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plan9fox/sys/src/9/port/sysproc.c
cinap_lenrek 3e567afed5 kernel: fix sysexec() error handling compiler problem, sysrendez() busyloop 
the variables elem and file0 and commited are explicitely
set to avoid that they get freed in ther waserror() handlers.

but it turns out the compiler optimizes this out as he
thinks the variables arent used any further. (the compiler
is not aware of the waserror() / longjmp() semantics).

rearrange the code to account for this. instead of using
a local variable to check for point of no return (commited),
we use up->seg[SSEG] to figure it out.

for file0 and elem, we just rearrange the code. elem can be
checked in the error handler if it was already assigned to
up->text, and file0 is just free()'d after the poperror().

remove silly busy loop in sysrendez. it is not needed.
dequeueproc() will make sure that the process has come to
rest.
2013-05-27 00:59:43 +02:00

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#include "u.h"
#include "tos.h"
#include "../port/lib.h"
#include "mem.h"
#include "dat.h"
#include "fns.h"
#include "../port/error.h"
#include "edf.h"
#include <a.out.h>
int shargs(char*, int, char**);
extern void checkpages(void);
extern void checkpagerefs(void);
long
sysr1(ulong*)
{
checkpagerefs();
return 0;
}
long
sysrfork(ulong *arg)
{
Proc *p;
int n, i;
Fgrp *ofg;
Pgrp *opg;
Rgrp *org;
Egrp *oeg;
ulong pid, flag;
Mach *wm;
flag = arg[0];
/* Check flags before we commit */
if((flag & (RFFDG|RFCFDG)) == (RFFDG|RFCFDG))
error(Ebadarg);
if((flag & (RFNAMEG|RFCNAMEG)) == (RFNAMEG|RFCNAMEG))
error(Ebadarg);
if((flag & (RFENVG|RFCENVG)) == (RFENVG|RFCENVG))
error(Ebadarg);
if((flag&RFPROC) == 0) {
if(flag & (RFMEM|RFNOWAIT))
error(Ebadarg);
if(flag & (RFFDG|RFCFDG)) {
ofg = up->fgrp;
if(flag & RFFDG)
up->fgrp = dupfgrp(ofg);
else
up->fgrp = dupfgrp(nil);
closefgrp(ofg);
}
if(flag & (RFNAMEG|RFCNAMEG)) {
opg = up->pgrp;
up->pgrp = newpgrp();
if(flag & RFNAMEG)
pgrpcpy(up->pgrp, opg);
/* inherit noattach */
up->pgrp->noattach = opg->noattach;
closepgrp(opg);
}
if(flag & RFNOMNT)
up->pgrp->noattach = 1;
if(flag & RFREND) {
org = up->rgrp;
up->rgrp = newrgrp();
closergrp(org);
}
if(flag & (RFENVG|RFCENVG)) {
oeg = up->egrp;
up->egrp = smalloc(sizeof(Egrp));
up->egrp->ref = 1;
if(flag & RFENVG)
envcpy(up->egrp, oeg);
closeegrp(oeg);
}
if(flag & RFNOTEG)
up->noteid = pidalloc(0);
return 0;
}
p = newproc();
p->scallnr = up->scallnr;
p->s = up->s;
p->nerrlab = 0;
p->slash = up->slash;
p->dot = up->dot;
incref(p->dot);
memmove(p->note, up->note, sizeof(p->note));
p->privatemem = up->privatemem;
p->noswap = up->noswap;
p->nnote = up->nnote;
p->notified = 0;
p->lastnote = up->lastnote;
p->notify = up->notify;
p->ureg = up->ureg;
p->dbgreg = 0;
/* Make a new set of memory segments */
n = flag & RFMEM;
qlock(&p->seglock);
if(waserror()){
qunlock(&p->seglock);
nexterror();
}
for(i = 0; i < NSEG; i++)
if(up->seg[i])
