diff options
Diffstat (limited to 'spinlock.c')
| -rw-r--r-- | spinlock.c | 19 |
1 files changed, 10 insertions, 9 deletions
@@ -10,12 +10,6 @@ extern int use_console_lock; -// Barrier to gcc's instruction reordering. -static void inline gccbarrier(void) -{ - asm volatile("" : : : "memory"); -} - void initlock(struct spinlock *lock, char *name) { @@ -35,7 +29,10 @@ acquire(struct spinlock *lock) if(holding(lock)) panic("acquire"); - while(cmpxchg(0, 1, &lock->locked) == 1) + // The xchg is atomic. + // It also serializes, so that reads after acquire are not + // reordered before it. + while(xchg(&lock->locked, 1) == 1) ; // Record info about lock acquisition for debugging. @@ -56,8 +53,12 @@ release(struct spinlock *lock) lock->pcs[0] = 0; lock->cpu = 0xffffffff; - gccbarrier(); // Keep gcc from moving lock->locked = 0 earlier. - lock->locked = 0; + // The xchg serializes, so that reads before release are + // not reordered after it. (This reordering would be allowed + // by the Intel manuals, but does not happen on current + // Intel processors. The xchg being asm volatile also keeps + // gcc from delaying the above assignments.) + xchg(&lock->locked, 0); popcli(); } |