sanchayanmaity/xv6-cs450
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no more recursive locks

Browse source 
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
This commit is contained in:
rtm 2006-07-15 12:03:57 +00:00
parent d9872ffa95
commit 46bbd72f3e
15 changed files with 231 additions and 104 deletions
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23
Notes
View file

@ -126,3 +126,26 @@ nasty hack to allow locks before first process,
race between release and sleep in sys_wait()
race between sys_exit waking up parent and setting state=ZOMBIE
race in pipe code when full/empty
lock order
per-pipe lock
proc_table_lock fd_table_lock kalloc_lock
console_lock
condition variable + mutex that protects it
proc * (for wait()), proc_table_lock
pipe structure, pipe lock
systematic way to test sleep races?
print something at the start of sleep?
do you have to be holding the mutex in order to call wakeup()?
should lock around printf, not putc
device interrupts don't clear FL_IF
so a recursive timer interrupt is possible
the sleep/swtch/schedule code that holds over a lock is ugly

39
console.c
View file

@ -4,7 +4,8 @@
#include "spinlock.h"
struct spinlock console_lock;
int use_printf_lock = 0;
int paniced = 0;
int use_console_lock = 0;
/*
* copy console output to parallel port, which you can tell
@ -23,15 +24,18 @@ lpt_putc(int c)
outb(0x378+2, 0x08);
}
void
cons_putc(int c)
static void
real_cons_putc(int c)
{
int crtport = 0x3d4; // io port of CGA
unsigned short *crt = (unsigned short *) 0xB8000; // base of CGA memory
int ind;
if(use_printf_lock)
acquire(&console_lock);
if(paniced){
cli();
while(1)
;
}
lpt_putc(c);
@ -63,8 +67,15 @@ cons_putc(int c)
outb(crtport + 1, ind >> 8);
outb(crtport, 15);
outb(crtport + 1, ind);
}
if(use_printf_lock)
void
cons_putc(int c)
{
if(use_console_lock)
acquire(&console_lock);
real_cons_putc(c);
if(use_console_lock)
release(&console_lock);
}
@ -91,7 +102,7 @@ printint(int xx, int base, int sgn)
while(i > 0){
i -= 1;
cons_putc(buf[i]);
real_cons_putc(buf[i]);
}
}
@ -104,13 +115,16 @@ cprintf(char *fmt, ...)
int i, state = 0, c;
unsigned int *ap = (unsigned int *) &fmt + 1;
if(use_console_lock)
acquire(&console_lock);
for(i = 0; fmt[i]; i++){
c = fmt[i] & 0xff;
if(state == 0){
if(c == '%'){
state = '%';
} else {
cons_putc(c);
real_cons_putc(c);
}
} else if(state == '%'){
if(c == 'd'){
@ -120,20 +134,25 @@ cprintf(char *fmt, ...)
printint(*ap, 16, 0);
ap++;
} else if(c == '%'){
cons_putc(c);
real_cons_putc(c);
}
state = 0;
}
}
if(use_console_lock)
release(&console_lock);
}
void
panic(char *s)
{
use_printf_lock = 0;
__asm __volatile("cli");
use_console_lock = 0;
cprintf("panic: ");
cprintf(s, 0);
cprintf("\n", 0);
paniced = 1; // freeze other CPU
while(1)
;
}

5
defs.h
View file

@ -14,7 +14,8 @@ struct jmpbuf;
void setupsegs(struct proc *);
struct proc * newproc(void);
void swtch(int);
void sleep(void *);
struct spinlock;
void sleep(void *, struct spinlock *);
void wakeup(void *);
void scheduler(void);
void proc_exit(void);
@ -65,6 +66,8 @@ int cpu(void);
struct spinlock;
void acquire(struct spinlock * lock);
void release(struct spinlock * lock);
void acquire1(struct spinlock * lock, struct proc *);
void release1(struct spinlock * lock, struct proc *);
// main.c
void load_icode(struct proc *p, uint8_t *binary, unsigned size);

2
ide.c
View file

@ -112,7 +112,7 @@ ide_start_read(uint32_t secno, void *dst, unsigned nsecs)
panic("ide_start_read: nsecs too large");
while ((head + 1) % NREQUEST == tail)
sleep (&disk_channel);
sleep (&disk_channel, 0);
r = &request[head];
r->secno = secno;

