linux-kernel - [PATCH] tools/memory-model: update: remove rb-dep, smp_read_barrier_depends, and lockless

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Date:   Wed, 21 Feb 2018 12:15:56 -0500 (EST)
From:   Alan Stern <stern@...land.harvard.edu>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
cc:     Andrea Parri <parri.andrea@...il.com>,
        Akira Yokosawa <akiyks@...il.com>,
        Kernel development list <linux-kernel@...r.kernel.org>,
        <mingo@...nel.org>, Will Deacon <will.deacon@....com>,
        <peterz@...radead.org>, <boqun.feng@...il.com>,
        <npiggin@...il.com>, <dhowells@...hat.com>,
        Jade Alglave <j.alglave@....ac.uk>,
        Luc Maranget <luc.maranget@...ia.fr>,
        Patrick Bellasi <patrick.bellasi@....com>
Subject: [PATCH] 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 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@...land.harvard.edu>
Suggested-by: Akira Yokosawa <akiyks@...il.com>
Suggested-by: Andrea Parri <parri.andrea@...il.com>
Fixes: bf28ae562744 ("tools/memory-model: Remove rb-dep, smp_read_barrier_depends, and lockless_dereference")

---

 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} ; }