Hi, For the following function, I have two questions: static inline int test_and_set_bit(int nr, volatile unsigned long * addr) { int oldbit; __asm__ __volatile__( LOCK_PREFIX "btsl %2,%1\n\tsbbl %0,%0" :"=r" (oldbit),"+m" (ADDR) :"Ir" (nr) : "memory"); return oldbit; } 1. There are two instructions in the inline assemably, namely btsl and sbbl. But, can the only one LOCK_PREFIX ensure that the operation is atomic? 2. The clobber list of the inline assembly contains a string of "memory". What is the meaning of this declaration and why does the operation need it ? After all, some other operations such as clear_bit() dose not need "memory" indeed. The declaration of "memory" appears in source code of kernel here and there, and bothers me for a long time. So any details about it will be appreciated. static inline void clear_bit(int nr, volatile unsigned long * addr) { __asm__ __volatile__( LOCK_PREFIX "btrl %1,%0" :"+m" (ADDR) :"Ir" (nr)); } Thanks!