90 lines
2 KiB
C
90 lines
2 KiB
C
// Mutual exclusion spin locks.
|
|
|
|
#include "types.h"
|
|
#include "defs.h"
|
|
#include "x86.h"
|
|
#include "mmu.h"
|
|
#include "param.h"
|
|
#include "proc.h"
|
|
#include "spinlock.h"
|
|
|
|
extern int use_console_lock;
|
|
|
|
void
|
|
initlock(struct spinlock *lock, char *name)
|
|
{
|
|
lock->name = name;
|
|
lock->locked = 0;
|
|
lock->cpu = 0xffffffff;
|
|
}
|
|
|
|
// Record the current call stack in pcs[] by following the %ebp chain.
|
|
void
|
|
getcallerpcs(void *v, uint pcs[])
|
|
{
|
|
uint *ebp = (uint*)v - 2;
|
|
int i;
|
|
for(i = 0; i < 10; i++){
|
|
if(ebp == 0 || ebp == (uint*)0xffffffff)
|
|
break;
|
|
pcs[i] = ebp[1]; // saved %eip
|
|
ebp = (uint*)ebp[0]; // saved %ebp
|
|
}
|
|
for(; i < 10; i++)
|
|
pcs[i] = 0;
|
|
}
|
|
|
|
// Acquire the lock.
|
|
// Loops (spins) until the lock is acquired.
|
|
// (Because contention is handled by spinning, must not
|
|
// go to sleep holding any locks.)
|
|
void
|
|
acquire(struct spinlock *lock)
|
|
{
|
|
if(holding(lock))
|
|
panic("acquire");
|
|
|
|
if(cpus[cpu()].nlock == 0)
|
|
cli();
|
|
cpus[cpu()].nlock++;
|
|
|
|
while(cmpxchg(0, 1, &lock->locked) == 1)
|
|
;
|
|
|
|
// Serialize instructions: now that lock is acquired, make sure
|
|
// we wait for all pending writes from other processors.
|
|
cpuid(0, 0, 0, 0, 0); // memory barrier (see Ch 7 of IA-32 manual, vol 3)
|
|
|
|
// Record info about lock acquisition for debugging.
|
|
// The +10 is only so that we can tell the difference
|
|
// between forgetting to initialize lock->cpu
|
|
// and holding a lock on cpu 0.
|
|
lock->cpu = cpu() + 10;
|
|
getcallerpcs(&lock, lock->pcs);
|
|
}
|
|
|
|
// Release the lock.
|
|
void
|
|
release(struct spinlock *lock)
|
|
{
|
|
if(!holding(lock))
|
|
panic("release");
|
|
|
|
lock->pcs[0] = 0;
|
|
lock->cpu = 0xffffffff;
|
|
|
|
// Serialize instructions: before unlocking the lock, make sure
|
|
// to flush any pending memory writes from this processor.
|
|
cpuid(0, 0, 0, 0, 0); // memory barrier (see Ch 7 of IA-32 manual, vol 3)
|
|
|
|
lock->locked = 0;
|
|
if(--cpus[cpu()].nlock == 0)
|
|
sti();
|
|
}
|
|
|
|
// Check whether this cpu is holding the lock.
|
|
int
|
|
holding(struct spinlock *lock)
|
|
{
|
|
return lock->locked && lock->cpu == cpu() + 10;
|
|
}
|