Re: [PATCH v2] ipc/mqueue: remove STATE_PENDING

From: Davidlohr Bueso
Date: Tue Apr 28 2015 - 12:59:38 EST

On Tue, 2015-04-28 at 18:43 +0200, Peter Zijlstra wrote:
> Well, if you can 'guarantee' the cmpxchg will not fail, you can then
> rely on the fact that cmpxchg implies a full barrier, which would
> obviate the need for the wmb.

Yes, assuming it implies barriers on both sides. And we could obviously
remove the need for pairing. With wake_q being local to wq_sleep() I
cannot see duplicate tasks trying to add themselves in the list. Failed
cmpxchg should only occur when users start misusing the wake_q.

Manfred, do you have any objections to this? Perhaps I've missed the
real purpose of the barriers.


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