xv6/proc.c
rsc ab08960f64 Final word on the locking fiasco?
Change pushcli / popcli so that they can never turn on
interrupts unexpectedly.  That is, if interrupts are on,
then pushcli(); popcli(); turns them off and back on, but
if they are off to begin with, then pushcli(); popcli(); is
a no-op.

I think our fundamental mistake was having a primitive
(release and then popcli nee spllo) that could turn
interrupts on at unexpected moments instead of being
explicit about when we want to start allowing interrupts.

With the new semantics, all the manual fiddling of ncli
to force interrupts off in certain sections goes away.
In return, we must explicitly mark the places where
we want to enable interrupts unconditionally, by calling sti().
There is only one: inside the scheduler loop.
2007-09-27 21:25:37 +00:00

484 lines
10 KiB
C

#include "types.h"
#include "defs.h"
#include "param.h"
#include "mmu.h"
#include "x86.h"
#include "proc.h"
#include "spinlock.h"
struct spinlock proc_table_lock;
struct proc proc[NPROC];
static struct proc *initproc;
int nextpid = 1;
extern void forkret(void);
extern void forkret1(struct trapframe*);
void
pinit(void)
{
initlock(&proc_table_lock, "proc_table");
}
// Look in the process table for an UNUSED proc.
// If found, change state to EMBRYO and return it.
// Otherwise return 0.
static struct proc*
allocproc(void)
{
int i;
struct proc *p;
acquire(&proc_table_lock);
for(i = 0; i < NPROC; i++){
p = &proc[i];
if(p->state == UNUSED){
p->state = EMBRYO;
p->pid = nextpid++;
release(&proc_table_lock);
return p;
}
}
release(&proc_table_lock);
return 0;
}
// Grow current process's memory by n bytes.
// Return old size on success, -1 on failure.
int
growproc(int n)
{
char *newmem, *oldmem;
newmem = kalloc(cp->sz + n);
if(newmem == 0)
return -1;
memmove(newmem, cp->mem, cp->sz);
memset(newmem + cp->sz, 0, n);
oldmem = cp->mem;
cp->mem = newmem;
kfree(oldmem, cp->sz);
cp->sz += n;
setupsegs(cp);
return cp->sz - n;
}
// Set up CPU's segment descriptors and task state for a given process.
// If p==0, set up for "idle" state for when scheduler() is running.
void
setupsegs(struct proc *p)
{
struct cpu *c;
pushcli();
c = &cpus[cpu()];
c->ts.ss0 = SEG_KDATA << 3;
if(p)
c->ts.esp0 = (uint)(p->kstack + KSTACKSIZE);
else
c->ts.esp0 = 0xffffffff;
c->gdt[0] = SEG_NULL;
c->gdt[SEG_KCODE] = SEG(STA_X|STA_R, 0, 0x100000 + 64*1024-1, 0);
c->gdt[SEG_KDATA] = SEG(STA_W, 0, 0xffffffff, 0);
c->gdt[SEG_TSS] = SEG16(STS_T32A, (uint)&c->ts, sizeof(c->ts)-1, 0);
c->gdt[SEG_TSS].s = 0;
if(p){
c->gdt[SEG_UCODE] = SEG(STA_X|STA_R, (uint)p->mem, p->sz-1, DPL_USER);
c->gdt[SEG_UDATA] = SEG(STA_W, (uint)p->mem, p->sz-1, DPL_USER);
} else {
c->gdt[SEG_UCODE] = SEG_NULL;
c->gdt[SEG_UDATA] = SEG_NULL;
}
lgdt(c->gdt, sizeof(c->gdt));
ltr(SEG_TSS << 3);
popcli();
}
// Create a new process copying p as the parent.
// Sets up stack to return as if from system call.
