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/*
* 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.
*
* Further notes on refinement (Christoph Rohland, December 1998):
* - The POSIX standard says, that the undo adjustments simply should
* redo. So the current implementation is o.K.
* - The previous code had two flaws:
* 1) It actively gave the semaphore to the next waiting process
* sleeping on the semaphore. Since this process did not have the
* cpu this led to many unnecessary context switches and bad
* performance. Now we only check which process should be able to
* get the semaphore and if this process wants to reduce some
* semaphore value we simply wake it up without doing the
* operation. So it has to try to get it later. Thus e.g. the
* running process may reacquire the semaphore during the current
* time slice. If it only waits for zero or increases the semaphore,
* we do the operation in advance and wake it up.
* 2) It did not wake up all zero waiting processes. We try to do
* better but only get the semops right which only wait for zero or
* increase. If there are decrement operations in the operations
* array we do the same as before.
*
* /proc/sysvipc/sem support (c) 1999 Dragos Acostachioaie <dragos@iname.com>
*
* SMP-threaded, sysctl's added
* (c) 1999 Manfred Spraul <manfreds@colorfullife.com>
* Enforced range limit on SEM_UNDO
* (c) 2001 Red Hat Inc <alan@redhat.com>
*/
#include <linux/config.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/init.h>
#include <linux/proc_fs.h>
#include <asm/uaccess.h>
#include "util.h"
#define sem_lock(id) ((struct sem_array*)ipc_lock(&sem_ids,id))
#define sem_unlock(id) ipc_unlock(&sem_ids,id)
#define sem_rmid(id) ((struct sem_array*)ipc_rmid(&sem_ids,id))
#define sem_checkid(sma, semid) \
ipc_checkid(&sem_ids,&sma->sem_perm,semid)
#define sem_buildid(id, seq) \
ipc_buildid(&sem_ids, id, seq)
static struct ipc_ids sem_ids;
static int newary (key_t, int, int);
static void freeary (int id);
#ifdef CONFIG_PROC_FS
static int sysvipc_sem_read_proc(char *buffer, char **start, off_t offset, int length, int *eof, void *data);
#endif
#define SEMMSL_FAST 256 /* 512 bytes on stack */
#define SEMOPM_FAST 64 /* ~ 372 bytes on stack */
/*
* linked list protection:
* sem_undo.id_next,
* sem_array.sem_pending{,last},
* sem_array.sem_undo: sem_lock() for read/write
* sem_undo.proc_next: only "current" is allowed to read/write that field.
*
*/
int sem_ctls[4] = {SEMMSL, SEMMNS, SEMOPM, SEMMNI};
#define sc_semmsl (sem_ctls[0])
#define sc_semmns (sem_ctls[1])
#define sc_semopm (sem_ctls[2])
#define sc_semmni (sem_ctls[3])
static int used_sems;
void __init sem_init (void)
{
used_sems = 0;
ipc_init_ids(&sem_ids,sc_semmni);
#ifdef CONFIG_PROC_FS
create_proc_read_entry("sysvipc/sem", 0, 0, sysvipc_sem_read_proc, NULL);
#endif
}
static int newary (key_t key, int nsems, int semflg)
{
int id;
struct sem_array *sma;
int size;
if (!nsems)
return -EINVAL;
if (used_sems + nsems > sc_semmns)
return -ENOSPC;
size = sizeof (*sma) + nsems * sizeof (struct sem);
sma = (struct sem_array *) ipc_alloc(size);
if (!sma) {
return -ENOMEM;
}
memset (sma, 0, size);
id = ipc_addid(&sem_ids, &sma->sem_perm, sc_semmni);
if(id == -1) {
ipc_free(sma, size);
return -ENOSPC;
}
used_sems += nsems;
sma->sem_perm.mode = (semflg & S_IRWXUGO);
sma->sem_perm.key = key;
sma->sem_base = (struct sem *) &sma[1];
/* sma->sem_pending = NULL; */
sma->sem_pending_last = &sma->sem_pending;
/* sma->undo = NULL; */
sma->sem_nsems = nsems;
sma->sem_ctime = CURRENT_TIME;
sem_unlock(id);
return sem_buildid(id, sma->sem_perm.seq);
}
asmlinkage long sys_semget (key_t key, int nsems, int semflg)
{
int id, err = -EINVAL;
struct sem_array *sma;
if (nsems < 0 || nsems > sc_semmsl)
