linux-kernel - Re: [PATCH memory-model 5/8] tools/memory-model: Add a glossary of LKMM terms

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Date:   Fri, 6 Nov 2020 09:47:22 +0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     paulmck@...nel.org
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        kernel-team@...com, mingo@...nel.org, stern@...land.harvard.edu,
        parri.andrea@...il.com, will@...nel.org, peterz@...radead.org,
        npiggin@...il.com, dhowells@...hat.com, j.alglave@....ac.uk,
        luc.maranget@...ia.fr, akiyks@...il.com
Subject: Re: [PATCH memory-model 5/8] tools/memory-model: Add a glossary of
 LKMM terms

On Thu, Nov 05, 2020 at 02:00:14PM -0800, paulmck@...nel.org wrote:
> From: "Paul E. McKenney" <paulmck@...nel.org>
> 
> Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> ---
>  tools/memory-model/Documentation/glossary.txt | 155 ++++++++++++++++++++++++++
>  1 file changed, 155 insertions(+)
>  create mode 100644 tools/memory-model/Documentation/glossary.txt
> 
> diff --git a/tools/memory-model/Documentation/glossary.txt b/tools/memory-model/Documentation/glossary.txt
> new file mode 100644
> index 0000000..036fa28
> --- /dev/null
> +++ b/tools/memory-model/Documentation/glossary.txt
> @@ -0,0 +1,155 @@
> +This document contains brief definitions of LKMM-related terms.  Like most
> +glossaries, it is not intended to be read front to back (except perhaps
> +as a way of confirming a diagnosis of OCD), but rather to be searched
> +for specific terms.
> +
> +
> +Address Dependency:  When the address of a later memory access is computed
> +	based on the value returned by an earlier load, an "address
> +	dependency" extends from that load extending to the later access.
> +	Address dependencies are quite common in RCU read-side critical
> +	sections:
> +
> +	 1 rcu_read_lock();
> +	 2 p = rcu_dereference(gp);
> +	 3 do_something(p->a);
> +	 4 rcu_read_unlock();
> +
> +	 In this case, because the address of "p->a" on line 3 is computed
> +	 from the value returned by the rcu_dereference() on line 2, the
> +	 address dependency extends from that rcu_dereference() to that
> +	 "p->a".  In rare cases, optimizing compilers can destroy address
> +	 dependencies.	Please see Documentation/RCU/rcu_dereference.txt
> +	 for more information.
> +
> +	 See also "Control Dependency".
> +
> +Acquire:  With respect to a lock, acquiring that lock, for example,
> +	using spin_lock().  With respect to a non-lock shared variable,
> +	a special operation that includes a load and which orders that
> +	load before later memory references running on that same CPU.
> +	An example special acquire operation is smp_load_acquire(),
> +	but atomic_read_acquire() and atomic_xchg_acquire() also include
> +	acquire loads.
> +
> +	When an acquire load returns the value stored by a release store
> +	to that same variable, then all operations preceding that store

Change this to:

	When an acquire load reads-from a release store

, and put a reference to "Reads-from"? I think this makes the document
more consistent in that it makes clear "an acquire load returns the
value stored by a release store to the same variable" is not a special
case, it's simple a "Reads-from".

> +	happen before any operations following that load acquire.

Add a reference to the definition of "happen before" in explanation.txt?

Regards,
Boqun

> +
> +	See also "Relaxed" and "Release".
> +
[...]