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NetBSD/sys/kern/sysv_sem.c

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/* $NetBSD: sysv_sem.c,v 1.32 1998/10/21 22:24:28 tron Exp $ */
/*
* Implementation of SVID semaphores
*
* Author: Daniel Boulet
*
* This software is provided ``AS IS'' without any warranties of any kind.
*/
#define SYSVSEM
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/proc.h>
#include <sys/sem.h>
#include <sys/malloc.h>
#include <sys/mount.h>
#include <sys/syscallargs.h>
int semtot = 0;
struct proc *semlock_holder = NULL;
#ifdef SEM_DEBUG
#define SEM_PRINTF(a) printf a
#else
#define SEM_PRINTF(a)
#endif
void semlock __P((struct proc *));
struct sem_undo *semu_alloc __P((struct proc *));
int semundo_adjust __P((struct proc *, struct sem_undo **, int, int, int));
void semundo_clear __P((int, int));
void
seminit()
{
register int i;
if (sema == NULL)
panic("sema is NULL");
if (semu == NULL)
panic("semu is NULL");
for (i = 0; i < seminfo.semmni; i++) {
sema[i].sem_base = 0;
sema[i].sem_perm.mode = 0;
}
for (i = 0; i < seminfo.semmnu; i++) {
register struct sem_undo *suptr = SEMU(i);
suptr->un_proc = NULL;
}
semu_list = NULL;
}
void
semlock(p)
struct proc *p;
{
while (semlock_holder != NULL && semlock_holder != p)
sleep((caddr_t)&semlock_holder, (PZERO - 4));
}
/*
* Lock or unlock the entire semaphore facility.
*
* This will probably eventually evolve into a general purpose semaphore
* facility status enquiry mechanism (I don't like the "read /dev/kmem"
* approach currently taken by ipcs and the amount of info that we want
* to be able to extract for ipcs is probably beyond the capability of
* the getkerninfo facility.
*
* At the time that the current version of semconfig was written, ipcs is
* the only user of the semconfig facility. It uses it to ensure that the
* semaphore facility data structures remain static while it fishes around
* in /dev/kmem.
*/
int
sys_semconfig(p, v, retval)
struct proc *p;
void *v;
register_t *retval;
{
struct sys_semconfig_args /* {
syscallarg(int) flag;
} */ *uap = v;
int eval = 0;
semlock(p);
switch (SCARG(uap, flag)) {
case SEM_CONFIG_FREEZE:
semlock_holder = p;
break;
case SEM_CONFIG_THAW:
semlock_holder = NULL;
wakeup((caddr_t)&semlock_holder);
break;
default:
printf(
"semconfig: unknown flag parameter value (%d) - ignored\n",
SCARG(uap, flag));
eval = EINVAL;
break;
}
*retval = 0;
return(eval);
}
/*
* Allocate a new sem_undo structure for a process
* (returns ptr to structure or NULL if no more room)
*/
struct sem_undo *
semu_alloc(p)
struct proc *p;
{
register int i;
register struct sem_undo *suptr;
register struct sem_undo **supptr;
int attempt;
/*
* Try twice to allocate something.
* (we'll purge any empty structures after the first pass so
* two passes are always enough)
*/
for (attempt = 0; attempt < 2; attempt++) {
/*
* Look for a free structure.
* Fill it in and return it if we find one.
*/
for (i = 0; i < seminfo.semmnu; i++) {
suptr = SEMU(i);
if (suptr->un_proc == NULL) {
suptr->un_next = semu_list;
semu_list = suptr;
suptr->un_cnt = 0;
suptr->un_proc = p;
return(suptr);
}
}
/*
* We didn't find a free one, if this is the first attempt
* then try to free some structures.
*/
if (attempt == 0) {
/* All the structures are in use - try to free some */
int did_something = 0;
supptr = &semu_list;
while ((suptr = *supptr) != NULL) {
if (suptr->un_cnt == 0) {
suptr->un_proc = NULL;
*supptr = suptr->un_next;
did_something = 1;
} else
supptr = &(suptr->un_next);
}
/* If we didn't free anything then just give-up */
if (!did_something)
return(NULL);
} else {
/*
* The second pass failed even though we freed
* something after the first pass!
