tools/memory-model: Define effect of Mb tags on RMWs in tools/...

Herd7 transforms successful RMW with Mb tags by inserting smp_mb() fences
around them. We emulate this by considering imaginary po-edges before the
RMW read and before the RMW write, and extending the smp_mb() ordering
rule, which currently only applies to real po edges that would be found
around a really inserted smp_mb(), also to cases of the only imagined po
edges.

Reported-by: Viktor Vafeiadis <viktor@mpi-sws.org>
Suggested-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Jonas Oberhauser <jonas.oberhauser@huaweicloud.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Tested-by: Boqun Feng <boqun.feng@gmail.com>

diff --git a/tools/memory-model/linux-kernel.cat b/tools/memory-model/linux-kernel.cat
index adf3c4f412296269bb9f8127cd7e04f276479a57..d7e7bf13c831be1654d193ab87cc1db9416289c6 100644 (file)
--- a/tools/memory-model/linux-kernel.cat
+++ b/tools/memory-model/linux-kernel.cat
@@ -34,6 +34,16 @@ let R4rmb = R \ Noreturn     (* Reads for which rmb works *)
 let rmb = [R4rmb] ; fencerel(Rmb) ; [R4rmb]
 let wmb = [W] ; fencerel(Wmb) ; [W]
 let mb = ([M] ; fencerel(Mb) ; [M]) |
+       (*
+        * full-barrier RMWs (successful cmpxchg(), xchg(), etc.) act as
+        * though there were enclosed by smp_mb().
+        * The effect of these virtual smp_mb() is formalized by adding
+        * Mb tags to the read and write of the operation, and providing
+        * the same ordering as though there were additional po edges
+        * between the Mb tag and the read resp. write.
+        *)
+       ([M] ; po ; [Mb & R]) |
+       ([Mb & W] ; po ; [M]) |
        ([M] ; fencerel(Before-atomic) ; [RMW] ; po? ; [M]) |
        ([M] ; po? ; [RMW] ; fencerel(After-atomic) ; [M]) |
        ([M] ; po? ; [LKW] ; fencerel(After-spinlock) ; [M]) |