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tools/memory-model: Redefine rb in terms of rcu-fence

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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>
This commit is contained in:
Alan Stern
2018-05-14 16:33:40 -07:00
committed by Ingo Molnar
parent 1ee2da5f9b
commit 9d036883a1
2 changed files with 128 additions and 71 deletions
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33
tools/memory-model/linux-kernel.cat
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@@ -102,20 +102,27 @@ let rscs = po ; crit^-1 ; po?
*)
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
*)