* This is IMPOSSIBLE!
*/
panic("semu_alloc - second attempt failed");
}
}
return NULL;
}
/*
* Adjust a particular entry for a particular proc
*/
int
semundo_adjust(p, supptr, semid, semnum, adjval)
register struct proc *p;
struct sem_undo **supptr;
int semid, semnum;
int adjval;
{
register struct sem_undo *suptr;
register struct undo *sunptr;
int i;
/* Look for and remember the sem_undo if the caller doesn't provide
it */
suptr = *supptr;
if (suptr == NULL) {
for (suptr = semu_list; suptr != NULL; suptr = suptr->un_next) {
if (suptr->un_proc == p) {
*supptr = suptr;
break;
}
}
if (suptr == NULL) {
if (adjval == 0)
return(0);
suptr = semu_alloc(p);
if (suptr == NULL)
return(ENOSPC);
*supptr = suptr;
}
}
/*
* Look for the requested entry and adjust it (delete if adjval becomes
* 0).
*/
sunptr = &suptr->un_ent[0];
for (i = 0; i < suptr->un_cnt; i++, sunptr++) {
if (sunptr->un_id != semid || sunptr->un_num != semnum)
continue;
if (adjval == 0)
sunptr->un_adjval = 0;
else
sunptr->un_adjval += adjval;
if (sunptr->un_adjval == 0) {
suptr->un_cnt--;
if (i < suptr->un_cnt)
suptr->un_ent[i] =
suptr->un_ent[suptr->un_cnt];
}
return(0);
}
/* Didn't find the right entry - create it */
if (adjval == 0)
return(0);
if (suptr->un_cnt == SEMUME)
return(EINVAL);
sunptr = &suptr->un_ent[suptr->un_cnt];
suptr->un_cnt++;
sunptr->un_adjval = adjval;
sunptr->un_id = semid;
sunptr->un_num = semnum;
return(0);
}
void
semundo_clear(semid, semnum)
int semid, semnum;
{
register struct sem_undo *suptr;
for (suptr = semu_list; suptr != NULL; suptr = suptr->un_next) {
register struct undo *sunptr;
register int i;
sunptr = &suptr->un_ent[0];
for (i = 0; i < suptr->un_cnt; i++, sunptr++) {
if (sunptr->un_id == semid) {
if (semnum == -1 || sunptr->un_num == semnum) {
suptr->un_cnt--;
if (i < suptr->un_cnt) {
suptr->un_ent[i] =
suptr->un_ent[suptr->un_cnt];
i--, sunptr--;
}
}
if (semnum != -1)
break;
}
}
}
}
int
sys___semctl(p, v, retval)
struct proc *p;
register void *v;
register_t *retval;
{
register struct sys___semctl_args /* {
syscallarg(int) semid;
syscallarg(int) semnum;
syscallarg(int) cmd;
syscallarg(union semun *) arg;
} */ *uap = v;
int semid = SCARG(uap, semid);
int semnum = SCARG(uap, semnum);
int cmd = SCARG(uap, cmd);
union semun *arg = SCARG(uap, arg);
union semun real_arg;
struct ucred *cred = p->p_ucred;
int i, rval, eval;
struct semid_ds sbuf;
register struct semid_ds *semaptr;
SEM_PRINTF(("call to semctl(%d, %d, %d, %p)\n",
semid, semnum, cmd, arg));
semlock(p);
semid = IPCID_TO_IX(semid);
if (semid < 0 || semid >= seminfo.semmsl)
return(EINVAL);
semaptr = &sema[semid];
if ((semaptr->sem_perm.mode & SEM_ALLOC) == 0 ||
semaptr->sem_perm.seq != IPCID_TO_SEQ(SCARG(uap, semid)))
return(EINVAL);
eval = 0;
rval = 0;
switch (cmd) {
case IPC_RMID:
if ((eval = ipcperm(cred, &semaptr->sem_perm, IPC_M)) != 0)