p->seg[i] = dupseg(up->seg, i, n);
qunlock(&p->seglock);
poperror();
/* File descriptors */
if(flag & (RFFDG|RFCFDG)) {
if(flag & RFFDG)
p->fgrp = dupfgrp(up->fgrp);
else
p->fgrp = dupfgrp(nil);
}
else {
p->fgrp = up->fgrp;
incref(p->fgrp);
}
/* Process groups */
if(flag & (RFNAMEG|RFCNAMEG)) {
p->pgrp = newpgrp();
if(flag & RFNAMEG)
pgrpcpy(p->pgrp, up->pgrp);
/* inherit noattach */
p->pgrp->noattach = up->pgrp->noattach;
}
else {
p->pgrp = up->pgrp;
incref(p->pgrp);
}
if(flag & RFNOMNT)
p->pgrp->noattach = 1;
if(flag & RFREND)
p->rgrp = newrgrp();
else {
incref(up->rgrp);
p->rgrp = up->rgrp;
}
/* Environment group */
if(flag & (RFENVG|RFCENVG)) {
p->egrp = smalloc(sizeof(Egrp));
p->egrp->ref = 1;
if(flag & RFENVG)
envcpy(p->egrp, up->egrp);
}
else {
p->egrp = up->egrp;
incref(p->egrp);
}
p->hang = up->hang;
p->procmode = up->procmode;
if(up->procctl == Proc_tracesyscall)
p->procctl = Proc_tracesyscall;
/* Craft a return frame which will cause the child to pop out of
* the scheduler in user mode with the return register zero
*/
forkchild(p, up->dbgreg);
p->parent = up;
if((flag&RFNOWAIT) == 0){
p->parentpid = up->pid;
lock(&up->exl);
up->nchild++;
unlock(&up->exl);
}
if((flag&RFNOTEG) == 0)
p->noteid = up->noteid;
pid = p->pid;
memset(p->time, 0, sizeof(p->time));
p->time[TReal] = MACHP(0)->ticks;
kstrdup(&p->text, up->text);
kstrdup(&p->user, up->user);
procfork(p);
/*
* since the bss/data segments are now shareable,
* any mmu info about this process is now stale
* (i.e. has bad properties) and has to be discarded.
*/
flushmmu();
p->basepri = up->basepri;
p->priority = up->basepri;
p->fixedpri = up->fixedpri;
p->mp = up->mp;
wm = up->wired;
if(wm)
procwired(p, wm->machno);
ready(p);
sched();
return pid;
}
static ulong
l2be(long l)
{
uchar *cp;
cp = (uchar*)&l;
return (cp[0]<<24) | (cp[1]<<16) | (cp[2]<<8) | cp[3];
}
long
sysexec(ulong *arg)
{
Segment *s, *ts;
ulong t, d, b;
int i;
Chan *tc;
char **argv, **argp;
char *a, *charp, *args, *file, *file0;
char *progarg[sizeof(Exec)/2+1], *elem, progelem[64];
ulong ssize, tstk, nargs, nbytes, n, bssend;
int indir;
Exec exec;
char line[sizeof(Exec)];
Fgrp *f;
Image *img;
ulong magic, text, entry, data, bss;
Tos *tos;
indir = 0;
elem = nil;
validaddr(arg[0], 1, 0);
file0 = validnamedup((char*)arg[0], 1);
if(waserror()){
free(file0);
if(elem != up->text)
free(elem);
/* Disaster after commit */
if(!up->seg[SSEG])
pexit(up->errstr, 1);
nexterror();
}
file = file0;
for(;;){
tc = namec(file, Aopen, OEXEC, 0);
if(waserror()){
cclose(tc);
nexterror();
}
if(!indir)
kstrdup(&elem, up->genbuf);
n = devtab[tc->type]->read(tc, &exec, sizeof(Exec), 0);
if(n < 2)
error(Ebadexec);
magic = l2be(exec.magic);
text = l2be(exec.text);
entry = l2be(exec.entry);
if(n==sizeof(Exec) && (magic == AOUT_MAGIC)){
if(text >= USTKTOP-UTZERO
|| entry < UTZERO+sizeof(Exec)
|| entry >= UTZERO+sizeof(Exec)+text)
error(Ebadexec);
break; /* for binary */
}
/*
* Process #! /bin/sh args ...
