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// Mutual exclusion spin locks.
#include "types.h"
#include "param.h"
#include "memlayout.h"
#include "spinlock.h"
#include "riscv.h"
#include "defs.h"
void
initlock(struct spinlock *lk, char *name)
{
lk->name = name;
lk->locked = 0;
lk->cpu = 0;
}
void
acquire(struct spinlock *lk)
{
lk->locked = 1;
lk->cpu = mycpu();
}
void
release(struct spinlock *lk)
{
lk->locked = 0;
lk->cpu = 0;
}
int
holding(struct spinlock *lk)
{
return lk->locked && lk->cpu == mycpu();
}
#if 0
// Acquire the lock.
// Loops (spins) until the lock is acquired.
// Holding a lock for a long time may cause
// other CPUs to waste time spinning to acquire it.
void
acquire(struct spinlock *lk)
{
pushcli(); // disable interrupts to avoid deadlock.
if(holding(lk))
panic("acquire");
// The xchg is atomic.
while(xchg(&lk->locked, 1) != 0)
;
// Tell the C compiler and the processor to not move loads or stores
// past this point, to ensure that the critical section's memory
// references happen after the lock is acquired.
__sync_synchronize();
// Record info about lock acquisition for holding() and debugging.
lk->cpu = mycpu();
getcallerpcs(&lk, lk->pcs);
}
// Release the lock.
void
release(struct spinlock *lk)
{
if(!holding(lk))
panic("release");
lk->pcs[0] = 0;
lk->cpu = 0;
// Tell the C compiler and the processor to not move loads or stores
// past this point, to ensure that all the stores in the critical
// section are visible to other cores before the lock is released.
// Both the C compiler and the hardware may re-order loads and
// stores; __sync_synchronize() tells them both not to.
__sync_synchronize();
// Release the lock, equivalent to lk->locked = 0.
// This code can't use a C assignment, since it might
// not be atomic. A real OS would use C atomics here.
asm volatile("movl $0, %0" : "+m" (lk->locked) : );
popcli();
}
// Record the current call stack in pcs[] by following the %ebp chain.
void
getcallerpcs(void *v, uint64 pcs[])
{
uint64 *ebp;
int i;
asm volatile("mov %%rbp, %0" : "=r" (ebp));
for(i = 0; i < 10; i++){
if(ebp == 0 || ebp < (uint64*)KERNBASE || ebp == (uint64*)0xffffffff)
break;
pcs[i] = ebp[1]; // saved %eip
ebp = (uint64*)ebp[0]; // saved %ebp
}
for(; i < 10; i++)
pcs[i] = 0;
}
// Check whether this cpu is holding the lock.
int
holding(struct spinlock *lk)
{
int r;
pushcli();
r = lk->locked && lk->cpu == mycpu();
popcli();
return r;
}
// Pushcli/popcli are like cli/sti except that they are matched:
// it takes two popcli to undo two pushcli. Also, if interrupts
// are off, then pushcli, popcli leaves them off.
void
pushcli(void)
{
int eflags;
eflags = readeflags();
cli();
if(mycpu()->ncli == 0)
mycpu()->intena = eflags & FL_IF;
mycpu()->ncli += 1;
}
void
popcli(void)
{
if(readeflags()&FL_IF)
panic("popcli - interruptible");
if(--mycpu()->ncli < 0)
panic("popcli");
if(mycpu()->ncli == 0 && mycpu()->intena)
sti();
}
#endif
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