Re: Commit 81a43adae3b9 (locking/mutex: Use acquire/release semantics) causing failures on arm64 (ThunderX)

From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: Commit 81a43adae3b9 (locking/mutex: Use acquire/release semantics) causing failures on arm64 (ThunderX)
Date	2015-12-14 21:40 +0100
Message-ID	<qFI4x-2Ex-5@gated-at.bofh.it> (permalink)
References	(5 earlier) <qEuZI-4cP-1@gated-at.bofh.it> <qEw5t-52w-45@gated-at.bofh.it> <qEwf8-57t-11@gated-at.bofh.it> <qEEw3-261-37@gated-at.bofh.it> <qFGvL-1yD-13@gated-at.bofh.it>
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On Mon, Dec 14, 2015 at 06:49:31PM +0000, One Thousand Gnomes wrote:
> 
> But seriously are there any cases we actually care about this for osq ?

So I think what PaulMck is worried about is that one would expect things
like:

	mutex_lock();
	MMIO(++var);
	mutex_unlock();

(the same example Linus gave but with a mutex instead of a spinlock) to
just work.

Now, I haven't checked the code, but I'm not sure we ever rely on osq to
provide the mutex ACQUIRE barrier, since we always need to acquire the
mutex variable itself after we've acquired the osq 'lock'.

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Thread

Re: Commit 81a43adae3b9 (locking/mutex: Use acquire/release  semantics) causing failures on arm64 (ThunderX) One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk> - 2015-12-14 20:00 +0100
  Re: Commit 81a43adae3b9 (locking/mutex: Use acquire/release  semantics) causing failures on arm64 (ThunderX) Peter Zijlstra <peterz@infradead.org> - 2015-12-14 21:40 +0100
  Re: Commit 81a43adae3b9 (locking/mutex: Use acquire/release  semantics) causing failures on arm64 (ThunderX) "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-12-15 07:20 +0100

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