*/
memmove(line, &exec, sizeof(Exec));
if(indir || line[0]!='#' || line[1]!='!')
error(Ebadexec);
n = shargs(line, n, progarg);
if(n == 0)
error(Ebadexec);
indir = 1;
/*
* First arg becomes complete file name
*/
progarg[n++] = file;
progarg[n] = 0;
validaddr(arg[1], BY2WD, 1);
arg[1] += BY2WD;
file = progarg[0];
if(strlen(elem) >= sizeof progelem)
error(Ebadexec);
strcpy(progelem, elem);
progarg[0] = progelem;
poperror();
cclose(tc);
}
data = l2be(exec.data);
bss = l2be(exec.bss);
t = (UTZERO+sizeof(Exec)+text+(BY2PG-1)) & ~(BY2PG-1);
d = (t + data + (BY2PG-1)) & ~(BY2PG-1);
bssend = t + data + bss;
b = (bssend + (BY2PG-1)) & ~(BY2PG-1);
if(t >= KZERO || d >= KZERO || b >= KZERO)
error(Ebadexec);
/*
* Args: pass 1: count
*/
nbytes = sizeof(Tos); /* hole for profiling clock at top of stack (and more) */
nargs = 0;
if(indir){
argp = progarg;
while(*argp){
a = *argp++;
nbytes += strlen(a) + 1;
nargs++;
}
}
evenaddr(arg[1]);
argp = (char**)arg[1];
validaddr((ulong)argp, BY2WD, 0);
while(*argp){
a = *argp++;
if(((ulong)argp&(BY2PG-1)) < BY2WD)
validaddr((ulong)argp, BY2WD, 0);
validaddr((ulong)a, 1, 0);
nbytes += ((char*)vmemchr(a, 0, 0x7FFFFFFF) - a) + 1;
nargs++;
}
ssize = BY2WD*(nargs+1) + ((nbytes+(BY2WD-1)) & ~(BY2WD-1));
/*
* 8-byte align SP for those (e.g. sparc) that need it.
* execregs() will subtract another 4 bytes for argc.
*/
if((ssize+4) & 7)
ssize += 4;
if(PGROUND(ssize) >= USTKSIZE)
error(Enovmem);
/*
* Build the stack segment, putting it in kernel virtual for the moment
*/
qlock(&up->seglock);
if(waserror()){
qunlock(&up->seglock);
nexterror();
}
s = up->seg[SSEG];
do {
tstk = s->base;
if(tstk <= USTKSIZE)
error(Enovmem);
} while((s = isoverlap(up, tstk-USTKSIZE, USTKSIZE)) != nil);
up->seg[ESEG] = newseg(SG_STACK, tstk-USTKSIZE, USTKSIZE/BY2PG);
/*
* Args: pass 2: assemble; the pages will be faulted in
*/
tos = (Tos*)(tstk - sizeof(Tos));
tos->cyclefreq = m->cyclefreq;
tos->kcycles = 0;
tos->pcycles = 0;
tos->clock = 0;
argv = (char**)(tstk - ssize);
charp = (char*)(tstk - nbytes);
args = charp;
if(indir)
argp = progarg;
else
argp = (char**)arg[1];
for(i=0; i<nargs; i++){
if(indir && *argp==0) {
indir = 0;
argp = (char**)arg[1];
}
*argv++ = charp + (USTKTOP-tstk);
n = strlen(*argp) + 1;
memmove(charp, *argp++, n);
charp += n;
}
free(up->text);
up->text = elem;
/* copy args; easiest from new process's stack */
n = charp - args;
if(n > 128) /* don't waste too much space on huge arg lists */
n = 128;
a = up->args;
up->args = nil;
free(a);
up->args = smalloc(n);
memmove(up->args, args, n);
if(n>0 && up->args[n-1]!='\0'){
/* make sure last arg is NUL-terminated */
/* put NUL at UTF-8 character boundary */
for(i=n-1; i>0; --i)
if(fullrune(up->args+i, n-i))
break;
up->args[i] = 0;
n = i+1;
}
up->nargs = n;
/*
* Committed.
* Free old memory.