4
main.c
View file

@ -16,7 +16,7 @@ extern char _binary_user1_start[], _binary_user1_size[];
extern char _binary_usertests_start[], _binary_usertests_size[];
extern char _binary_userfs_start[], _binary_userfs_size[];
extern use_printf_lock;
extern int use_console_lock;
int
main()
@ -40,7 +40,7 @@ main()
mp_init(); // collect info about this machine
use_printf_lock = 1;
use_console_lock = 1;
cpus[cpu()].clis = 1; // cpu starts as if we had called cli()

19
pipe.c
View file

@ -81,16 +81,17 @@ pipe_write(struct pipe *p, char *addr, int n)
for(i = 0; i < n; i++){
while(((p->writep + 1) % PIPESIZE) == p->readp){
if(p->readopen == 0)
return -1;
if(p->readopen == 0){
release(&p->lock);
return -1;
}
wakeup(&p->readp);
sleep(&p->writep);
acquire(&p->lock);
sleep(&p->writep, &p->lock);
}
p->data[p->writep] = addr[i];
p->writep = (p->writep + 1) % PIPESIZE;
}
release(&p->lock);
wakeup(&p->readp);
return i;
@ -101,19 +102,23 @@ pipe_read(struct pipe *p, char *addr, int n)
{
int i;
acquire(&p->lock);
while(p->readp == p->writep){
if(p->writeopen == 0)
if(p->writeopen == 0){
release(&p->lock);
return 0;
sleep(&p->readp);
}
sleep(&p->readp, &p->lock);
}
acquire(&p->lock);
for(i = 0; i < n; i++){
if(p->readp == p->writep)
break;
addr[i] = p->data[p->readp];
p->readp = (p->readp + 1) % PIPESIZE;
}
release(&p->lock);
wakeup(&p->writep);
return i;

75
proc.c
View file

@ -95,7 +95,6 @@ newproc()
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
cprintf("newproc pid=%d return to %x:%x tf-%p\n", np->pid, np->tf->tf_cs, np->tf->tf_eip, np->tf);
// set up new jmpbuf to start executing at trapret with esp pointing at tf
memset(&np->jmpbuf, 0, sizeof np->jmpbuf);
@ -109,8 +108,6 @@ newproc()
fd_reference(np->fds[fd]);
}
cprintf("newproc %x\n", np);
return np;
}
@ -126,18 +123,27 @@ scheduler(void)
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){
acquire(&proc_table_lock);
for(i = 0; i < NPROC; i++){
if(np >= &proc[NPROC])
np = &proc[0];
@ -148,11 +154,13 @@ scheduler(void)
if(i < NPROC){
np->state = RUNNING;
release(&proc_table_lock);
release1(&proc_table_lock, op);
break;
}
release(&proc_table_lock);
release1(&proc_table_lock, op);
op = 0;
acquire(&proc_table_lock);
np = &proc[0];
}
@ -180,36 +188,56 @@ void
swtch(int newstate)
{
struct proc *p = curproc[cpu()];
if(p == 0)
panic("swtch no proc");
if(p->locks != 0)
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)
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)
{
struct proc *p;
acquire(&proc_table_lock);
for(p = proc; p < &proc[NPROC]; p++){
if(p->state == WAITING && p->chan == chan){
p->state = RUNNABLE;
}
}
wakeup1(chan);
release(&proc_table_lock);
}
@ -229,8 +257,6 @@ proc_exit()
struct proc *cp = curproc[cpu()];
int fd;
cprintf("exit %x pid %d ppid %d\n", cp, cp->pid, cp->ppid);
for(fd = 0; fd < NOFILE; fd++){
if(cp->fds[fd]){
fd_close(cp->fds[fd]);
@ -243,32 +269,35 @@ proc_exit()
// wake up parent
for(p = proc; p < &proc[NPROC]; p++)
if(p->pid == cp->ppid)
wakeup(p);
wakeup1(p);
// abandon children
for(p = proc; p < &proc[NPROC]; p++)
if(p->ppid == cp->pid)
p->pid = 1;
release(&proc_table_lock);
// switch into scheduler
cp->mtx = &proc_table_lock;
swtch(ZOMBIE);
panic("a zombie revived");
}
// disable interrupts
void
cli(void)
{
cpus[cpu()].clis += 1;
if(cpus[cpu()].clis == 1)
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;

