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

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Date:   Fri, 4 Sep 2020 12:56:04 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Boqun Feng <boqun.feng@...il.com>
Cc:     peterz@...radead.org, 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,
        npiggin@...il.com, dhowells@...hat.com, j.alglave@....ac.uk,
        luc.maranget@...ia.fr, akiyks@...il.com
Subject: Re: [PATCH kcsan 6/9] tools/memory-model: Expand the cheatsheet.txt
 notion of relaxed

On Fri, Sep 04, 2020 at 10:47:17AM +0800, Boqun Feng wrote:
> On Thu, Sep 03, 2020 at 07:39:55PM -0700, Paul E. McKenney wrote:
> > 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.
> > 
> 
> Looks good to me ;-)
> 
> 
> Acked-by: Boqun Feng <boqun.feng@...il.com>

Applied, thank you!

							Thanx, Paul

> Regards,
> Boqun
> 
> > 							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