Re: [PATCH v8 4/4] qrwlock: Use smp_store_release() in write_unlock()

From: Peter Zijlstra
Date: Tue Jan 21 2014 - 10:41:48 EST

On Tue, Jan 21, 2014 at 10:02:06AM -0500, Waiman Long wrote:
> My latest v9 series of qrwlock patch will automatically adapt to the lack of
> atomic byte access by using an atomic integer instruction instead. So the
> new series should work for pre-EV56 Alpha, it is just a bit less efficient
> in this case.

See my other email; I don't think you can do that without also changing
the implementation of the queue_read_{try}lock() functions.

Without those changes you can have transient values in your 'read-count'
part of the word and a full word write will wreck things.
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