// Caller must set state of returned proc to RUNNABLE.
struct proc*
copyproc(struct proc *p)
{
int i;
struct proc *np;
// Allocate process.
if((np = allocproc()) == 0)
return 0;
// Allocate kernel stack.
if((np->kstack = kalloc(KSTACKSIZE)) == 0){
np->state = UNUSED;
return 0;
}
np->tf = (struct trapframe*)(np->kstack + KSTACKSIZE) - 1;
if(p){ // Copy process state from p.
np->parent = p;
memmove(np->tf, p->tf, sizeof(*np->tf));
np->sz = p->sz;
if((np->mem = kalloc(np->sz)) == 0){
kfree(np->kstack, KSTACKSIZE);
np->kstack = 0;
np->state = UNUSED;
return 0;
}
memmove(np->mem, p->mem, np->sz);
for(i = 0; i < NOFILE; i++)
if(p->ofile[i])
np->ofile[i] = filedup(p->ofile[i]);
np->cwd = idup(p->cwd);
}
// Set up new context to start executing at forkret (see below).
memset(&np->context, 0, sizeof(np->context));
np->context.eip = (uint)forkret;
np->context.esp = (uint)np->tf;
// Clear %eax so that fork system call returns 0 in child.
np->tf->eax = 0;
return np;
}
// Set up first user process.
void
userinit(void)
{
struct proc *p;
extern uchar _binary_initcode_start[], _binary_initcode_size[];
p = copyproc(0);
p->sz = PAGE;
p->mem = kalloc(p->sz);
p->cwd = namei("/");
memset(p->tf, 0, sizeof(*p->tf));
p->tf->cs = (SEG_UCODE << 3) | DPL_USER;
p->tf->ds = (SEG_UDATA << 3) | DPL_USER;
p->tf->es = p->tf->ds;
p->tf->ss = p->tf->ds;
p->tf->eflags = FL_IF;
p->tf->esp = p->sz;
// Make return address readable; needed for some gcc.
p->tf->esp -= 4;
*(uint*)(p->mem + p->tf->esp) = 0xefefefef;
// On entry to user space, start executing at beginning of initcode.S.
p->tf->eip = 0;
memmove(p->mem, _binary_initcode_start, (int)_binary_initcode_size);
safestrcpy(p->name, "initcode", sizeof(p->name));
p->state = RUNNABLE;
initproc = p;
}
// Return currently running process.
struct proc*
curproc(void)
{
struct proc *p;
pushcli();
p = cpus[cpu()].curproc;
popcli();
return p;
}
//PAGEBREAK: 42
// Per-CPU process scheduler.
// Each CPU calls scheduler() after setting itself up.
// Scheduler never returns. It loops, doing:
// - choose a process to run
// - swtch to start running that process
// - eventually that process transfers control
// via swtch back to the scheduler.
void
scheduler(void)
{
struct proc *p;
struct cpu *c;
int i;
c = &cpus[cpu()];
for(;;){
// Enable interrupts on this processor.
sti();
// Loop over process table looking for process to run.
acquire(&proc_table_lock);
for(i = 0; i < NPROC; i++){
p = &proc[i];
if(p->state != RUNNABLE)
continue;
// Switch to chosen process. It is the process's job
// to release proc_table_lock and then reacquire it
// before jumping back to us.
c->curproc = p;
setupsegs(p);
p->state = RUNNING;
swtch(&c->context, &p->context);
// Process is done running for now.
// It should have changed its p->state before coming back.
c->curproc = 0;
setupsegs(0);
}
release(&proc_table_lock);
}
}
// Enter scheduler. Must already hold proc_table_lock
// and have changed curproc[cpu()]->state.
void
sched(void)
{
if(read_eflags()&FL_IF)
panic("sched interruptible");
if(cp->state == RUNNING)
panic("sched running");
if(!holding(&proc_table_lock))
panic("sched proc_table_lock");
if(cpus[cpu()].ncli != 1)
panic("sched locks");
swtch(&cp->context, &cpus[cpu()].context);
}
// Give up the CPU for one scheduling round.
void
yield(void)
{
acquire(&proc_table_lock);
cp->state = RUNNABLE;
sched();
release(&proc_table_lock);
}
// A fork child's very first scheduling by scheduler()
// will swtch here. "Return" to user space.
void
forkret(void)
{
// Still holding proc_table_lock from scheduler.
release(&proc_table_lock);
// Jump into assembly, never to return.
forkret1(cp->tf);
}
// Atomically release lock and sleep on chan.
// Reacquires lock when reawakened.
void
sleep(void *chan, struct spinlock *lk)
{
if(cp == 0)
panic("sleep");
if(lk == 0)
panic("sleep without lk");
// Must acquire proc_table_lock in order to
// change p->state and then call sched.
