Messages in this thread | | | Date | Fri, 25 Jan 2013 19:29:24 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH] generic dynamic per cpu refcounting |
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On 01/25, Oleg Nesterov wrote: > > > +void __percpu_ref_get(struct percpu_ref *ref, bool alloc) > > +{ > > + unsigned long pcpu_count; > > + uint64_t v; > > + > > + pcpu_count = ACCESS_ONCE(ref->pcpu_count); > > + > > + if (REF_STATUS(pcpu_count) == PCPU_REF_PTR) { > > + /* for rcu - we're not using rcu_dereference() */ > > + smp_read_barrier_depends(); > > + __this_cpu_inc(*((unsigned __percpu *) pcpu_count)); > > The comment looks confusing a bit... smp_read_barrier_depends() is not > for rcu, we obviously need it to access (unsigned __percpu *) pcpu_count. > But yes, since we didn't use rcu_dereference() we have to add it by hand.
Hmm. Otoh, arch/alpha uses asm-generic/percpu.h so in theory we need smp_read_barrier_depends() after __this_cpu_generic_to_op() calculates the "real" pointer, __this_cpu_ptr() ?
Just curious...
Oleg.
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