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Date:   Sat, 14 Jan 2023 11:42:32 -0500
From:   Alan Stern <stern@rowland.harvard.edu>
To:     Jonas Oberhauser <jonas.oberhauser@huawei.com>
Cc:     "paulmck@kernel.org" <paulmck@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
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        Kernel development list <linux-kernel@vger.kernel.org>
Subject: Re: Internal vs. external barriers (was: Re: Interesting LKMM litmus
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On Fri, Jan 13, 2023 at 02:55:34PM +0000, Jonas Oberhauser wrote:
> I think the whole rcu-order topic can be summarized as the 'one rule': "if a grace period happens before a rcsc-unlock, it must also happen before the rcsc -lock, and analogously if  rcsc-lock happens before a grace period, the rcsc-unlock also happens before the grace period" . 

There is more to it than that, as I mentioned earlier.  A complete
description can be found the explanation.txt document; it says:

	For any critical section C and any grace period G, at least
	one of the following statements must hold:

(1)	C ends before G does, and in addition, every store that
	propagates to C's CPU before the end of C must propagate to
	every CPU before G ends.

(2)	G starts before C does, and in addition, every store that
	propagates to G's CPU before the start of G must propagate
	to every CPU before C starts.

Alan