return(eval);
semaptr->sem_perm.cuid = cred->cr_uid;
semaptr->sem_perm.uid = cred->cr_uid;
semtot -= semaptr->sem_nsems;
for (i = semaptr->sem_base - sem; i < semtot; i++)
sem[i] = sem[i + semaptr->sem_nsems];
for (i = 0; i < seminfo.semmni; i++) {
if ((sema[i].sem_perm.mode & SEM_ALLOC) &&
sema[i].sem_base > semaptr->sem_base)
sema[i].sem_base -= semaptr->sem_nsems;
}
semaptr->sem_perm.mode = 0;
semundo_clear(semid, -1);
wakeup((caddr_t)semaptr);
break;
case IPC_SET:
if ((eval = ipcperm(cred, &semaptr->sem_perm, IPC_M)))
return(eval);
if ((eval = copyin(arg, &real_arg, sizeof(real_arg))) != 0)
return(eval);
if ((eval = copyin(real_arg.buf, (caddr_t)&sbuf,
sizeof(sbuf))) != 0)
return(eval);
semaptr->sem_perm.uid = sbuf.sem_perm.uid;
semaptr->sem_perm.gid = sbuf.sem_perm.gid;
semaptr->sem_perm.mode = (semaptr->sem_perm.mode & ~0777) |
(sbuf.sem_perm.mode & 0777);
semaptr->sem_ctime = time.tv_sec;
break;
case IPC_STAT:
if ((eval = ipcperm(cred, &semaptr->sem_perm, IPC_R)))
return(eval);
if ((eval = copyin(arg, &real_arg, sizeof(real_arg))) != 0)
return(eval);
eval = copyout((caddr_t)semaptr, real_arg.buf,
sizeof(struct semid_ds));
break;
case GETNCNT:
if ((eval = ipcperm(cred, &semaptr->sem_perm, IPC_R)))
return(eval);
if (semnum < 0 || semnum >= semaptr->sem_nsems)
return(EINVAL);
rval = semaptr->sem_base[semnum].semncnt;
break;
case GETPID:
if ((eval = ipcperm(cred, &semaptr->sem_perm, IPC_R)))
return(eval);
if (semnum < 0 || semnum >= semaptr->sem_nsems)
return(EINVAL);
rval = semaptr->sem_base[semnum].sempid;
break;
case GETVAL:
if ((eval = ipcperm(cred, &semaptr->sem_perm, IPC_R)))
return(eval);
if (semnum < 0 || semnum >= semaptr->sem_nsems)
return(EINVAL);
rval = semaptr->sem_base[semnum].semval;
break;
case GETALL:
if ((eval = ipcperm(cred, &semaptr->sem_perm, IPC_R)))
return(eval);
if ((eval = copyin(arg, &real_arg, sizeof(real_arg))) != 0)
return(eval);
for (i = 0; i < semaptr->sem_nsems; i++) {
eval = copyout((caddr_t)&semaptr->sem_base[i].semval,
&real_arg.array[i], sizeof(real_arg.array[0]));
if (eval != 0)
break;
}
break;
case GETZCNT:
if ((eval = ipcperm(cred, &semaptr->sem_perm, IPC_R)))
return(eval);
if (semnum < 0 || semnum >= semaptr->sem_nsems)
return(EINVAL);
rval = semaptr->sem_base[semnum].semzcnt;
break;
case SETVAL:
if ((eval = ipcperm(cred, &semaptr->sem_perm, IPC_W)))
return(eval);
if (semnum < 0 || semnum >= semaptr->sem_nsems)
return(EINVAL);
if ((eval = copyin(arg, &real_arg, sizeof(real_arg))) != 0)
return(eval);
semaptr->sem_base[semnum].semval = real_arg.val;
semundo_clear(semid, semnum);
wakeup((caddr_t)semaptr);
break;
case SETALL:
if ((eval = ipcperm(cred, &semaptr->sem_perm, IPC_W)))
return(eval);
if ((eval = copyin(arg, &real_arg, sizeof(real_arg))) != 0)
return(eval);
