Re: [PATCH] tools/memory-model: update: remove rb-dep, smp_read_barrier_depends, and lockless_dereference

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Wed, Feb 21, 2018 at 06:58:57PM +0100, Andrea Parri wrote:
> On Wed, Feb 21, 2018 at 12:15:56PM -0500, Alan Stern wrote:
> > Commit bf28ae562744 ("tools/memory-model: Remove rb-dep,
> > smp_read_barrier_depends, and lockless_dereference") was accidentally
> > merged too early, while it was still in RFC form.  This patch adds in
> > the missing pieces.
> > 
> > Akira pointed out some typos in the original patch, and he noted that
> > cheatsheet.txt should be updated to indicate how unsuccessful RMW
> > operations relate to address dependencies.
> > 
> > Andrea pointed out that the macro for rcu_dereference() in linux.def
> > should now use the "once" annotation instead of "deref".  He also
> > suggested that the comments should mention commit 5a8897cc7631
> > ("locking/atomics/alpha: Add smp_read_barrier_depends() to
> > _release()/_relaxed() atomics") as an important precursor, and he
> > contributed commit cb13b424e986 ("locking/xchg/alpha: Add
> > unconditional memory barrier to cmpxchg()"), another prerequisite.
> > 
> > Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
> > Suggested-by: Akira Yokosawa <akiyks@gmail.com>
> > Suggested-by: Andrea Parri <parri.andrea@gmail.com>
> > Fixes: bf28ae562744 ("tools/memory-model: Remove rb-dep, smp_read_barrier_depends, and lockless_dereference")
> 
> Acked-by: Andrea Parri <parri.andrea@gmail.com>

Applied, thank you!

							Thanx, Paul

> Thanks,
>   Andrea
> 
> 
> > 
> > ---
> > 
> >  tools/memory-model/Documentation/cheatsheet.txt  |    6 +++---
> >  tools/memory-model/Documentation/explanation.txt |    4 ++--
> >  tools/memory-model/linux-kernel.def              |    2 +-
> >  3 files changed, 6 insertions(+), 6 deletions(-)
> > 
> > Index: usb-4.x/tools/memory-model/Documentation/cheatsheet.txt
> > ===================================================================
> > --- usb-4.x.orig/tools/memory-model/Documentation/cheatsheet.txt
> > +++ usb-4.x/tools/memory-model/Documentation/cheatsheet.txt
> > @@ -1,11 +1,11 @@
> >                                    Prior Operation     Subsequent Operation
> >                                    ---------------  ---------------------------
> >                                 C  Self  R  W  RWM  Self  R  W  DR  DW  RMW  SV
> > -                              __  ----  -  -  ---  ----  -  -  --  --  ---  --
> > +                              --  ----  -  -  ---  ----  -  -  --  --  ---  --
> >  
> >  Store, e.g., WRITE_ONCE()            Y                                       Y
> > -Load, e.g., READ_ONCE()              Y                              Y        Y
> > -Unsuccessful RMW operation           Y                              Y        Y
> > +Load, e.g., READ_ONCE()              Y                          Y   Y        Y
> > +Unsuccessful 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
> > Index: usb-4.x/tools/memory-model/Documentation/explanation.txt
> > ===================================================================
> > --- usb-4.x.orig/tools/memory-model/Documentation/explanation.txt
> > +++ usb-4.x/tools/memory-model/Documentation/explanation.txt
> > @@ -826,7 +826,7 @@ A-cumulative; they only affect the propa
> >  executed on C before the fence (i.e., those which precede the fence in
> >  program order).
> >  
> > -read_lock(), rcu_read_unlock(), and synchronize_rcu() fences have
> > +read_read_lock(), rcu_read_unlock(), and synchronize_rcu() fences have
> >  other properties which we discuss later.
> >  
> >  
> > @@ -1138,7 +1138,7 @@ final effect is that even though the two
> >  program order, it appears that they aren't.
> >  
> >  This could not have happened if the local cache had processed the
> > -incoming stores in FIFO order.  In constrast, other architectures
> > +incoming stores in FIFO order.  By contrast, other architectures
> >  maintain at least the appearance of FIFO order.
> >  
> >  In practice, this difficulty is solved by inserting a special fence
> > Index: usb-4.x/tools/memory-model/linux-kernel.def
> > ===================================================================
> > --- usb-4.x.orig/tools/memory-model/linux-kernel.def
> > +++ usb-4.x/tools/memory-model/linux-kernel.def
> > @@ -13,7 +13,7 @@ WRITE_ONCE(X,V) { __store{once}(X,V); }
> >  smp_store_release(X,V) { __store{release}(*X,V); }
> >  smp_load_acquire(X) __load{acquire}(*X)
> >  rcu_assign_pointer(X,V) { __store{release}(X,V); }
> > -rcu_dereference(X) __load{deref}(X)
> > +rcu_dereference(X) __load{once}(X)
> >  
> >  // Fences
> >  smp_mb() { __fence{mb} ; }
> > 
>