1*31085bb4Srsc // Mutual exclusion spin locks. 2*31085bb4Srsc 321a88fd4Skaashoek #include "types.h" 421a88fd4Skaashoek #include "defs.h" 521a88fd4Skaashoek #include "x86.h" 67837c71bSkaashoek #include "mmu.h" 74e8f237bSrtm #include "param.h" 84e8f237bSrtm #include "proc.h" 94e8f237bSrtm #include "spinlock.h" 1021a88fd4Skaashoek 11b74f4b57Srsc extern int use_console_lock; 128148b6eeSrtm 130e84a0ecSrtm void 145be0039cSrtm initlock(struct spinlock *lock, char *name) 155be0039cSrtm { 165be0039cSrtm lock->name = name; 175be0039cSrtm lock->locked = 0; 185be0039cSrtm lock->cpu = 0xffffffff; 195be0039cSrtm } 205be0039cSrtm 21*31085bb4Srsc // Record the current call stack in pcs[] by following the %ebp chain. 225be0039cSrtm void 230e84a0ecSrtm getcallerpcs(void *v, uint pcs[]) 2465bd8e13Srsc { 250e84a0ecSrtm uint *ebp = (uint*)v - 2; 260e84a0ecSrtm int i; 270cfc7290Srsc for(i = 0; i < 10; i++){ 280cfc7290Srsc if(ebp == 0 || ebp == (uint*)0xffffffff) 290cfc7290Srsc break; 300cfc7290Srsc pcs[i] = ebp[1]; // saved %eip 310cfc7290Srsc ebp = (uint*)ebp[0]; // saved %ebp 320e84a0ecSrtm } 330e84a0ecSrtm for(; i < 10; i++) 340e84a0ecSrtm pcs[i] = 0; 355ce9751cSrsc } 365ce9751cSrsc 37*31085bb4Srsc // Acquire the lock. 38*31085bb4Srsc // Loops (spins) until the lock is acquired. 39*31085bb4Srsc // (Because contention is handled by spinning, must not 40*31085bb4Srsc // go to sleep holding any locks.) 4121a88fd4Skaashoek void 42679a977cSrsc acquire(struct spinlock *lock) 4321a88fd4Skaashoek { 440e84a0ecSrtm if(holding(lock)) 450dd42537Srsc panic("acquire"); 460dd42537Srsc 478a8be1b8Srtm if(cpus[cpu()].nlock == 0) 48b548df15Srtm cli(); 498a8be1b8Srtm cpus[cpu()].nlock++; 508a8be1b8Srtm 5165bd8e13Srsc while(cmpxchg(0, 1, &lock->locked) == 1) 5265bd8e13Srsc ; 5365bd8e13Srsc cpuid(0, 0, 0, 0, 0); // memory barrier 54*31085bb4Srsc 55*31085bb4Srsc // Record info about lock acquisition for debugging. 56*31085bb4Srsc // The +10 is only so that we can tell the difference 57*31085bb4Srsc // between forgetting to initialize lock->cpu 58*31085bb4Srsc // and holding a lock on cpu 0. 590e84a0ecSrtm lock->cpu = cpu() + 10; 60*31085bb4Srsc getcallerpcs(&lock, lock->pcs); 6121a88fd4Skaashoek } 6221a88fd4Skaashoek 63*31085bb4Srsc // Release the lock. 6421a88fd4Skaashoek void 65679a977cSrsc release(struct spinlock *lock) 6621a88fd4Skaashoek { 675be0039cSrtm 680dd42537Srsc if(!holding(lock)) 690dd42537Srsc panic("release"); 700dd42537Srsc 710e84a0ecSrtm lock->pcs[0] = 0; 720e84a0ecSrtm lock->cpu = 0xffffffff; 7365bd8e13Srsc cpuid(0, 0, 0, 0, 0); // memory barrier 7465bd8e13Srsc lock->locked = 0; 75b74f4b57Srsc if(--cpus[cpu()].nlock == 0) 76b548df15Srtm sti(); 7721a88fd4Skaashoek } 7846bbd72fSrtm 79*31085bb4Srsc // Check whether this cpu is holding the lock. 800dd42537Srsc int 810dd42537Srsc holding(struct spinlock *lock) 820dd42537Srsc { 830e84a0ecSrtm return lock->locked && lock->cpu == cpu() + 10; 840dd42537Srsc } 85