for (i = 0; i < semaptr->sem_nsems; i++) {
eval = copyin(&real_arg.array[i],
(caddr_t)&semaptr->sem_base[i].semval,
sizeof(real_arg.array[0]));
if (eval != 0)
break;
}
semundo_clear(semid, -1);
wakeup((caddr_t)semaptr);
break;
default:
return(EINVAL);
}
if (eval == 0)
*retval = rval;
return(eval);
}
int
sys_semget(p, v, retval)
struct proc *p;
void *v;
register_t *retval;
{
register struct sys_semget_args /* {
syscallarg(key_t) key;
syscallarg(int) nsems;
syscallarg(int) semflg;
} */ *uap = v;
int semid, eval;
int key = SCARG(uap, key);
int nsems = SCARG(uap, nsems);
int semflg = SCARG(uap, semflg);
struct ucred *cred = p->p_ucred;
SEM_PRINTF(("semget(0x%x, %d, 0%o)\n", key, nsems, semflg));
semlock(p);
if (key != IPC_PRIVATE) {
for (semid = 0; semid < seminfo.semmni; semid++) {
if ((sema[semid].sem_perm.mode & SEM_ALLOC) &&
sema[semid].sem_perm.key == key)
break;
}
if (semid < seminfo.semmni) {
SEM_PRINTF(("found public key\n"));
if ((eval = ipcperm(cred, &sema[semid].sem_perm,
semflg & 0700)))
return(eval);
if (nsems > 0 && sema[semid].sem_nsems < nsems) {
SEM_PRINTF(("too small\n"));
return(EINVAL);
}
if ((semflg & IPC_CREAT) && (semflg & IPC_EXCL)) {
SEM_PRINTF(("not exclusive\n"));
return(EEXIST);
}
goto found;
}
}
SEM_PRINTF(("need to allocate the semid_ds\n"));
if (key == IPC_PRIVATE || (semflg & IPC_CREAT)) {
if (nsems <= 0 || nsems > seminfo.semmsl) {
SEM_PRINTF(("nsems out of range (0<%d<=%d)\n", nsems,
seminfo.semmsl));
return(EINVAL);
}
if (nsems > seminfo.semmns - semtot) {
SEM_PRINTF(("not enough semaphores left (need %d, got %d)\n",
nsems, seminfo.semmns - semtot));
return(ENOSPC);
}
for (semid = 0; semid < seminfo.semmni; semid++) {
if ((sema[semid].sem_perm.mode & SEM_ALLOC) == 0)
break;
}
if (semid == seminfo.semmni) {
SEM_PRINTF(("no more semid_ds's available\n"));
return(ENOSPC);
}
SEM_PRINTF(("semid %d is available\n", semid));
sema[semid].sem_perm.key = key;
sema[semid].sem_perm.cuid = cred->cr_uid;
sema[semid].sem_perm.uid = cred->cr_uid;
sema[semid].sem_perm.cgid = cred->cr_gid;
sema[semid].sem_perm.gid = cred->cr_gid;
sema[semid].sem_perm.mode = (semflg & 0777) | SEM_ALLOC;
sema[semid].sem_perm.seq =
(sema[semid].sem_perm.seq + 1) & 0x7fff;
sema[semid].sem_nsems = nsems;
sema[semid].sem_otime = 0;
sema[semid].sem_ctime = time.tv_sec;
sema[semid].sem_base = &sem[semtot];
semtot += nsems;
memset(sema[semid].sem_base, 0,
sizeof(sema[semid].sem_base[0])*nsems);
SEM_PRINTF(("sembase = %p, next = %p\n", sema[semid].sem_base,
&sem[semtot]));
} else {
SEM_PRINTF(("didn't find it and wasn't asked to create it\n"));
return(ENOENT);
}
found:
*retval = IXSEQ_TO_IPCID(semid, sema[semid].sem_perm);
return(0);
}
int
sys_semop(p, v, retval)
struct proc *p;
void *v;
register_t *retval;
{
register struct sys_semop_args /* {
syscallarg(int) semid;
syscallarg(struct sembuf *) sops;
