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

    Queued, thank you!

    Thanx, Paul

    > ---
    >
    > 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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