1
proc.h
View file

@ -41,6 +41,7 @@ struct proc{
char *kstack; // kernel stack, separate from mem so it doesn't move
enum proc_state state;
enum proc_state newstate; // desired state after swtch()
struct spinlock *mtx; // mutex for condition variable
int pid;
int ppid;
void *chan; // sleep

46
spinlock.c
View file

@ -8,36 +8,20 @@
#define DEBUG 0
extern use_printf_lock;
extern int use_console_lock;
int getcallerpc(void *v) {
return ((int*)v)[-1];
}
void
acquire(struct spinlock * lock)
acquire1(struct spinlock * lock, struct proc *cp)
{
struct proc *cp = curproc[cpu()];
unsigned who;
if(cp)
who = (unsigned) cp;
else
who = cpu() + 1;
if(DEBUG) cprintf("cpu%d: acquiring at %x\n", cpu(), getcallerpc(&lock));
if (lock->who == who && lock->locked){
lock->count += 1;
} else {
cli();
// if we get the lock, eax will be zero
// if we don't get the lock, eax will be one
while ( cmpxchg(0, 1, &lock->locked) == 1 ) { ; }
lock->locker_pc = getcallerpc(&lock);
lock->count = 1;
lock->who = who;
}
if(cp)
cp->locks += 1;
@ -46,27 +30,29 @@ acquire(struct spinlock * lock)
}
void
release(struct spinlock * lock)
release1(struct spinlock * lock, struct proc *cp)
{
struct proc *cp = curproc[cpu()];
unsigned who;
if(cp)
who = (unsigned) cp;
else
who = cpu() + 1;
if(DEBUG) cprintf ("cpu%d: releasing at %x\n", cpu(), getcallerpc(&lock));
if(lock->who != who || lock->count < 1 || lock->locked != 1)
if(lock->locked != 1)
panic("release");
lock->count -= 1;
if(cp)
cp->locks -= 1;
if(lock->count < 1){
lock->who = 0;
cmpxchg(1, 0, &lock->locked);
sti();
}
void
acquire(struct spinlock *lock)
{
acquire1(lock, curproc[cpu()]);
}
void
release(struct spinlock *lock)
{
release1(lock, curproc[cpu()]);
}

2
spinlock.h
View file

@ -1,6 +1,4 @@
struct spinlock {
unsigned int locked;
unsigned who;
int count;
unsigned locker_pc;
};

29
syscall.c
View file

@ -152,8 +152,12 @@ sys_fork()
struct proc *np;
np = newproc();
if(np){
np->state = RUNNABLE;
return np->pid;
} else {
return -1;
}
}
int
@ -170,11 +174,10 @@ sys_wait()
struct proc *cp = curproc[cpu()];
int any, pid;
cprintf("waid pid %d ppid %d\n", cp->pid, cp->ppid);
acquire(&proc_table_lock);
while(1){
any = 0;
acquire(&proc_table_lock);
for(p = proc; p < &proc[NPROC]; p++){
if(p->state == ZOMBIE && p->ppid == cp->pid){
kfree(p->mem, p->sz);
@ -182,18 +185,16 @@ sys_wait()
pid = p->pid;
p->state = UNUSED;
release(&proc_table_lock);
cprintf("%x collected %x\n", cp, p);
return pid;
}
if(p->state != UNUSED && p->ppid == cp->pid)
any = 1;
}
release(&proc_table_lock);
if(any == 0){
cprintf("%x nothing to wait for\n", cp);
release(&proc_table_lock);
return -1;
}
sleep(cp);
sleep(cp, &proc_table_lock);
}
}
@ -220,7 +221,7 @@ sys_block(void)
panic("couldn't start read\n");
}
cprintf("call sleep\n");
sleep (c);
sleep (c, 0);
if (ide_finish_read(c)) {
panic("couldn't do read\n");
}
@ -253,6 +254,17 @@ sys_kill()
return -1;
}
int
sys_panic()
{
struct proc *p = curproc[cpu()];
unsigned int addr;
fetcharg(0, &addr);
panic(p->mem + addr);
return 0;
}
void
syscall()
{
@ -292,6 +304,9 @@ syscall()
case SYS_kill:
ret = sys_kill();
break;
case SYS_panic:
ret = sys_panic();
break;
default:
cprintf("unknown sys call %d\n", num);
// XXX fault