return -EINVAL;
down(&sem_ids.sem);
if (key == IPC_PRIVATE) {
err = newary(key, nsems, semflg);
} else if ((id = ipc_findkey(&sem_ids, key)) == -1) { /* key not used */
if (!(semflg & IPC_CREAT))
err = -ENOENT;
else
err = newary(key, nsems, semflg);
} else if (semflg & IPC_CREAT && semflg & IPC_EXCL) {
err = -EEXIST;
} else {
sma = sem_lock(id);
if(sma==NULL)
BUG();
if (nsems > sma->sem_nsems)
err = -EINVAL;
else if (ipcperms(&sma->sem_perm, semflg))
err = -EACCES;
else
err = sem_buildid(id, sma->sem_perm.seq);
sem_unlock(id);
}
up(&sem_ids.sem);
return err;
}
/* doesn't acquire the sem_lock on error! */
static int sem_revalidate(int semid, struct sem_array* sma, int nsems, short flg)
{
struct sem_array* smanew;
smanew = sem_lock(semid);
if(smanew==NULL)
return -EIDRM;
if(smanew != sma || sem_checkid(sma,semid) || sma->sem_nsems != nsems) {
sem_unlock(semid);
return -EIDRM;
}
if (ipcperms(&sma->sem_perm, flg)) {
sem_unlock(semid);
return -EACCES;
}
return 0;
}
/* 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 append_to_queue (struct sem_array * sma,
struct sem_queue * q)
{
*(q->prev = sma->sem_pending_last) = q;
*(sma->sem_pending_last = &q->next) = NULL;
}
static inline void prepend_to_queue (struct sem_array * sma,
struct sem_queue * q)
{
q->next = sma->sem_pending;
*(q->prev = &sma->sem_pending) = q;
if (q->next)
q->next->prev = &q->next;
else /* sma->sem_pending_last == &sma->sem_pending */
sma->sem_pending_last = &q->next;
}
static inline void remove_from_queue (struct sem_array * 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_atomic_semop (struct sem_array * sma, struct sembuf * sops,
int nsops, struct sem_undo *un, int pid,
int do_undo)
{
int result, sem_op;
struct sembuf *sop;
struct sem * curr;
for (sop = sops; sop < sops + nsops; sop++) {
curr = sma->sem_base + sop->sem_num;
sem_op = sop->sem_op;
if (!sem_op && curr->semval)
goto would_block;
curr->sempid = (curr->sempid << 16) | pid;
curr->semval += sem_op;
if (sop->sem_flg & SEM_UNDO)
{
int undo = un->semadj[sop->sem_num] - sem_op;
/*
* Exceeding the undo range is an error.
*/
if (undo < (-SEMAEM - 1) || undo > SEMAEM)
{
/* Don't undo the undo */
sop->sem_flg &= ~SEM_UNDO;
goto out_of_range;
}
un->semadj[sop->sem_num] = undo;
}
if (curr->semval < 0)
goto would_block;
if (curr->semval > SEMVMX)
goto out_of_range;
}
if (do_undo)
{
sop--;
result = 0;
goto undo;
}
sma->sem_otime = CURRENT_TIME;
return 0;
out_of_range:
result = -ERANGE;
goto undo;
would_block:
if (sop->sem_flg & IPC_NOWAIT)
result = -EAGAIN;
else
result = 1;
undo:
while (sop >= sops) {
curr = sma->sem_base + sop->sem_num;
curr->semval -= sop->sem_op;
curr->sempid >>= 16;
if (sop->sem_flg & SEM_UNDO)
un->semadj[sop->sem_num] += sop->sem_op;
sop--;
}
return result;
}
/* Go through the pending queue for the indicated semaphore
* looking for tasks that can be completed.
*/
static void update_queue (struct sem_array * sma)
{
int error;
struct sem_queue * q;
for (q = sma->sem_pending; q; q = q->next) {
if (q->status == 1)
continue; /* this one was woken up before */
error = try_atomic_semop(sma, q->sops, q->nsops,
q->undo, q->pid, q->alter);
/* Does q->sleeper still need to sleep? */
if (error <= 0) {
/* Found one, wake it up */
wake_up_process(q->sleeper);
if (error == 0 && q->alter) {
/* if q-> alter let it self try */
q->status = 1;
return;
}
q->status = error;
remove_from_queue(sma,q);
}
}
}
/* 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 sem_array * 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 sem_array * 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 sem_array *sma;
struct sem_undo *un;
struct sem_queue *q;
int size;
sma = sem_rmid(id);
/* Invalidate the existing undo structures for this semaphore set.
