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Date:   Mon,  7 Jun 2021 14:56:49 +0200
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Subject: [PATCH 3/7] kcsan: Introduce CONFIG_KCSAN_STRICT
From:   Marco Elver <elver@google.com>
To:     elver@google.com, paulmck@kernel.org
Cc:     boqun.feng@gmail.com, mark.rutland@arm.com, will@kernel.org,
        glider@google.com, dvyukov@google.com, kasan-dev@googlegroups.com,
        linux-kernel@vger.kernel.org
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Add a simpler Kconfig variable to configure KCSAN's "strict" mode. This
makes it simpler in documentation or messages to suggest just a single
configuration option to select the strictest checking mode (vs.
currently having to list several options).

Signed-off-by: Marco Elver <elver@google.com>
---
 Documentation/dev-tools/kcsan.rst |  4 ++++
 lib/Kconfig.kcsan                 | 10 ++++++++++
 2 files changed, 14 insertions(+)

diff --git a/Documentation/dev-tools/kcsan.rst b/Documentation/dev-tools/kcsan.rst
index ba059df10b7d..17f974213b88 100644
--- a/Documentation/dev-tools/kcsan.rst
+++ b/Documentation/dev-tools/kcsan.rst
@@ -124,6 +124,10 @@ Kconfig options:
   causes KCSAN to not report data races due to conflicts where the only plain
   accesses are aligned writes up to word size.
 
+To use the strictest possible rules, select ``CONFIG_KCSAN_STRICT=y``, which
+configures KCSAN to follow the Linux-kernel memory consistency model (LKMM) as
+closely as possible.
+
 DebugFS interface
 ~~~~~~~~~~~~~~~~~
 
diff --git a/lib/Kconfig.kcsan b/lib/Kconfig.kcsan
index 5304f211f81f..c76fbb3ee09e 100644
--- a/lib/Kconfig.kcsan
+++ b/lib/Kconfig.kcsan
@@ -183,9 +183,17 @@ config KCSAN_REPORT_RACE_UNKNOWN_ORIGIN
 	  reported if it was only possible to infer a race due to a data value
 	  change while an access is being delayed on a watchpoint.
 
+config KCSAN_STRICT
+	bool "Strict data-race checking"
+	help
+	  KCSAN will report data races with the strictest possible rules, which
+	  closely aligns with the rules defined by the Linux-kernel memory
+	  consistency model (LKMM).
+
 config KCSAN_REPORT_VALUE_CHANGE_ONLY
 	bool "Only report races where watcher observed a data value change"
 	default y
+	depends on !KCSAN_STRICT
 	help
 	  If enabled and a conflicting write is observed via a watchpoint, but
 	  the data value of the memory location was observed to remain
@@ -194,6 +202,7 @@ config KCSAN_REPORT_VALUE_CHANGE_ONLY
 config KCSAN_ASSUME_PLAIN_WRITES_ATOMIC
 	bool "Assume that plain aligned writes up to word size are atomic"
 	default y
+	depends on !KCSAN_STRICT
 	help
 	  Assume that plain aligned writes up to word size are atomic by
 	  default, and also not subject to other unsafe compiler optimizations
@@ -206,6 +215,7 @@ config KCSAN_ASSUME_PLAIN_WRITES_ATOMIC
 
 config KCSAN_IGNORE_ATOMICS
 	bool "Do not instrument marked atomic accesses"
+	depends on !KCSAN_STRICT
 	help
 	  Never instrument marked atomic accesses. This option can be used for
 	  additional filtering. Conflicting marked atomic reads and plain
-- 
2.32.0.rc1.229.g3e70b5a671-goog