Messages in this thread | | | Subject | Re: [PATCH] udev enhancements to use kernel event queue | From | Robert Love <> | Date | 12 Jun 2003 16:42:04 -0700 |
| |
On Thu, 2003-06-12 at 16:34, Patrick Mochel wrote:
> > Nice thinking. It is a shame we need a lock for this, but we don't > > have an atomic_inc_and_return(). > > Those were my sentiments exactly:
Heh.
> +static inline int atomic_inc_and_read(atomic_t *v) > +{ > + __asm__ __volatile__( > + LOCK "incl %0" > + :"=m" (v->counter) > + :"m" (v->counter)); > + return v->counter; > +}
What prevents a race between the increment and the return (i.e. you return v->counter after another person also increments it)? Only the increment is guaranteed atomic.
I think you need to copy the result of the increment into a local variable _inside_ of the LOCK and return that. Whether or not that will work sanely on all architectures I dunno.
Robert Love
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |