Re: [PATCH kcsan 6/9] tools/memory-model: Expand the cheatsheet.txt notion of relaxed

Paul E. McKenney
2020-09-04T02:40:02Z

On Fri, Sep 04, 2020 at 08:59:21AM +0800, Boqun Feng wrote:
> On Thu, Sep 03, 2020 at 04:30:37PM -0700, Paul E. McKenney wrote:

[ . . . ]

> > How about like this, adding "Relaxed" to the WRITE_ONCE() and READ_ONCE()
> > rows and "RMW" to the "Relaxed operation" row?
> >
>
> Much better now, thanks! However ...
>
> > The file contents are followed by a diff against the previous version.
> >
> > Thanx, Paul
> >
> > ------------------------------------------------------------------------

[ . . . ]

> > Key: Relaxed: A relaxed operation is either a *_relaxed() RMW
> > operation, an unsuccessful RMW operation, READ_ONCE(),
> > WRITE_ONCE(), or one of the atomic_read() and
> > atomic_set() family of operations.
>
> And:
> a RMW operation that doesn't return any value (e.g
> atomic_inc()), IOW it's a void Relaxed operation.

Good point! Please see below.

Thanx, Paul

------------------------------------------------------------------------

Prior Operation Subsequent Operation
--------------- ---------------------------
C Self R W RMW Self R W DR DW RMW SV
-- ---- - - --- ---- - - -- -- --- --

Relaxed store Y Y
Relaxed load Y Y Y Y
Relaxed RMW operation Y Y Y Y
rcu_dereference() Y Y Y Y
Successful *_acquire() R Y Y Y Y Y Y
Successful *_release() C Y Y Y W Y
smp_rmb() Y R Y Y R
smp_wmb() Y W Y Y W
smp_mb() & synchronize_rcu() CP Y Y Y Y Y Y Y Y
Successful full non-void RMW CP Y Y Y Y Y Y Y Y Y Y Y
smp_mb__before_atomic() CP Y Y Y a a a a Y
smp_mb__after_atomic() CP a a Y Y Y Y Y Y

Key: Relaxed: A relaxed operation is either READ_ONCE(), WRITE_ONCE(),
a *_relaxed() RMW operation, an unsuccessful RMW
operation, a non-value-returning RMW operation such
as atomic_inc(), or one of the atomic*_read() and
atomic*_set() family of operations.
C: Ordering is cumulative
P: Ordering propagates
R: Read, for example, READ_ONCE(), or read portion of RMW
W: Write, for example, WRITE_ONCE(), or write portion of RMW
Y: Provides ordering
a: Provides ordering given intervening RMW atomic operation
DR: Dependent read (address dependency)
DW: Dependent write (address, data, or control dependency)
RMW: Atomic read-modify-write operation
SELF: Orders self, as opposed to accesses before and/or after
SV: Orders later accesses to the same variable

------------------------------------------------------------------------

diff --git a/tools/memory-model/Documentation/cheatsheet.txt b/tools/memory-model/Documentation/cheatsheet.txt
index 4146b8d..99d0087 100644
--- a/tools/memory-model/Documentation/cheatsheet.txt
+++ b/tools/memory-model/Documentation/cheatsheet.txt
@@ -17,10 +17,11 @@ smp_mb__before_atomic() CP Y Y Y a a a a Y
smp_mb__after_atomic() CP a a Y Y Y Y Y Y

-Key: Relaxed: A relaxed operation is either a *_relaxed() RMW
- operation, an unsuccessful RMW operation, READ_ONCE(),
- WRITE_ONCE(), or one of the atomic_read() and
- atomic_set() family of operations.
+Key: Relaxed: A relaxed operation is either READ_ONCE(), WRITE_ONCE(),
+ a *_relaxed() RMW operation, an unsuccessful RMW
+ operation, a non-value-returning RMW operation such
+ as atomic_inc(), or one of the atomic*_read() and
+ atomic*_set() family of operations.
C: Ordering is cumulative
P: Ordering propagates
R: Read, for example, READ_ONCE(), or read portion of RMW