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tools/memory-model: Finish the removal of rb-dep, smp_read_barrier_depends(), and lockless_dereference() 

Commit:

  bf28ae5627 ("tools/memory-model: Remove rb-dep, smp_read_barrier_depends, and lockless_dereference")

was 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.

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:

  5a8897cc76 ("locking/atomics/alpha: Add smp_read_barrier_depends() to _release()/_relaxed() atomics")

... as an important precursor, and he contributed commit:

  cb13b424e9 ("locking/xchg/alpha: Add unconditional memory barrier to cmpxchg()")

which is another prerequisite.

Suggested-by: Akira Yokosawa <akiyks@gmail.com>
Suggested-by: Andrea Parri <parri.andrea@gmail.com>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
[ Fixed read_read_lock() typo reported by Akira. ]
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Andrea Parri <parri.andrea@gmail.com>
Acked-by: Akira Yokosawa <akiyks@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: boqun.feng@gmail.com
Cc: dhowells@redhat.com
Cc: j.alglave@ucl.ac.uk
Cc: linux-arch@vger.kernel.org
Cc: luc.maranget@inria.fr
Cc: npiggin@gmail.com
Cc: will.deacon@arm.com
Fixes: bf28ae5627 ("tools/memory-model: Remove rb-dep, smp_read_barrier_depends, and lockless_dereference")
Link: http://lkml.kernel.org/r/1520443660-16858-4-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Alan Stern 2018-03-07 09:27:40 -08:00 committed by Ingo Molnar
parent ff1fe5e079
commit bd5c0ba2cd
3 changed files with 6 additions and 6 deletions
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6
tools/memory-model/Documentation/cheatsheet.txt
View File

@ -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

4
tools/memory-model/Documentation/explanation.txt
View File

@ -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
rcu_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 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

2
tools/memory-model/linux-kernel.def
View File

@ -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} ; }