linux-kernel - [PATCH tip/core/rcu 1/3] tools/memory-model: Tie acquire loads to reads-from

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Date:   Wed,  6 Jan 2021 09:36:36 -0800
From:   paulmck@...nel.org
To:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        kernel-team@...com, mingo@...nel.org
Cc:     stern@...land.harvard.edu, parri.andrea@...il.com, will@...nel.org,
        peterz@...radead.org, boqun.feng@...il.com, npiggin@...il.com,
        dhowells@...hat.com, j.alglave@....ac.uk, luc.maranget@...ia.fr,
        akiyks@...il.com, "Paul E. McKenney" <paulmck@...nel.org>
Subject: [PATCH tip/core/rcu 1/3] tools/memory-model: Tie acquire loads to reads-from

From: "Paul E. McKenney" <paulmck@...nel.org>

This commit explicitly makes the connection between acquire loads and
the reads-from relation.  It also adds an entry for happens-before,
and refers to the corresponding section of explanation.txt.

Reported-by: Boqun Feng <boqun.feng@...il.com>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 tools/memory-model/Documentation/glossary.txt | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/tools/memory-model/Documentation/glossary.txt b/tools/memory-model/Documentation/glossary.txt
index 79acb75..b2da636 100644
--- a/tools/memory-model/Documentation/glossary.txt
+++ b/tools/memory-model/Documentation/glossary.txt
@@ -33,10 +33,11 @@ Acquire:  With respect to a lock, acquiring that lock, for example,
 	acquire loads.
 
 	When an acquire load returns the value stored by a release store
-	to that same variable, then all operations preceding that store
-	happen before any operations following that load acquire.
+	to that same variable, (in other words, the acquire load "reads
+	from" the release store), then all operations preceding that
+	store "happen before" any operations following that load acquire.
 
-	See also "Relaxed" and "Release".
+	See also "Happens-Before", "Reads-From", "Relaxed", and "Release".
 
 Coherence (co):  When one CPU's store to a given variable overwrites
 	either the value from another CPU's store or some later value,
@@ -119,6 +120,11 @@ Fully Ordered:  An operation such as smp_mb() that orders all of
 	that orders all of its CPU's prior accesses, itself, and
 	all of its CPU's subsequent accesses.
 
+Happens-Before (hb): A relation between two accesses in which LKMM
+	guarantees the first access precedes the second.  For more
+	detail, please see the "THE HAPPENS-BEFORE RELATION: hb"
+	section of explanation.txt.
+
 Marked Access:  An access to a variable that uses an special function or
 	macro such as "r1 = READ_ONCE(x)" or "smp_store_release(&a, 1)".
 
-- 
2.9.5