Kent Overstreet <koverstr...@google.com> writes:
> This implements a refcount with similar semantics to
> atomic_get()/atomic_dec_and_test() - but percpu.
>
> It also implements two stage shutdown, as we need it to tear down the
> percpu counts. Before dropping the initial refcount, you must call
> percpu_ref_kill(); this puts the refcount in "shutting down mode" and
> switches back to a single atomic refcount with the appropriate barriers
> (synchronize_rcu()).
>
> It's also legal to call percpu_ref_kill() multiple times - it only returns
> true once, so callers don't have to reimplement shutdown synchronization.
> +static inline void percpu_ref_get(struct percpu_ref *ref)
> +{
> + unsigned __percpu *pcpu_count;
> +
> + preempt_disable();
> +
> + pcpu_count = ACCESS_ONCE(ref->pcpu_count);
> +
> + if (likely(REF_STATUS(pcpu_count) == PCPU_REF_PTR))
> + __this_cpu_inc(*pcpu_count);
> + else
> + atomic_inc(&ref->count);
> +
> + preempt_enable();
> +}
I think this should be rcu_read_lock(), which is currently equivalent
but theoretically different.
Does your percpu_ref_kill() *really* need to be nonblocking? (I'd have
to read your other patches which use this to be sure). Otherwise, just
use synchronize_rcu(), and get rid of the release function...
Cheers,
Rusty.
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