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