Messages in this thread | | | Date | Wed, 21 Feb 2018 10:14:10 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] tools/memory-model: update: remove rb-dep, smp_read_barrier_depends, and lockless_dereference |
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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} ; } > > >
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