syscallarg(size_t) nsops;
} */ *uap = v;
int semid = SCARG(uap, semid);
int nsops = SCARG(uap, nsops);
struct sembuf sops[MAX_SOPS];
register struct semid_ds *semaptr;
register struct sembuf *sopptr = NULL;
register struct sem *semptr = NULL;
struct sem_undo *suptr = NULL;
struct ucred *cred = p->p_ucred;
int i, j, eval;
int do_wakeup, do_undos;
SEM_PRINTF(("call to semop(%d, %p, %d)\n", semid, sops, nsops));
semlock(p);
semid = IPCID_TO_IX(semid); /* Convert back to zero origin */
if (semid < 0 || semid >= seminfo.semmsl)
return(EINVAL);
semaptr = &sema[semid];
if ((semaptr->sem_perm.mode & SEM_ALLOC) == 0 ||
semaptr->sem_perm.seq != IPCID_TO_SEQ(SCARG(uap, semid)))
return(EINVAL);
if ((eval = ipcperm(cred, &semaptr->sem_perm, IPC_W))) {
SEM_PRINTF(("eval = %d from ipaccess\n", eval));
return(eval);
}
if (nsops > MAX_SOPS) {
SEM_PRINTF(("too many sops (max=%d, nsops=%d)\n", MAX_SOPS, nsops));
return(E2BIG);
}
if ((eval = copyin(SCARG(uap, sops), sops, nsops * sizeof(sops[0])))
!= 0) {
SEM_PRINTF(("eval = %d from copyin(%p, %p, %d)\n", eval,
SCARG(uap, sops), &sops, nsops * sizeof(sops[0])));
return(eval);
}
/*
* Loop trying to satisfy the vector of requests.
* If we reach a point where we must wait, any requests already
* performed are rolled back and we go to sleep until some other
* process wakes us up. At this point, we start all over again.
*
* This ensures that from the perspective of other tasks, a set
* of requests is atomic (never partially satisfied).
*/
do_undos = 0;
for (;;) {
do_wakeup = 0;
for (i = 0; i < nsops; i++) {
sopptr = &sops[i];
if (sopptr->sem_num >= semaptr->sem_nsems)
return(EFBIG);
semptr = &semaptr->sem_base[sopptr->sem_num];
SEM_PRINTF(("semop: semaptr=%x, sem_base=%x, semptr=%x, sem[%d]=%d : op=%d, flag=%s\n",
semaptr, semaptr->sem_base, semptr,
sopptr->sem_num, semptr->semval, sopptr->sem_op,
(sopptr->sem_flg & IPC_NOWAIT) ? "nowait" : "wait"));
if (sopptr->sem_op < 0) {
if ((int)(semptr->semval +
sopptr->sem_op) < 0) {
SEM_PRINTF(("semop: can't do it now\n"));
break;
} else {
semptr->semval += sopptr->sem_op;
if (semptr->semval == 0 &&
semptr->semzcnt > 0)
do_wakeup = 1;
}
if (sopptr->sem_flg & SEM_UNDO)
do_undos = 1;
} else if (sopptr->sem_op == 0) {
if (semptr->semval > 0) {
SEM_PRINTF(("semop: not zero now\n"));
break;
}
} else {
if (semptr->semncnt > 0)
do_wakeup = 1;
semptr->semval += sopptr->sem_op;
if (sopptr->sem_flg & SEM_UNDO)
do_undos = 1;
}
}
/*
* Did we get through the entire vector?
*/
if (i >= nsops)
goto done;
/*
* No ... rollback anything that we've already done
*/
SEM_PRINTF(("semop: rollback 0 through %d\n", i-1));
for (j = 0; j < i; j++)
semaptr->sem_base[sops[j].sem_num].semval -=
sops[j].sem_op;
/*
* If the request that we couldn't satisfy has the
* NOWAIT flag set then return with EAGAIN.
