Messages in this thread | | | Date | Tue, 06 Apr 2010 13:11:12 -0700 | From | "H. Peter Anvin" <> | Subject | Re: in x86 architecture ,why the function atomic_sub_and_test() does not disable the interrupt? |
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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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