xv6/proc.c
rtm 46bbd72f3e no more recursive locks
wakeup1() assumes you hold proc_table_lock
sleep(chan, lock) provides atomic sleep-and-release to wait for condition
ugly code in swtch/scheduler to implement new sleep
fix lots of bugs in pipes, wait, and exit
fix bugs if timer interrupt goes off in schedule()
console locks per line, not per byte
2006-07-15 12:03:57 +00:00

306 lines
6.6 KiB
C

#include "types.h"
#include "mmu.h"
#include "x86.h"
#include "param.h"
#include "fd.h"
#include "proc.h"
#include "defs.h"
#include "spinlock.h"
struct spinlock proc_table_lock;
struct proc proc[NPROC];
struct proc *curproc[NCPU];
int next_pid = 1;
/*
* set up a process's task state and segment descriptors
* correctly, given its current size and address in memory.
* this should be called whenever the latter change.
* doesn't change the cpu's current segmentation setup.
*/
void
setupsegs(struct proc *p)
{
memset(&p->ts, 0, sizeof(struct Taskstate));
p->ts.ts_ss0 = SEG_KDATA << 3;
p->ts.ts_esp0 = (unsigned)(p->kstack + KSTACKSIZE);
// XXX it may be wrong to modify the current segment table!
p->gdt[0] = SEG_NULL;
p->gdt[SEG_KCODE] = SEG(STA_X|STA_R, 0, 0xffffffff, 0);
p->gdt[SEG_KDATA] = SEG(STA_W, 0, 0xffffffff, 0);
p->gdt[SEG_TSS] = SEG16(STS_T32A, (unsigned) &p->ts,
sizeof(p->ts), 0);
p->gdt[SEG_TSS].sd_s = 0;
p->gdt[SEG_UCODE] = SEG(STA_X|STA_R, (unsigned)p->mem, p->sz, 3);
p->gdt[SEG_UDATA] = SEG(STA_W, (unsigned)p->mem, p->sz, 3);
p->gdt_pd.pd__garbage = 0;
p->gdt_pd.pd_lim = sizeof(p->gdt) - 1;
p->gdt_pd.pd_base = (unsigned) p->gdt;
}
extern void trapret();
/*
* internal fork(). does not copy kernel stack; instead,
* sets up the stack to return as if from system call.
* caller must set state to RUNNABLE.
*/
struct proc *
newproc()
{
struct proc *np;
struct proc *op;
int fd;
acquire(&proc_table_lock);
for(np = &proc[1]; np < &proc[NPROC]; np++){
if(np->state == UNUSED){
np->state = EMBRYO;
break;
}
}
if(np >= &proc[NPROC]){
release(&proc_table_lock);
return 0;
}
// copy from proc[0] if we're bootstrapping
op = curproc[cpu()];
if(op == 0)
op = &proc[0];
np->pid = next_pid++;
np->ppid = op->pid;
release(&proc_table_lock);
np->sz = op->sz;
np->mem = kalloc(op->sz);
if(np->mem == 0)
return 0;
memcpy(np->mem, op->mem, np->sz);
np->kstack = kalloc(KSTACKSIZE);
if(np->kstack == 0){
kfree(np->mem, op->sz);
np->state = UNUSED;
return 0;
}
setupsegs(np);
// set up kernel stack to return to user space
np->tf = (struct Trapframe *) (np->kstack + KSTACKSIZE - sizeof(struct Trapframe));
*(np->tf) = *(op->tf);
np->tf->tf_regs.reg_eax = 0; // so fork() returns 0 in child
// set up new jmpbuf to start executing at trapret with esp pointing at tf
memset(&np->jmpbuf, 0, sizeof np->jmpbuf);
np->jmpbuf.jb_eip = (unsigned) trapret;
np->jmpbuf.jb_esp = (unsigned) np->tf - 4; // -4 for the %eip that isn't actually there
// copy file descriptors
for(fd = 0; fd < NOFILE; fd++){
np->fds[fd] = op->fds[fd];
if(np->fds[fd])
fd_reference(np->fds[fd]);
}
return np;
}
void
scheduler(void)
{
struct proc *op, *np;
int i;
cprintf("start scheduler on cpu %d jmpbuf %p\n", cpu(), &cpus[cpu()].jmpbuf);
cpus[cpu()].lastproc = &proc[0];
setjmp(&cpus[cpu()].jmpbuf);
op = curproc[cpu()];
if(op == 0 || op->mtx != &proc_table_lock)
acquire1(&proc_table_lock, op);
if(op){
if(op->newstate <= 0 || op->newstate > ZOMBIE)
panic("scheduler");
op->state = op->newstate;
op->newstate = -1;
if(op->mtx){
struct spinlock *mtx = op->mtx;
op->mtx = 0;
if(mtx != &proc_table_lock)
release1(mtx, op);
}
}
// find a runnable process and switch to it
curproc[cpu()] = 0;
np = cpus[cpu()].lastproc + 1;
while(1){
for(i = 0; i < NPROC; i++){
if(np >= &proc[NPROC])
np = &proc[0];
if(np->state == RUNNABLE)
break;
np++;
}
if(i < NPROC){
np->state = RUNNING;
release1(&proc_table_lock, op);
break;
}
release1(&proc_table_lock, op);
op = 0;
acquire(&proc_table_lock);
np = &proc[0];
}
cpus[cpu()].lastproc = np;
curproc[cpu()] = np;
// h/w sets busy bit in TSS descriptor sometimes, and faults
// if it's set in LTR. so clear tss descriptor busy bit.
