tools/memory-model: Redefine rb in terms of rcu-fence
This patch reorganizes the definition of rb in the Linux Kernel Memory
Consistency Model. The relation is now expressed in terms of
rcu-fence, which consists of a sequence of gp and rscs links separated
by rcu-link links, in which the number of occurrences of gp is >= the
number of occurrences of rscs.
Arguments similar to those published in
http://diy.inria.fr/linux/long.pdf show that rcu-fence behaves like an
inter-CPU strong fence. Furthermore, the definition of rb in terms of
rcu-fence is highly analogous to the definition of pb in terms of
strong-fence, which can help explain why rcu-path expresses a form of
temporal ordering.
This change should not affect the semantics of the memory model, just
its internal organization.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Reviewed-by: Andrea Parri <parri.andrea@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: akiyks@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
Link: http://lkml.kernel.org/r/1526340837-12222-2-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/tools/memory-model/linux-kernel.cat b/tools/memory-model/linux-kernel.cat
index cdf6828..1e5c465 100644
--- a/tools/memory-model/linux-kernel.cat
+++ b/tools/memory-model/linux-kernel.cat
@@ -102,20 +102,27 @@
*)
let rcu-link = hb* ; pb* ; prop
-(* Chains that affect the RCU grace-period guarantee *)
-let gp-link = gp ; rcu-link
-let rscs-link = rscs ; rcu-link
-
(*
- * A cycle containing at least as many grace periods as RCU read-side
- * critical sections is forbidden.
+ * Any sequence containing at least as many grace periods as RCU read-side
+ * critical sections (joined by rcu-link) acts as a generalized strong fence.
*)
-let rec rb =
- gp-link |
- (gp-link ; rscs-link) |
- (rscs-link ; gp-link) |
- (rb ; rb) |
- (gp-link ; rb ; rscs-link) |
- (rscs-link ; rb ; gp-link)
+let rec rcu-fence = gp |
+ (gp ; rcu-link ; rscs) |
+ (rscs ; rcu-link ; gp) |
+ (gp ; rcu-link ; rcu-fence ; rcu-link ; rscs) |
+ (rscs ; rcu-link ; rcu-fence ; rcu-link ; gp) |
+ (rcu-fence ; rcu-link ; rcu-fence)
+
+(* rb orders instructions just as pb does *)
+let rb = prop ; rcu-fence ; hb* ; pb*
irreflexive rb as rcu
+
+(*
+ * The happens-before, propagation, and rcu constraints are all
+ * expressions of temporal ordering. They could be replaced by
+ * a single constraint on an "executes-before" relation, xb:
+ *
+ * let xb = hb | pb | rb
+ * acyclic xb as executes-before
+ *)