[PATCH kcsan 3/8] kcsan: Introduce CONFIG_KCSAN_STRICT

From: Paul E. McKenney
Date: Wed Jul 21 2021 - 17:08:17 EST


From: Marco Elver <elver@xxxxxxxxxx>

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@xxxxxxxxxx>
Acked-by: Mark Rutland <mark.rutland@xxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
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 6a600cf8430b1..69dc9c502ccc5 100644
--- a/Documentation/dev-tools/kcsan.rst
+++ b/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
~~~~~~~~~~~~~~~~~

diff --git a/lib/Kconfig.kcsan b/lib/Kconfig.kcsan
index 5304f211f81f1..c76fbb3ee09ec 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
--
2.31.1.189.g2e36527f23