* (They will be freed without any further action in sem_exit()
* or during the next semop.)
*/
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_process(q->sleeper); /* doesn't sleep */
}
sem_unlock(id);
used_sems -= sma->sem_nsems;
size = sizeof (*sma) + sma->sem_nsems * sizeof (struct sem);
ipc_free(sma, size);
}
static unsigned long copy_semid_to_user(void *buf, struct semid64_ds *in, int version)
{
switch(version) {
case IPC_64:
return copy_to_user(buf, in, sizeof(*in));
case IPC_OLD:
{
struct semid_ds out;
ipc64_perm_to_ipc_perm(&in->sem_perm, &out.sem_perm);
out.sem_otime = in->sem_otime;
out.sem_ctime = in->sem_ctime;
out.sem_nsems = in->sem_nsems;
return copy_to_user(buf, &out, sizeof(out));
}
default:
return -EINVAL;
}
}
int semctl_nolock(int semid, int semnum, int cmd, int version, union semun arg)
{
int err = -EINVAL;
switch(cmd) {
case IPC_INFO:
case SEM_INFO:
{
struct seminfo seminfo;
int max_id;
memset(&seminfo,0,sizeof(seminfo));
seminfo.semmni = sc_semmni;
seminfo.semmns = sc_semmns;
seminfo.semmsl = sc_semmsl;
seminfo.semopm = sc_semopm;
seminfo.semvmx = SEMVMX;
seminfo.semmnu = SEMMNU;
seminfo.semmap = SEMMAP;
seminfo.semume = SEMUME;
down(&sem_ids.sem);
if (cmd == SEM_INFO) {
seminfo.semusz = sem_ids.in_use;
seminfo.semaem = used_sems;
} else {
seminfo.semusz = SEMUSZ;
seminfo.semaem = SEMAEM;
}
max_id = sem_ids.max_id;
up(&sem_ids.sem);
if (copy_to_user (arg.__buf, &seminfo, sizeof(struct seminfo)))
return -EFAULT;
return (max_id < 0) ? 0: max_id;
}
case SEM_STAT:
{
struct sem_array *sma;
struct semid64_ds tbuf;
int id;
if(semid >= sem_ids.size)
return -EINVAL;
memset(&tbuf,0,sizeof(tbuf));
sma = sem_lock(semid);
if(sma == NULL)
return -EINVAL;
err = -EACCES;
if (ipcperms (&sma->sem_perm, S_IRUGO))
goto out_unlock;
id = sem_buildid(semid, sma->sem_perm.seq);
kernel_to_ipc64_perm(&sma->sem_perm, &tbuf.sem_perm);
tbuf.sem_otime = sma->sem_otime;
tbuf.sem_ctime = sma->sem_ctime;
tbuf.sem_nsems = sma->sem_nsems;
sem_unlock(semid);
if (copy_semid_to_user (arg.buf, &tbuf, version))
return -EFAULT;
return id;
}
default:
return -EINVAL;
}
return err;
out_unlock:
sem_unlock(semid);
return err;
}
int semctl_main(int semid, int semnum, int cmd, int version, union semun arg)
{
struct sem_array *sma;
struct sem* curr;
int err;
ushort fast_sem_io[SEMMSL_FAST];
ushort* sem_io = fast_sem_io;
int nsems;
sma = sem_lock(semid);
if(sma==NULL)
return -EINVAL;
nsems = sma->sem_nsems;
err=-EIDRM;
if (sem_checkid(sma,semid))
goto out_unlock;
err = -EACCES;
if (ipcperms (&sma->sem_perm, (cmd==SETVAL||cmd==SETALL)?S_IWUGO:S_IRUGO))
goto out_unlock;
switch (cmd) {
case GETALL:
{
ushort *array = arg.array;
int i;
if(nsems > SEMMSL_FAST) {
sem_unlock(semid);
sem_io = ipc_alloc(sizeof(ushort)*nsems);
if(sem_io == NULL)
return -ENOMEM;
err = sem_revalidate(semid, sma, nsems, S_IRUGO);
if(err)
goto out_free;
}
for (i = 0; i < sma->sem_nsems; i++)
sem_io[i] = sma->sem_base[i].semval;
sem_unlock(semid);