* Special segments are maintained across exec
*/
for(i = SSEG; i <= BSEG; i++) {
putseg(up->seg[i]);
/* prevent a second free if we have an error */
up->seg[i] = 0;
}
for(i = ESEG+1; i < NSEG; i++) {
s = up->seg[i];
if(s != 0 && (s->type&SG_CEXEC) != 0) {
putseg(s);
up->seg[i] = 0;
}
}
/*
* Close on exec
*/
if((f = up->fgrp) != nil){
for(i=0; i<=f->maxfd; i++)
fdclose(i, CCEXEC);
}
/* Text. Shared. Attaches to cache image if possible */
/* attachimage returns a locked cache image */
img = attachimage(SG_TEXT|SG_RONLY, tc, UTZERO, (t-UTZERO)>>PGSHIFT);
ts = img->s;
up->seg[TSEG] = ts;
ts->flushme = 1;
ts->fstart = 0;
ts->flen = sizeof(Exec)+text;
unlock(img);
/* Data. Shared. */
s = newseg(SG_DATA, t, (d-t)>>PGSHIFT);
up->seg[DSEG] = s;
/* Attached by hand */
incref(img);
s->image = img;
s->fstart = ts->fstart+ts->flen;
s->flen = data;
/* BSS. Zero fill on demand */
up->seg[BSEG] = newseg(SG_BSS, d, (b-d)>>PGSHIFT);
/*
* Move the stack
*/
s = up->seg[ESEG];
up->seg[ESEG] = 0;
s->base = USTKTOP-USTKSIZE;
s->top = USTKTOP;
relocateseg(s, USTKTOP-tstk);
up->seg[SSEG] = s;
qunlock(&up->seglock);
poperror(); /* seglock */
/*
* '/' processes are higher priority (hack to make /ip more responsive).
*/
if(devtab[tc->type]->dc == L'/')
up->basepri = PriRoot;
up->priority = up->basepri;
poperror(); /* tc */
cclose(tc);
poperror(); /* file0 */
free(file0);
qlock(&up->debug);
up->nnote = 0;
up->notify = 0;
up->notified = 0;
up->privatemem = 0;
procsetup(up);
qunlock(&up->debug);
/*
* At this point, the mmu contains info about the old address
* space and needs to be flushed
*/
flushmmu();
if(up->hang)
up->procctl = Proc_stopme;
return execregs(entry, ssize, nargs);
}
int
shargs(char *s, int n, char **ap)
{
int i;
s += 2;
n -= 2; /* skip #! */
for(i=0; s[i]!='\n'; i++)
if(i == n-1)
return 0;
s[i] = 0;
*ap = 0;
i = 0;
for(;;) {
while(*s==' ' || *s=='\t')
s++;
if(*s == 0)
break;
i++;
*ap++ = s;
*ap = 0;
while(*s && *s!=' ' && *s!='\t')
s++;
if(*s == 0)
break;
else
*s++ = 0;
}
return i;
}
int
return0(void*)
{
return 0;
}
long
syssleep(ulong *arg)
{
int n;
n = arg[0];
if(n <= 0) {
if (up->edf && (up->edf->flags & Admitted))
edfyield();
else
yield();
return 0;
}
if(n < TK2MS(1))
n = TK2MS(1);
tsleep(&up->sleep, return0, 0, n);
return 0;
}
long
sysalarm(ulong *arg)
{
return procalarm(arg[0]);
}
long
sysexits(ulong *arg)
{
char *status;
char *inval = "invalid exit string";
char buf[ERRMAX];
status = (char*)arg[0];
if(status){
if(waserror())
status = inval;
else{
validaddr((ulong)status, 1, 0);
if(vmemchr(status, 0, ERRMAX) == 0){
memmove(buf, status, ERRMAX);
buf[ERRMAX-1] = 0;
status = buf;
}
poperror();
}
}
pexit(status, 1);
return 0; /* not reached */
}
long
sys_wait(ulong *arg)
{
int pid;
Waitmsg w;
OWaitmsg *ow;
if(arg[0] == 0)
return pwait(nil);
validaddr(arg[0], sizeof(OWaitmsg), 1);
evenaddr(arg[0]);
pid = pwait(&w);
if(pid >= 0){
ow = (OWaitmsg*)arg[0];
readnum(0, ow->pid, NUMSIZE, w.pid, NUMSIZE);
readnum(0, ow->time+TUser*NUMSIZE, NUMSIZE, w.time[TUser], NUMSIZE);
readnum(0, ow->time+TSys*NUMSIZE, NUMSIZE, w.time[TSys], NUMSIZE);
readnum(0, ow->time+TReal*NUMSIZE, NUMSIZE, w.time[TReal], NUMSIZE);
strncpy(ow->msg, w.msg, sizeof(ow->msg)-1);
ow->msg[sizeof(ow->msg)-1] = '\0';
}
return pid;
}
long
sysawait(ulong *arg)
{
int i;
int pid;
Waitmsg w;
ulong n;
n = arg[1];
validaddr(arg[0], n, 1);
pid = pwait(&w);
if(pid < 0)
return -1;
i = snprint((char*)arg[0], n, "%d %lud %lud %lud %q",
w.pid,
w.time[TUser], w.time[TSys], w.time[TReal],
w.msg);
return i;
}
void
werrstr(char *fmt, ...)
