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SubjectRe: in x86 architecture ,why the function atomic_sub_and_test() does not disable the interrupt?
On 04/05/2010 11:07 PM, Roland Dreier wrote:
> > static inline int atomic_sub_and_test(int i, atomic_t *v)
> > {
> > unsigned char c;
> >
> > asm volatile(LOCK_PREFIX "subl %2,%0; sete %1"
> > : "+m" (v->counter), "=qm" (c)
> > : "ir" (i) : "memory");
> > return c;
> > }
>
> Why would disabling interrupts be necessary? The LOCK_PREFIX makes the
> subl atomic, and the sete just operates using the flag set by subl, so
> it doesn't matter if any interrupts occur or not (since returning from
> an interrupt must obviously restore flags).

Even without the LOCK prefix, subl would be atomic against local
interrupts. The LOCK prefix is only necessary to make it atomic against
other processors.

-hpa


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