err = 0;
if(copy_to_user(array, sem_io, nsems*sizeof(ushort)))
err = -EFAULT;
goto out_free;
}
case SETALL:
{
int i;
struct sem_undo *un;
sem_unlock(semid);
if(nsems > SEMMSL_FAST) {
sem_io = ipc_alloc(sizeof(ushort)*nsems);
if(sem_io == NULL)
return -ENOMEM;
}
if (copy_from_user (sem_io, arg.array, nsems*sizeof(ushort))) {
err = -EFAULT;
goto out_free;
}
for (i = 0; i < nsems; i++) {
if (sem_io[i] > SEMVMX) {
err = -ERANGE;
goto out_free;
}
}
err = sem_revalidate(semid, sma, nsems, S_IWUGO);
if(err)
goto out_free;
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);
err = 0;
goto out_unlock;
}
case IPC_STAT:
{
struct semid64_ds tbuf;
memset(&tbuf,0,sizeof(tbuf));
kernel_to_ipc64_perm(&sma->sem_perm, &tbuf.sem_perm);
tbuf.sem_otime = sma->sem_otime;
tbuf.sem_ctime = sma->sem_ctime;
tbuf.sem_nsems = sma->sem_nsems;
sem_unlock(semid);
if (copy_semid_to_user (arg.buf, &tbuf, version))
return -EFAULT;
return 0;
}
/* GETVAL, GETPID, GETNCTN, GETZCNT, SETVAL: fall-through */
}
err = -EINVAL;
if(semnum < 0 || semnum >= nsems)
goto out_unlock;
curr = &sma->sem_base[semnum];
switch (cmd) {
case GETVAL:
err = curr->semval;
goto out_unlock;
case GETPID:
err = curr->sempid & 0xffff;
goto out_unlock;
case GETNCNT:
err = count_semncnt(sma,semnum);
goto out_unlock;
case GETZCNT:
err = count_semzcnt(sma,semnum);
goto out_unlock;
case SETVAL:
{
int val = arg.val;
struct sem_undo *un;
err = -ERANGE;
if (val > SEMVMX || val < 0)
goto out_unlock;
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);
err = 0;
goto out_unlock;
}
}
out_unlock:
sem_unlock(semid);
out_free:
if(sem_io != fast_sem_io)
ipc_free(sem_io, sizeof(ushort)*nsems);
return err;
}
struct sem_setbuf {
uid_t uid;
gid_t gid;
mode_t mode;
};
static inline unsigned long copy_semid_from_user(struct sem_setbuf *out, void *buf, int version)
{
switch(version) {
case IPC_64:
{
struct semid64_ds tbuf;
if(copy_from_user(&tbuf, buf, sizeof(tbuf)))
return -EFAULT;
out->uid = tbuf.sem_perm.uid;
out->gid = tbuf.sem_perm.gid;
out->mode = tbuf.sem_perm.mode;
return 0;
}
case IPC_OLD:
{
struct semid_ds tbuf_old;
if(copy_from_user(&tbuf_old, buf, sizeof(tbuf_old)))
return -EFAULT;
out->uid = tbuf_old.sem_perm.uid;
out->gid = tbuf_old.sem_perm.gid;
out->mode = tbuf_old.sem_perm.mode;
return 0;
}
default:
return -EINVAL;
}
}
int semctl_down(int semid, int semnum, int cmd, int version, union semun arg)
{
struct sem_array *sma;
int err;
struct sem_setbuf setbuf;
struct kern_ipc_perm *ipcp;
if(cmd == IPC_SET) {
if(copy_semid_from_user (&setbuf, arg.buf, version))
return -EFAULT;
}
sma = sem_lock(semid);
if(sma==NULL)
return -EINVAL;
if (sem_checkid(sma,semid)) {
err=-EIDRM;
goto out_unlock;
}
ipcp = &sma->sem_perm;
if (current->euid != ipcp->cuid &&
current->euid != ipcp->uid && !capable(CAP_SYS_ADMIN)) {
err=-EPERM;
goto out_unlock;
}
switch(cmd){
case IPC_RMID:
freeary(semid);
err = 0;
break;
case IPC_SET:
ipcp->uid = setbuf.uid;
ipcp->gid = setbuf.gid;
