kcsan: Introduce CONFIG_KCSAN_STRICT

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>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

Author: melver

Documentation/dev-tools/kcsan.rst

@@ -127,6 +127,10 @@ 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
 ~~~~~~~~~~~~~~~~~
 

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