Re: [PATCH] Fixes for RCU handling of task_struct

[Nick Piggin <nickpiggin@yahoo.com.au>]

Andrew Morton wrote:

> > +static inline int get_task_struct_rcu(struct task_struct *t)
> > +{
> > +	int oldusage;
> > +
> > +	do {
> > +		oldusage = atomic_read(&t->usage);
> > +		if (oldusage == 0) {
> > +			return 0;
> > +		}
> > +	} while (cmpxchg(&t->usage.counter,
> > +		 oldusage, oldusage + 1) != oldusage);
> > +	return 1;
> > +}
>
>
> arm (at least) does not implement cmpxchg.

Yes, and using atomic_t.counter in generic code is ugly, albeit
compatible with all current implementations.

> I think Nick is working on patches which implement cmpxchg on all
> architectures?

Yes, it is basically ready to go.

--
SUSE Labs, Novell Inc.

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