*/
if (sopptr->sem_flg & IPC_NOWAIT)
return(EAGAIN);
if (sopptr->sem_op == 0)
semptr->semzcnt++;
else
semptr->semncnt++;
SEM_PRINTF(("semop: good night!\n"));
eval = tsleep((caddr_t)semaptr, (PZERO - 4) | PCATCH,
"semwait", 0);
SEM_PRINTF(("semop: good morning (eval=%d)!\n", eval));
suptr = NULL; /* sem_undo may have been reallocated */
if (eval != 0)
return(EINTR);
SEM_PRINTF(("semop: good morning!\n"));
/*
* Make sure that the semaphore still exists
*/
if ((semaptr->sem_perm.mode & SEM_ALLOC) == 0 ||
semaptr->sem_perm.seq != IPCID_TO_SEQ(SCARG(uap, semid))) {
/* The man page says to return EIDRM. */
/* Unfortunately, BSD doesn't define that code! */
#ifdef EIDRM
return(EIDRM);
#else
return(EINVAL);
#endif
}
/*
* The semaphore is still alive. Readjust the count of
* waiting processes.
*/
if (sopptr->sem_op == 0)
semptr->semzcnt--;
else
semptr->semncnt--;
}
done:
/*
* Process any SEM_UNDO requests.
*/
if (do_undos) {
for (i = 0; i < nsops; i++) {
/*
* We only need to deal with SEM_UNDO's for non-zero
* op's.
*/
int adjval;
if ((sops[i].sem_flg & SEM_UNDO) == 0)
continue;
adjval = sops[i].sem_op;
if (adjval == 0)
continue;
eval = semundo_adjust(p, &suptr, semid,
sops[i].sem_num, -adjval);
if (eval == 0)
continue;
/*
* Oh-Oh! We ran out of either sem_undo's or undo's.
* Rollback the adjustments to this point and then
* rollback the semaphore ups and down so we can return
* with an error with all structures restored. We
* rollback the undo's in the exact reverse order that
* we applied them. This guarantees that we won't run
* out of space as we roll things back out.
*/
for (j = i - 1; j >= 0; j--) {
if ((sops[j].sem_flg & SEM_UNDO) == 0)
continue;
adjval = sops[j].sem_op;
if (adjval == 0)
continue;
if (semundo_adjust(p, &suptr, semid,
sops[j].sem_num, adjval) != 0)
panic("semop - can't undo undos");
}
for (j = 0; j < nsops; j++)
semaptr->sem_base[sops[j].sem_num].semval -=
sops[j].sem_op;
SEM_PRINTF(("eval = %d from semundo_adjust\n", eval));
return(eval);
} /* loop through the sops */
} /* if (do_undos) */
/* We're definitely done - set the sempid's */
for (i = 0; i < nsops; i++) {
sopptr = &sops[i];
semptr = &semaptr->sem_base[sopptr->sem_num];
semptr->sempid = p->p_pid;
}
/* Do a wakeup if any semaphore was up'd. */
if (do_wakeup) {
SEM_PRINTF(("semop: doing wakeup\n"));
#ifdef SEM_WAKEUP
sem_wakeup((caddr_t)semaptr);
#else
wakeup((caddr_t)semaptr);
#endif
SEM_PRINTF(("semop: back from wakeup\n"));
}
SEM_PRINTF(("semop: done\n"));
*retval = 0;
return(0);
}
/*
* Go through the undo structures for this process and apply the adjustments to
* semaphores.
*/
void
semexit(p)
struct proc *p;
{
register struct sem_undo *suptr;
register struct sem_undo **supptr;
/*
* Go through the chain of undo vectors looking for one associated with
* this process.
*/
for (supptr = &semu_list; (suptr = *supptr) != NULL;
supptr = &suptr->un_next) {
if (suptr->un_proc == p)
break;
}
/*
* There are a few possibilities to consider here ...
*
* 1) The semaphore facility isn't currently locked. In this case,
* this call should proceed normally.
* 2) The semaphore facility is locked by this process (i.e. the one
* that is exiting). In this case, this call should proceed as
* usual and the facility should be unlocked at the end of this
* routine (since the locker is exiting).
* 3) The semaphore facility is locked by some other process and this
* process doesn't have an undo structure allocated for it. In this
* case, this call should proceed normally (i.e. not accomplish
* anything and, most importantly, not block since that is
* unnecessary and could result in a LOT of processes blocking in
* here if the facility is locked for a long time).
