Synchronizing auxiliary mutex data

[Andreas Schwab]

On Jun 20 2017, Torvald Riegel <triegel@redhat.com> wrote:

> You were talking about ordering of the writes. to __owner.  This happens
> through the happens-before established through the unlock->lock
> synchronization.  Specifically, in unlock:
>   store(&owner, 0, mo_relaxed) ->sb store(&lock, 0, mo_release)
> and in lock:
>   cas(&lock, expect==0, new==1, mo_acquire)==success
>     ->sb store(&owner, TID, mo_relaxed)
> where ->sb is sequenced-before, so essentially program order.  The CAS
> that succeeds is a load too that reads-from the store in unlock that
> writes 0.

I don't understand how writing to lock has any influence on the access
to owner.  What guarantees that the modification of owner in the
unlocking thread is seen by the locking thread?

Andreas.

-- 
Andreas Schwab, SUSE Labs, schwab@suse.de
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