On Fri, Nov 06, 2020 at 11:59:30AM -0500, Alan Stern wrote:
> On Thu, Nov 05, 2020 at 02:00:14PM -0800, paulmck@xxxxxxxxxx wrote:
> > From: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
> >
> > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
> > ---
> > 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".
>
> There should also be an entry for "Data Dependency", linked from here
> and from Control Dependency.
>
> > +Marked Access: An access to a variable that uses an special function or
> > + macro such as "r1 = READ_ONCE()" or "smp_store_release(&a, 1)".
>
> How about "r1 = READ_ONCE(x)"?
Good catches! I am planning to squash the commit below into the
original. Does that cover it?
Thanx, Paul
------------------------------------------------------------------------
commit 27c694f5a049d3edac1f258b888d02650cec936a
Author: Paul E. McKenney <paulmck@xxxxxxxxxx>
Date: Fri Nov 6 10:02:41 2020 -0800
squash! tools/memory-model: Add a glossary of LKMM terms
[ paulmck: Apply Alan Stern feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
diff --git a/tools/memory-model/Documentation/glossary.txt b/tools/memory-model/Documentation/glossary.txt
index 383151b..471bf13 100644
--- a/tools/memory-model/Documentation/glossary.txt
+++ b/tools/memory-model/Documentation/glossary.txt
@@ -22,7 +22,7 @@ Address Dependency: When the address of a later memory access is computed
dependencies. Please see Documentation/RCU/rcu_dereference.txt
for more information.
- See also "Control Dependency".
+ See also "Control Dependency" and "Data Dependency".
Acquire: With respect to a lock, acquiring that lock, for example,
using spin_lock(). With respect to a non-lock shared variable,
@@ -109,7 +109,7 @@ Happens-Before (hb): A relation between two accesses in which LKMM
section of explanation.txt.
Marked Access: An access to a variable that uses an special function or
- macro such as "r1 = READ_ONCE()" or "smp_store_release(&a, 1)".
+ macro such as "r1 = READ_ONCE(x)" or "smp_store_release(&a, 1)".
See also "Unmarked Access".