// Once we hold proc_table_lock, we can be
// guaranteed that we won't miss any wakeup
// (wakeup runs with proc_table_lock locked),
// so it's okay to release lk.
if(lk != &proc_table_lock){
acquire(&proc_table_lock);
release(lk);
}
// Go to sleep.
cp->chan = chan;
cp->state = SLEEPING;
sched();
// Tidy up.
cp->chan = 0;
// Reacquire original lock.
if(lk != &proc_table_lock){
release(&proc_table_lock);
acquire(lk);
}
}
//PAGEBREAK!
// Wake up all processes sleeping on chan.
// Proc_table_lock must be held.
static void
wakeup1(void *chan)
{
struct proc *p;
for(p = proc; p < &proc[NPROC]; p++)
if(p->state == SLEEPING && p->chan == chan)
p->state = RUNNABLE;
}
// Wake up all processes sleeping on chan.
// Proc_table_lock is acquired and released.
void
wakeup(void *chan)
{
acquire(&proc_table_lock);
wakeup1(chan);
release(&proc_table_lock);
}
// Kill the process with the given pid.
// Process won't actually exit until it returns
// to user space (see trap in trap.c).
int
kill(int pid)
{
struct proc *p;
acquire(&proc_table_lock);
for(p = proc; p < &proc[NPROC]; p++){
if(p->pid == pid){
p->killed = 1;
// Wake process from sleep if necessary.
if(p->state == SLEEPING)
p->state = RUNNABLE;
release(&proc_table_lock);
return 0;
}
}
release(&proc_table_lock);
return -1;
}
// Exit the current process. Does not return.
// Exited processes remain in the zombie state
// until their parent calls wait() to find out they exited.
void
exit(void)
{
struct proc *p;
int fd;
if(cp == initproc)
panic("init exiting");
// Close all open files.
for(fd = 0; fd < NOFILE; fd++){
if(cp->ofile[fd]){
fileclose(cp->ofile[fd]);
cp->ofile[fd] = 0;
}
}
iput(cp->cwd);
cp->cwd = 0;
acquire(&proc_table_lock);
// Parent might be sleeping in proc_wait.
wakeup1(cp->parent);
// Pass abandoned children to init.
for(p = proc; p < &proc[NPROC]; p++){
if(p->parent == cp){
p->parent = initproc;
if(p->state == ZOMBIE)
wakeup1(initproc);
}
}
// Jump into the scheduler, never to return.
cp->killed = 0;
cp->state = ZOMBIE;
sched();
panic("zombie exit");
}
// Wait for a child process to exit and return its pid.
// Return -1 if this process has no children.
int
wait(void)
{
struct proc *p;
int i, havekids, pid;
acquire(&proc_table_lock);
for(;;){
// Scan through table looking for zombie children.
havekids = 0;
for(i = 0; i < NPROC; i++){
p = &proc[i];
if(p->state == UNUSED)
continue;
if(p->parent == cp){
if(p->state == ZOMBIE){
// Found one.
kfree(p->mem, p->sz);
kfree(p->kstack, KSTACKSIZE);
pid = p->pid;
p->state = UNUSED;
p->pid = 0;
p->parent = 0;
p->name[0] = 0;
release(&proc_table_lock);
return pid;
}
havekids = 1;
}
}
// No point waiting if we don't have any children.
if(!havekids || cp->killed){
release(&proc_table_lock);
return -1;
}
// Wait for children to exit. (See wakeup1 call in proc_exit.)
sleep(cp, &proc_table_lock);
}
}
// Print a process listing to console. For debugging.
// Runs when user types ^P on console.
// No lock to avoid wedging a stuck machine further.
void
procdump(void)
{
static char *states[] = {
[UNUSED] "unused",
[EMBRYO] "embryo",
[SLEEPING] "sleep ",
[RUNNABLE] "runble",
[RUNNING] "run ",
[ZOMBIE] "zombie"
};
int i, j;
struct proc *p;
char *state;
uint pc[10];
for(i = 0; i < NPROC; i++){
p = &proc[i];
if(p->state == UNUSED)
continue;
if(p->state >= 0 && p->state < NELEM(states) && states[p->state])
state = states[p->state];
else
state = "???";
cprintf("%d %s %s", p->pid, state, p->name);
if(p->state == SLEEPING){
getcallerpcs((uint*)p->context.ebp+2, pc);
for(j=0; j<10 && pc[j] != 0; j++)
cprintf(" %p", pc[j]);
}
cprintf("\n");
}
}