{
va_list va;
if(up == nil)
return;
va_start(va, fmt);
vseprint(up->syserrstr, up->syserrstr+ERRMAX, fmt, va);
va_end(va);
}
static long
generrstr(char *buf, uint nbuf)
{
char tmp[ERRMAX];
if(nbuf == 0)
error(Ebadarg);
validaddr((ulong)buf, nbuf, 1);
if(nbuf > sizeof tmp)
nbuf = sizeof tmp;
memmove(tmp, buf, nbuf);
/* make sure it's NUL-terminated */
tmp[nbuf-1] = '\0';
memmove(buf, up->syserrstr, nbuf);
buf[nbuf-1] = '\0';
memmove(up->syserrstr, tmp, nbuf);
return 0;
}
long
syserrstr(ulong *arg)
{
return generrstr((char*)arg[0], arg[1]);
}
/* compatibility for old binaries */
long
sys_errstr(ulong *arg)
{
return generrstr((char*)arg[0], 64);
}
long
sysnotify(ulong *arg)
{
if(arg[0] != 0)
validaddr(arg[0], sizeof(ulong), 0);
up->notify = (int(*)(void*, char*))(arg[0]);
return 0;
}
long
sysnoted(ulong *arg)
{
if(arg[0]!=NRSTR && !up->notified)
error(Egreg);
return 0;
}
long
syssegbrk(ulong *arg)
{
int i;
ulong addr;
Segment *s;
addr = arg[0];
for(i = 0; i < NSEG; i++) {
s = up->seg[i];
if(s == 0 || addr < s->base || addr >= s->top)
continue;
switch(s->type&SG_TYPE) {
case SG_TEXT:
case SG_DATA:
case SG_STACK:
error(Ebadarg);
default:
return ibrk(arg[1], i);
}
}
error(Ebadarg);
return 0; /* not reached */
}
long
syssegattach(ulong *arg)
{
return segattach(up, arg[0], (char*)arg[1], arg[2], arg[3]);
}
long
syssegdetach(ulong *arg)
{
int i;
ulong addr;
Segment *s;
qlock(&up->seglock);
if(waserror()){
qunlock(&up->seglock);
nexterror();
}
s = 0;
addr = arg[0];
for(i = 0; i < NSEG; i++)
if(s = up->seg[i]) {
qlock(&s->lk);
if((addr >= s->base && addr < s->top) ||
(s->top == s->base && addr == s->base))
goto found;
qunlock(&s->lk);
}
error(Ebadarg);
found:
/*
* Check we are not detaching the initial stack segment.
*/
if(s == up->seg[SSEG]){
qunlock(&s->lk);
error(Ebadarg);
}
up->seg[i] = 0;
qunlock(&s->lk);
putseg(s);
qunlock(&up->seglock);
poperror();
/* Ensure we flush any entries from the lost segment */
flushmmu();
return 0;
}
long
syssegfree(ulong *arg)
{
Segment *s;
ulong from, to;
from = arg[0];
s = seg(up, from, 1);
if(s == nil)
error(Ebadarg);
to = (from + arg[1]) & ~(BY2PG-1);
from = PGROUND(from);
if(to > s->top) {
qunlock(&s->lk);
error(Ebadarg);
}
mfreeseg(s, from, (to - from) / BY2PG);
qunlock(&s->lk);
flushmmu();
return 0;
}
/* For binary compatibility */
long
sysbrk_(ulong *arg)
{
return ibrk(arg[0], BSEG);
}
long
sysrendezvous(ulong *arg)
{
uintptr tag, val;
Proc *p, **l;
tag = arg[0];
l = &REND(up->rgrp, tag);
lock(up->rgrp);
for(p = *l; p; p = p->rendhash) {
if(p->rendtag == tag) {
*l = p->rendhash;
val = p->rendval;
p->rendval = arg[1];
unlock(up->rgrp);
ready(p);
return val;
}
l = &p->rendhash;
}
/* Going to sleep here */
up->rendtag = tag;
up->rendval = arg[1];
up->rendhash = *l;
*l = up;
up->state = Rendezvous;
unlock(up->rgrp);
sched();
return up->rendval;
}
/*
* The implementation of semaphores is complicated by needing
* to avoid rescheduling in syssemrelease, so that it is safe
* to call from real-time processes. This means syssemrelease
* cannot acquire any qlocks, only spin locks.