* 4) The semaphore facility is locked by some other process and this
* process has an undo structure allocated for it. In this case,
* this call should block until the facility has been unlocked since
* the holder of the lock may be examining this process's proc entry
* (the ipcs utility does this when printing out the information
* from the allocated sem undo elements).
*
* This leads to the conclusion that we should not block unless we
* discover that the someone else has the semaphore facility locked and
* this process has an undo structure. Let's do that...
*
* Note that we do this in a separate pass from the one that processes
* any existing undo structure since we don't want to risk blocking at
* that time (it would make the actual unlinking of the element from
* the chain of allocated undo structures rather messy).
*/
/*
* Does someone else hold the semaphore facility's lock?
*/
if (semlock_holder != NULL && semlock_holder != p) {
/*
* Yes (i.e. we are in case 3 or 4).
*
* If we didn't find an undo vector associated with this
* process than we can just return (i.e. we are in case 3).
*
* Note that we know that someone else is holding the lock so
* we don't even have to see if we're holding it...
*/
if (suptr == NULL)
return;
/*
* We are in case 4.
*
* Go to sleep as long as someone else is locking the semaphore
* facility (note that we won't get here if we are holding the
* lock so we don't need to check for that possibility).
*/
while (semlock_holder != NULL)
sleep((caddr_t)&semlock_holder, (PZERO - 4));
/*
* Nobody is holding the facility (i.e. we are now in case 1).
* We can proceed safely according to the argument outlined
* above.
*
* We look up the undo vector again, in case the list changed
* while we were asleep, and the parent is now different.
*/
for (supptr = &semu_list; (suptr = *supptr) != NULL;
supptr = &suptr->un_next) {
if (suptr->un_proc == p)
break;
}
if (suptr == NULL)
panic("semexit: undo vector disappeared");
} else {
/*
* No (i.e. we are in case 1 or 2).
*
* If there is no undo vector, skip to the end and unlock the
* semaphore facility if necessary.
*/
if (suptr == NULL)
goto unlock;
}
/*
* We are now in case 1 or 2, and we have an undo vector for this
* process.
*/
SEM_PRINTF(("proc @%p has undo structure with %d entries\n", p,
suptr->un_cnt));
/*
* If there are any active undo elements then process them.
*/
if (suptr->un_cnt > 0) {
int ix;
for (ix = 0; ix < suptr->un_cnt; ix++) {
int semid = suptr->un_ent[ix].un_id;
int semnum = suptr->un_ent[ix].un_num;
int adjval = suptr->un_ent[ix].un_adjval;
struct semid_ds *semaptr;
semaptr = &sema[semid];
if ((semaptr->sem_perm.mode & SEM_ALLOC) == 0)
panic("semexit - semid not allocated");
if (semnum >= semaptr->sem_nsems)
panic("semexit - semnum out of range");
SEM_PRINTF(("semexit: %p id=%d num=%d(adj=%d) ; sem=%d\n",
suptr->un_proc, suptr->un_ent[ix].un_id,
suptr->un_ent[ix].un_num,
suptr->un_ent[ix].un_adjval,
semaptr->sem_base[semnum].semval));
if (adjval < 0 &&
semaptr->sem_base[semnum].semval < -adjval)
semaptr->sem_base[semnum].semval = 0;
else
semaptr->sem_base[semnum].semval += adjval;
#ifdef SEM_WAKEUP
sem_wakeup((caddr_t)semaptr);
#else
wakeup((caddr_t)semaptr);
#endif
SEM_PRINTF(("semexit: back from wakeup\n"));
}
}
/*
* Deallocate the undo vector.
*/
SEM_PRINTF(("removing vector\n"));
suptr->un_proc = NULL;
*supptr = suptr->un_next;
unlock:
/*
* If the exiting process is holding the global semaphore facility
* lock (i.e. we are in case 2) then release it.
*/
if (semlock_holder == p) {
semlock_holder = NULL;
wakeup((caddr_t)&semlock_holder);
}
}
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