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Message-Id: <20240930105710.383284-4-jonas.oberhauser@huaweicloud.com>
Date: Mon, 30 Sep 2024 12:57:08 +0200
From: Jonas Oberhauser <jonas.oberhauser@...weicloud.com>
To: paulmck@...nel.org
Cc: stern@...land.harvard.edu,
parri.andrea@...il.com,
will@...nel.org,
peterz@...radead.org,
boqun.feng@...il.com,
npiggin@...il.com,
dhowells@...hat.com,
j.alglave@....ac.uk,
luc.maranget@...ia.fr,
akiyks@...il.com,
dlustig@...dia.com,
joel@...lfernandes.org,
urezki@...il.com,
quic_neeraju@...cinc.com,
frederic@...nel.org,
linux-kernel@...r.kernel.org,
lkmm@...ts.linux.dev,
hernan.poncedeleon@...weicloud.com,
Jonas Oberhauser <jonas.oberhauser@...weicloud.com>,
Viktor Vafeiadis <viktor@...-sws.org>
Subject: [PATCH v4 3/5] 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@...-sws.org>
Suggested-by: Alan Stern <stern@...land.harvard.edu>
Signed-off-by: Jonas Oberhauser <jonas.oberhauser@...weicloud.com>
---
tools/memory-model/linux-kernel.cat | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/tools/memory-model/linux-kernel.cat b/tools/memory-model/linux-kernel.cat
index adf3c4f41229..d7e7bf13c831 100644
--- 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]) |
--
2.34.1
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