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SubjectRe: [PATCH] lockdep: Add a document describing crossrelease feature
On Wed, Jul 06, 2016 at 02:33:29PM +0900, Byungchul Park wrote:
> On Wed, Jul 06, 2016 at 11:17:10AM +0900, Byungchul Park wrote:
> >
> > lock(A)
> > wait_for(B)
> > ~~~~~~~~~~~~~~~~~~~~~~~~ <- serialized by atomic operation
> > lock(A)
> > unlock(A)
> > wake(B)
> > unlock(A)
>
> By the way, I have a question. Is there anyone who could answer it?
>
> I want to serialize between two context's lock operations, for example,
>
> context A context B
> -------------- --------------
> lock A
> lock B ...
> lock C
> atomic_inc_return
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ <- serialization
> atomic_read
> lock D
> ... lock E
> lock F
>
> so that we can see these in the order like A -> B -> C -> D -> E -> F.
>
> atomic_inc_return() is used after lock C in context A, and atomic_read()
> is used before lock D in context B. And I want to make it serialized when
> the atomic_read() can see the increased value.
>
> Can I use smp_mb__after_atomic() just after atomic_read()

No. atomic_set() and atomic_read() are not RmW operations.

> or should I use
> smp_mb()? I think anyway I have to choose one of them for that ordering.

smp_load_acquire(), if that observes the increment it will ensure D
comes after etc..

Also, atomic_read() _could_ be enough, if its part of a control
dependency, because LOCK very much involves a store, so the load->store
order provided by the control dependency will already order things.

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