np->gdt[SEG_TSS].sd_type = STS_T32A;
// XXX should probably have an lgdt() function in x86.h
// to confine all the inline assembly.
// XXX probably ought to lgdt on trap return too, in case
// a system call has moved a program or changed its size.
asm volatile("lgdt %0" : : "g" (np->gdt_pd.pd_lim));
ltr(SEG_TSS << 3);
if(0) cprintf("cpu%d: run %d esp=%p callerpc=%p\n", cpu(), np-proc);
longjmp(&np->jmpbuf);
}
// give up the cpu by switching to the scheduler,
// which runs on the per-cpu stack.
void
swtch(int newstate)
{
struct proc *p = curproc[cpu()];
if(p == 0)
panic("swtch no proc");
if(p->mtx == 0 && p->locks != 0)
panic("swtch w/ locks");
if(p->mtx && p->locks != 1)
panic("swtch w/ locks 1");
if(p->mtx && p->mtx->locked == 0)
panic("switch w/ lock but not held");
if(p->locks && (read_eflags() & FL_IF))
panic("swtch w/ lock but FL_IF");
p->newstate = newstate; // basically an argument to scheduler()
if(setjmp(&p->jmpbuf) == 0)
longjmp(&cpus[cpu()].jmpbuf);
}
void
sleep(void *chan, struct spinlock *mtx)
{
struct proc *p = curproc[cpu()];
if(p == 0)
panic("sleep");
p->chan = chan;
p->mtx = mtx; // scheduler will release it
swtch(WAITING);
if(mtx)
acquire(mtx);
p->chan = 0;
}
void
wakeup1(void *chan)
{
struct proc *p;
for(p = proc; p < &proc[NPROC]; p++)
if(p->state == WAITING && p->chan == chan)
p->state = RUNNABLE;
}
void
wakeup(void *chan)
{
acquire(&proc_table_lock);
wakeup1(chan);
release(&proc_table_lock);
}
// give up the CPU but stay marked as RUNNABLE
void
yield()
{
if(curproc[cpu()] == 0 || curproc[cpu()]->state != RUNNING)
panic("yield");
swtch(RUNNABLE);
}
void
proc_exit()
{
struct proc *p;
struct proc *cp = curproc[cpu()];
int fd;
for(fd = 0; fd < NOFILE; fd++){
if(cp->fds[fd]){
fd_close(cp->fds[fd]);
cp->fds[fd] = 0;
}
}
acquire(&proc_table_lock);
// wake up parent
for(p = proc; p < &proc[NPROC]; p++)
if(p->pid == cp->ppid)
wakeup1(p);
// abandon children
for(p = proc; p < &proc[NPROC]; p++)
if(p->ppid == cp->pid)
p->pid = 1;
cp->mtx = &proc_table_lock;
swtch(ZOMBIE);
panic("a zombie revived");
}
// disable interrupts
void
cli(void)
{
if(cpus[cpu()].clis == 0)
__asm __volatile("cli");
cpus[cpu()].clis += 1;
if((read_eflags() & FL_IF) != 0)
panic("cli but enabled");
}
// enable interrupts
void
sti(void)
{
if((read_eflags() & FL_IF) != 0)
panic("sti but enabled");
if(cpus[cpu()].clis < 1)
panic("sti");
cpus[cpu()].clis -= 1;
if(cpus[cpu()].clis < 1)
__asm __volatile("sti");
}