Messages in this thread | | | Subject | Re: [PATCH] tools/memory-model: update: remove rb-dep, smp_read_barrier_depends, and lockless_dereference | From | Akira Yokosawa <> | Date | Sun, 25 Feb 2018 07:47:23 +0900 |
| |
On 2018/02/24 10:08:14 -0800, Paul E. McKenney wrote: > On Sat, Feb 24, 2018 at 11:49:20AM -0500, Alan Stern wrote: >> On Sat, 24 Feb 2018, Andrea Parri wrote: >> >>> On Fri, Feb 23, 2018 at 07:30:13PM -0800, Paul E. McKenney wrote: >>>> On Sat, Feb 24, 2018 at 12:22:24PM +0900, Akira Yokosawa wrote: >>>>> On 2018/02/22 07:29:02 +0900, Akira Yokosawa wrote: >>>>>> On 2018/02/22 2:15, Alan Stern wrote: >>> >>> [...] >>> >>>>>>> >>>>>>> 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. >>>>>> >>>>>> My point was to separate unannotated loads from READ_ONCE(), if the >>>>>> cheatsheet should concern such accesses as well. >>>>>> Unsuccessful RMW operations were brought up by Andrea. >>>>>> >>>>> >>>>> Paul, can you amend above paragraph in the change log to something like: >>>>> >>>>> Akira pointed out some typos in the original patch, and he noted that >>>>> cheatsheet.txt should be updated to indicate READ_ONCE() implies >>>>> address dependency, which invited Andrea's observation that it should >>>>> also be updated to indicate how unsuccessful RMW operations relate to >>>>> address dependencies. >>>>> >>>>> , if Alan and Andrea are OK with the amendment. >>>>> >>>>> Also, please append my Acked-by. >>>>> >>>>> Acked-by: Akira Yokosawa <akiyks@gmail.com> >>>> >>>> I can still amend this, and have added your Acked-by. If Alan and Andrea >>>> OK with your change, I will apply that also. >>> >>> LGTM. Thanks, >> >> Me too. > > Very good, how about this for the new version? > > Thanx, Paul > > ------------------------------------------------------------------------ > > commit 21ede43970e50b7397420f17ed08bb02c187e2eb > Author: Alan Stern <stern@rowland.harvard.edu> > Date: Wed Feb 21 12:15:56 2018 -0500 > > tools/memory-model: Update: Remove rb-dep, smp_read_barrier_depends, and lockless_dereference > > 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 indicate that READ_ONCE() now implies an address > dependency. Andrea suggested documenting the relationship betwwen > unsuccessful RMW operations and address dependencies.
Looks good. But I've found a remaining typo in the patch. See below.
> > 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> > Acked-by: Akira Yokosawa <akiyks@gmail.com> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > > diff --git a/tools/memory-model/Documentation/cheatsheet.txt b/tools/memory-model/Documentation/cheatsheet.txt > index 04e458acd6d4..956b1ae4aafb 100644 > --- a/tools/memory-model/Documentation/cheatsheet.txt > +++ b/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 > diff --git a/tools/memory-model/Documentation/explanation.txt b/tools/memory-model/Documentation/explanation.txt > index dae8b8cb2ad3..889fabef7d83 100644 > --- a/tools/memory-model/Documentation/explanation.txt > +++ b/tools/memory-model/Documentation/explanation.txt > @@ -826,7 +826,7 @@ A-cumulative; they only affect the propagation of stores that are > 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
rcu_read_lock()
Don't ask why I missed this in the first place...
Paul, can you fix this directly?
Thanks, Akira
> other properties which we discuss later. > > > @@ -1138,7 +1138,7 @@ final effect is that even though the two loads really are executed in > 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 > diff --git a/tools/memory-model/linux-kernel.def b/tools/memory-model/linux-kernel.def > index 5dfb9c7f3462..397e4e67e8c8 100644 > --- a/tools/memory-model/linux-kernel.def > +++ b/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} ; } >
| |