Messages in this thread | | | From | Paul Mackerras <> | Date | Fri, 13 Jun 2003 09:40:23 +1000 (EST) | Subject | Re: [PATCH] udev enhancements to use kernel event queue |
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Patrick Mochel writes:
> It seems like the following should work. Would someone mind commenting on > it?
> +/** > + * atomic_inc_and_read - increment atomic variable and return new value > + * @v: pointer of type atomic_t > + * > + * Atomically increments @v by 1. Note that the guaranteed > + * useful range of an atomic_t is only 24 bits. > + */ > +static inline int atomic_inc_and_read(atomic_t *v) > +{ > + __asm__ __volatile__( > + LOCK "incl %0" > + :"=m" (v->counter) > + :"m" (v->counter)); > + return v->counter; > +}
BZZZT. If another CPU is also doing atomic_inc_and_read you could end up with both calls returning the same value.
You can't do atomic_inc_and_read on 386. You can on cpus that have cmpxchg (e.g. later x86). You can also on machines with load-locked and store-conditional instructions (alpha, ppc, probably most other RISCs).
Paul.
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