*
* Semacquire and semrelease must both manipulate the semaphore
* wait list. Lock-free linked lists only exist in theory, not
* in practice, so the wait list is protected by a spin lock.
*
* The semaphore value *addr is stored in user memory, so it
* cannot be read or written while holding spin locks.
*
* Thus, we can access the list only when holding the lock, and
* we can access the semaphore only when not holding the lock.
* This makes things interesting. Note that sleep's condition function
* is called while holding two locks - r and up->rlock - so it cannot
* access the semaphore value either.
*
* An acquirer announces its intention to try for the semaphore
* by putting a Sema structure onto the wait list and then
* setting Sema.waiting. After one last check of semaphore,
* the acquirer sleeps until Sema.waiting==0. A releaser of n
* must wake up n acquirers who have Sema.waiting set. It does
* this by clearing Sema.waiting and then calling wakeup.
*
* There are three interesting races here.
* The first is that in this particular sleep/wakeup usage, a single
* wakeup can rouse a process from two consecutive sleeps!
* The ordering is:
*
* (a) set Sema.waiting = 1
* (a) call sleep
* (b) set Sema.waiting = 0
* (a) check Sema.waiting inside sleep, return w/o sleeping
* (a) try for semaphore, fail
* (a) set Sema.waiting = 1
* (a) call sleep
* (b) call wakeup(a)
* (a) wake up again
*
* This is okay - semacquire will just go around the loop
* again. It does mean that at the top of the for(;;) loop in
* semacquire, phore.waiting might already be set to 1.
*
* The second is that a releaser might wake an acquirer who is
* interrupted before he can acquire the lock. Since
* release(n) issues only n wakeup calls -- only n can be used
* anyway -- if the interrupted process is not going to use his
* wakeup call he must pass it on to another acquirer.
*
* The third race is similar to the second but more subtle. An
* acquirer sets waiting=1 and then does a final canacquire()
* before going to sleep. The opposite order would result in
* missing wakeups that happen between canacquire and
* waiting=1. (In fact, the whole point of Sema.waiting is to
* avoid missing wakeups between canacquire() and sleep().) But
* there can be spurious wakeups between a successful
* canacquire() and the following semdequeue(). This wakeup is
* not useful to the acquirer, since he has already acquired
* the semaphore. Like in the previous case, though, the
* acquirer must pass the wakeup call along.
*
* This is all rather subtle. The code below has been verified
* with the spin model /sys/src/9/port/semaphore.p. The
* original code anticipated the second race but not the first
* or third, which were caught only with spin. The first race
* is mentioned in /sys/doc/sleep.ps, but I'd forgotten about it.
* It was lucky that my abstract model of sleep/wakeup still managed
* to preserve that behavior.