1
syscall.h
View file

@ -8,3 +8,4 @@
#define SYS_close 8
#define SYS_block 9
#define SYS_kill 10
#define SYS_panic 11

24
trap.c
View file

@ -36,8 +36,14 @@ trap(struct Trapframe *tf)
{
int v = tf->tf_trapno;
if(cpus[cpu()].clis){
cprintf("cpu %d v %d eip %x\n", cpu(), v, tf->tf_eip);
panic("interrupt while interrupts are off");
}
if(v == T_SYSCALL){
struct proc *cp = curproc[cpu()];
int num = cp->tf->tf_regs.reg_eax;
if(cp == 0)
panic("syscall with no proc");
if(cp->killed)
@ -50,6 +56,14 @@ trap(struct Trapframe *tf)
panic("trap ret but not RUNNING");
if(tf != cp->tf)
panic("trap ret wrong tf");
if(cp->locks){
cprintf("num=%d\n", num);
panic("syscall returning locks held");
}
if(cpus[cpu()].clis)
panic("syscall returning but clis != 0");
if((read_eflags() & FL_IF) == 0)
panic("syscall returning but FL_IF clear");
if(read_esp() < (unsigned)cp->kstack ||
read_esp() >= (unsigned)cp->kstack + KSTACKSIZE)
panic("trap ret esp wrong");
@ -61,13 +75,19 @@ trap(struct Trapframe *tf)
if(v == (IRQ_OFFSET + IRQ_TIMER)){
struct proc *cp = curproc[cpu()];
lapic_timerintr();
if(cp && cp->locks)
panic("timer interrupt while holding a lock");
if(cp){
if(cpus[cpu()].clis != 0)
panic("trap clis > 0");
#if 1
if((read_eflags() & FL_IF) == 0)
panic("timer interrupt but interrupts now disabled");
#else
cpus[cpu()].clis += 1;
sti();
#endif
if(cp->killed)
proc_exit();
if(cp->state == RUNNING)
yield();
}
return;

44
usertests.c
View file

@ -16,7 +16,7 @@ pipe1()
for(i = 0; i < 1033; i++)
buf[i] = seq++;
if(write(fds[1], buf, 1033) != 1033){
puts("pipe1 oops 1\n");
panic("pipe1 oops 1\n");
exit(1);
}
}
@ -31,7 +31,7 @@ pipe1()
break;
for(i = 0; i < n; i++){
if((buf[i] & 0xff) != (seq++ & 0xff)){
puts("pipe1 oops 2\n");
panic("pipe1 oops 2\n");
return;
}
}
@ -41,8 +41,9 @@ pipe1()
cc = sizeof(buf);
}
if(total != 5 * 1033)
puts("pipe1 oops 3\n");
panic("pipe1 oops 3\n");
close(fds[0]);
wait();
}
puts("pipe1 ok\n");
}
@ -69,7 +70,7 @@ preempt()
if(pid3 == 0){
close(pfds[0]);
if(write(pfds[1], "x", 1) != 1)
puts("preempt write error");
panic("preempt write error");
close(pfds[1]);
while(1)
;
@ -77,7 +78,7 @@ preempt()
close(pfds[1]);
if(read(pfds[0], buf, sizeof(buf)) != 1){
puts("preempt read error");
panic("preempt read error");
return;
}
close(pfds[0]);
@ -90,12 +91,37 @@ preempt()
puts("preempt ok\n");
}
// try to find any races between exit and wait
void
exitwait()
{
int i, pid;
for(i = 0; i < 100; i++){
pid = fork();
if(pid < 0){
panic("fork failed\n");
return;
}
if(pid){
if(wait() != pid){
panic("wait wrong pid\n");
return;
}
} else {
exit(0);
}
}
puts("exitwait ok\n");
}
main()
{
puts("usertests starting\n");
pipe1();
//preempt();
while(1)
;
pipe1();
preempt();
exitwait();
panic("usertests finished successfuly");
}

1
usys.S
View file

@ -18,3 +18,4 @@ STUB(write)
STUB(close)
STUB(block)
STUB(kill)
STUB(panic)