ipcp->mode = (ipcp->mode & ~S_IRWXUGO)
| (setbuf.mode & S_IRWXUGO);
sma->sem_ctime = CURRENT_TIME;
sem_unlock(semid);
err = 0;
break;
default:
sem_unlock(semid);
err = -EINVAL;
break;
}
return err;
out_unlock:
sem_unlock(semid);
return err;
}
asmlinkage long sys_semctl (int semid, int semnum, int cmd, union semun arg)
{
int err = -EINVAL;
int version;
if (semid < 0)
return -EINVAL;
version = ipc_parse_version(&cmd);
switch(cmd) {
case IPC_INFO:
case SEM_INFO:
case SEM_STAT:
err = semctl_nolock(semid,semnum,cmd,version,arg);
return err;
case GETALL:
case GETVAL:
case GETPID:
case GETNCNT:
case GETZCNT:
case IPC_STAT:
case SETVAL:
case SETALL:
err = semctl_main(semid,semnum,cmd,version,arg);
return err;
case IPC_RMID:
case IPC_SET:
down(&sem_ids.sem);
err = semctl_down(semid,semnum,cmd,version,arg);
up(&sem_ids.sem);
return err;
default:
return -EINVAL;
}
}
static struct sem_undo* freeundos(struct sem_array *sma, struct sem_undo* un)
{
struct sem_undo* u;
struct sem_undo** up;
for(up = ¤t->semundo;(u=*up);up=&u->proc_next) {
if(un==u) {
un=u->proc_next;
*up=un;
kfree(u);
return un;
}
}
printk ("freeundos undo list error id=%d\n", un->semid);
return un->proc_next;
}
/* returns without sem_lock on error! */
static int alloc_undo(struct sem_array *sma, struct sem_undo** unp, int semid, int alter)
{
int size, nsems, error;
struct sem_undo *un;
nsems = sma->sem_nsems;
size = sizeof(struct sem_undo) + sizeof(short)*nsems;
sem_unlock(semid);
un = (struct sem_undo *) kmalloc(size, GFP_KERNEL);
if (!un)
return -ENOMEM;
memset(un, 0, size);
error = sem_revalidate(semid, sma, nsems, alter ? S_IWUGO : S_IRUGO);
if(error) {
kfree(un);
return error;
}
un->semadj = (short *) &un[1];
un->semid = semid;
un->proc_next = current->semundo;
current->semundo = un;
un->id_next = sma->undo;
sma->undo = un;
*unp = un;
return 0;
}
asmlinkage long sys_semop (int semid, struct sembuf *tsops, unsigned nsops)
{
int error = -EINVAL;
struct sem_array *sma;
struct sembuf fast_sops[SEMOPM_FAST];
struct sembuf* sops = fast_sops, *sop;
struct sem_undo *un;
int undos = 0, decrease = 0, alter = 0;
struct sem_queue queue;
if (nsops < 1 || semid < 0)
return -EINVAL;
if (nsops > sc_semopm)
return -E2BIG;
if(nsops > SEMOPM_FAST) {
sops = kmalloc(sizeof(*sops)*nsops,GFP_KERNEL);
if(sops==NULL)
return -ENOMEM;
}
if (copy_from_user (sops, tsops, nsops * sizeof(*tsops))) {
error=-EFAULT;
goto out_free;
}
sma = sem_lock(semid);
error=-EINVAL;
if(sma==NULL)
goto out_free;
error = -EIDRM;
if (sem_checkid(sma,semid))
goto out_unlock_free;
error = -EFBIG;
for (sop = sops; sop < sops + nsops; sop++) {
if (sop->sem_num >= sma->sem_nsems)
goto out_unlock_free;
if (sop->sem_flg & SEM_UNDO)
undos++;
if (sop->sem_op < 0)
decrease = 1;
if (sop->sem_op > 0)
alter = 1;
}
alter |= decrease;
error = -EACCES;
if (ipcperms(&sma->sem_perm, alter ? S_IWUGO : S_IRUGO))
goto out_unlock_free;
if (undos) {
/* Make sure we have an undo structure
* for this process and this semaphore set.
