struct sem_queue *q;
struct sem_undo *u, *un = NULL, **up, **unp;
struct semid_ds *sma;
int nsems, i;
/* If the current process was sleeping for a semaphore,
* remove it from the queue.
*/
if ((q = current->semsleeping)) {
if (q->prev)
remove_from_queue(q->sma,q);
current->semsleeping = NULL;
}
for (up = ¤t->semundo; (u = *up); *up = u->proc_next, kfree(u)) {
if (u->semid == -1)
continue;
sma = semary[(unsigned int) u->semid % SEMMNI];
if (sma == IPC_UNUSED || sma == IPC_NOID)
continue;
if (sma->sem_perm.seq != (unsigned int) u->semid / SEMMNI)
continue;
/* remove u from the sma->undo list */
for (unp = &sma->undo; (un = *unp); unp = &un->id_next) {
if (u == un)
goto found;
}
printk ("sem_exit undo list error id=%d\n", u->semid);
break;
found:
*unp = un->id_next;
/* perform adjustments registered in u */
nsems = sma->sem_nsems;
for (i = 0; i < nsems; i++) {
struct sem * sem = &sma->sem_base[i];
sem->semval += u->semadj[i];
if (sem->semval < 0)
sem->semval = 0; /* shouldn't happen */
sem->sempid = current->pid;
}
sma->sem_otime = CURRENT_TIME;
/* maybe some queued-up processes were waiting for this */
update_queue(sma);
}
current->semundo = NULL;
}