On 2018/02/22 2:15, 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.
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.
>
> 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 <st...@rowland.harvard.edu>
> Suggested-by: Akira Yokosawa <aki...@gmail.com>
> Suggested-by: Andrea Parri <parri.and...@gmail.com>
> Fixes: bf28ae562744 ("tools/memory-model: Remove rb-dep,
> smp_read_barrier_depends, and lockless_dereference")
>
The change itself looks good to me.
Acked-by: Akira Yokosawa <aki...@gmail.com>
Thanks, Akira
> ---
>
> 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} ; }
>