*/
un=current->semundo;
while(un != NULL) {
if(un->semid==semid)
break;
if(un->semid==-1)
un=freeundos(sma,un);
else
un=un->proc_next;
}
if (!un) {
error = alloc_undo(sma,&un,semid,alter);
if(error)
goto out_free;
}
} else
un = NULL;
error = try_atomic_semop (sma, sops, nsops, un, current->pid, 0);
if (error <= 0)
goto update;
/* We need to sleep on this operation, so we put the current
* task into the pending queue and go to sleep.
*/
queue.sma = sma;
queue.sops = sops;
queue.nsops = nsops;
queue.undo = un;
queue.pid = current->pid;
queue.alter = decrease;
queue.id = semid;
if (alter)
append_to_queue(sma ,&queue);
else
prepend_to_queue(sma ,&queue);
current->semsleeping = &queue;
for (;;) {
struct sem_array* tmp;
queue.status = -EINTR;
queue.sleeper = current;
current->state = TASK_INTERRUPTIBLE;
sem_unlock(semid);
schedule();
tmp = sem_lock(semid);
if(tmp==NULL) {
if(queue.prev != NULL)
BUG();
current->semsleeping = NULL;
error = -EIDRM;
goto out_free;
}
/*
* If queue.status == 1 we where woken up and
* have to retry else we simply return.
* If an interrupt occurred we have to clean up the
* queue
*
*/
if (queue.status == 1)
{
error = try_atomic_semop (sma, sops, nsops, un,
current->pid,0);
if (error <= 0)
break;
} else {
error = queue.status;
if (queue.prev) /* got Interrupt */
break;
/* Everything done by update_queue */
current->semsleeping = NULL;
goto out_unlock_free;
}
}
current->semsleeping = NULL;
remove_from_queue(sma,&queue);
update:
if (alter)
update_queue (sma);
out_unlock_free:
sem_unlock(semid);
out_free:
if(sops != fast_sops)
kfree(sops);
return error;
}
/*
* 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 sem_array *sma;
int nsems, i;
/* If the current process was sleeping for a semaphore,
* remove it from the queue.
*/
if ((q = current->semsleeping)) {
int semid = q->id;
sma = sem_lock(semid);
current->semsleeping = NULL;
if (q->prev) {
if(sma==NULL)
BUG();
remove_from_queue(q->sma,q);
}
if(sma!=NULL)
sem_unlock(semid);
}
for (up = ¤t->semundo; (u = *up); *up = u->proc_next, kfree(u)) {
int semid = u->semid;
if(semid == -1)
continue;
sma = sem_lock(semid);
if (sma == NULL)
continue;
if (u->semid == -1)
goto next_entry;
if (sem_checkid(sma,u->semid))
goto next_entry;
/* 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);
goto next_entry;
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);
next_entry:
sem_unlock(semid);
}
current->semundo = NULL;
}
#ifdef CONFIG_PROC_FS
static int sysvipc_sem_read_proc(char *buffer, char **start, off_t offset, int length, int *eof, void *data)
{
off_t pos = 0;
off_t begin = 0;
int i, len = 0;
len += sprintf(buffer, " key semid perms nsems uid gid cuid cgid otime ctime\n");
down(&sem_ids.sem);
for(i = 0; i <= sem_ids.max_id; i++) {
struct sem_array *sma;
sma = sem_lock(i);
if(sma) {
len += sprintf(buffer + len, "%10d %10d %4o %10lu %5u %5u %5u %5u %10lu %10lu\n",
sma->sem_perm.key,
sem_buildid(i,sma->sem_perm.seq),
sma->sem_perm.mode,
sma->sem_nsems,
sma->sem_perm.uid,
sma->sem_perm.gid,
sma->sem_perm.cuid,
sma->sem_perm.cgid,
sma->sem_otime,
sma->sem_ctime);
sem_unlock(i);
pos += len;
if(pos < offset) {
len = 0;
begin = pos;
}
if(pos > offset + length)
goto done;
}
}
*eof = 1;
done:
up(&sem_ids.sem);
*start = buffer + (offset - begin);
len -= (offset - begin);
if(len > length)
len = length;
if(len < 0)
len = 0;
return len;
}
#endif
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