*
* I remain slightly concerned about memory coherence
* outside of locks. The spin model does not take
* queued processor writes into account so we have to
* think hard. The only variables accessed outside locks
* are the semaphore value itself and the boolean flag
* Sema.waiting. The value is only accessed with cmpswap,
* whose job description includes doing the right thing as
* far as memory coherence across processors. That leaves
* Sema.waiting. To handle it, we call coherence() before each
* read and after each write. - rsc
*/
/* Add semaphore p with addr a to list in seg. */
static void
semqueue(Segment *s, long *a, Sema *p)
{
memset(p, 0, sizeof *p);
p->addr = a;
lock(&s->sema); /* uses s->sema.Rendez.Lock, but no one else is */
p->next = &s->sema;
p->prev = s->sema.prev;
p->next->prev = p;
p->prev->next = p;
unlock(&s->sema);
}
/* Remove semaphore p from list in seg. */
static void
semdequeue(Segment *s, Sema *p)
{
lock(&s->sema);
p->next->prev = p->prev;
p->prev->next = p->next;
unlock(&s->sema);
}
/* Wake up n waiters with addr a on list in seg. */
static void
semwakeup(Segment *s, long *a, long n)
{
Sema *p;
lock(&s->sema);
for(p=s->sema.next; p!=&s->sema && n>0; p=p->next){
if(p->addr == a && p->waiting){
p->waiting = 0;
coherence();
wakeup(p);
n--;
}
}
unlock(&s->sema);
}
/* Add delta to semaphore and wake up waiters as appropriate. */
static long
semrelease(Segment *s, long *addr, long delta)
{
long value;
do
value = *addr;
while(!cmpswap(addr, value, value+delta));
semwakeup(s, addr, delta);
return value+delta;
}
/* Try to acquire semaphore using compare-and-swap */
static int
canacquire(long *addr)
{
long value;
while((value=*addr) > 0)
if(cmpswap(addr, value, value-1))
return 1;
return 0;
}
/* Should we wake up? */
static int
semawoke(void *p)
{
coherence();
return !((Sema*)p)->waiting;
}
/* Acquire semaphore (subtract 1). */
static int
semacquire(Segment *s, long *addr, int block)
{
int acquired;
Sema phore;
if(canacquire(addr))
return 1;
if(!block)
return 0;
acquired = 0;
semqueue(s, addr, &phore);
for(;;){
phore.waiting = 1;
coherence();
if(canacquire(addr)){
acquired = 1;
break;
}
if(waserror())
break;
sleep(&phore, semawoke, &phore);
poperror();
}
semdequeue(s, &phore);
coherence(); /* not strictly necessary due to lock in semdequeue */
if(!phore.waiting)
semwakeup(s, addr, 1);
if(!acquired)
nexterror();
return 1;
}
/* Acquire semaphore or time-out */
static int
tsemacquire(Segment *s, long *addr, ulong ms)
{
int acquired, timedout;
ulong t, elms;
Sema phore;
if(canacquire(addr))
return 1;
if(ms == 0)
return 0;
acquired = timedout = 0;
semqueue(s, addr, &phore);
for(;;){
phore.waiting = 1;
coherence();
if(canacquire(addr)){
acquired = 1;
break;
}
if(waserror())
break;
t = m->ticks;
tsleep(&phore, semawoke, &phore, ms);
elms = TK2MS(m->ticks - t);
poperror();
if(elms >= ms){
timedout = 1;
break;
}
ms -= elms;
}
semdequeue(s, &phore);
coherence(); /* not strictly necessary due to lock in semdequeue */
if(!phore.waiting)
semwakeup(s, addr, 1);
if(timedout)
return 0;
if(!acquired)
nexterror();
return 1;
}
long
syssemacquire(ulong *arg)
{
int block;
long *addr;
Segment *s;
validaddr(arg[0], sizeof(long), 1);
evenaddr(arg[0]);
addr = (long*)arg[0];
block = arg[1];
if((s = seg(up, (ulong)addr, 0)) == nil)
error(Ebadarg);
if(*addr < 0)
error(Ebadarg);
return semacquire(s, addr, block);
}
long
systsemacquire(ulong *arg)
{
long *addr;
ulong ms;
Segment *s;
validaddr(arg[0], sizeof(long), 1);
evenaddr(arg[0]);
addr = (long*)arg[0];
ms = arg[1];
if((s = seg(up, (ulong)addr, 0)) == nil)
error(Ebadarg);
if(*addr < 0)
error(Ebadarg);
return tsemacquire(s, addr, ms);
}
long
syssemrelease(ulong *arg)
{
long *addr, delta;
Segment *s;
validaddr(arg[0], sizeof(long), 1);
evenaddr(arg[0]);
addr = (long*)arg[0];
delta = arg[1];
if((s = seg(up, (ulong)addr, 0)) == nil)
error(Ebadarg);
/* delta == 0 is a no-op, not a release */
if(delta < 0 || *addr < 0)
error(Ebadarg);
return semrelease(s, addr, delta);
}
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