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authorMarco Elver <elver@google.com>2020-02-04 18:21:10 +0100
committerIngo Molnar <mingo@kernel.org>2020-03-21 09:42:18 +0100
commit1e6ee2f0fe8ae682757960edf455e99f611268a0 (patch)
treea7325816ac12d8f67d39f356aad32395e8344175 /lib
parent7ad900d35b49af5a05f595d2274c32e69e01b055 (diff)
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kcsan: Add option to assume plain aligned writes up to word size are atomic
This adds option KCSAN_ASSUME_PLAIN_WRITES_ATOMIC. If enabled, plain aligned writes up to word size are assumed to be atomic, and also not subject to other unsafe compiler optimizations resulting in data races. This option has been enabled by default to reflect current kernel-wide preferences. Signed-off-by: Marco Elver <elver@google.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'lib')
-rw-r--r--lib/Kconfig.kcsan27
1 files changed, 20 insertions, 7 deletions
diff --git a/lib/Kconfig.kcsan b/lib/Kconfig.kcsan
index 3552990abcfe..66126853dab0 100644
--- a/lib/Kconfig.kcsan
+++ b/lib/Kconfig.kcsan
@@ -91,13 +91,13 @@ config KCSAN_REPORT_ONCE_IN_MS
limiting reporting to avoid flooding the console with reports.
Setting this to 0 disables rate limiting.
-# Note that, while some of the below options could be turned into boot
-# parameters, to optimize for the common use-case, we avoid this because: (a)
-# it would impact performance (and we want to avoid static branch for all
-# {READ,WRITE}_ONCE, atomic_*, bitops, etc.), and (b) complicate the design
-# without real benefit. The main purpose of the below options is for use in
-# fuzzer configs to control reported data races, and they are not expected
-# to be switched frequently by a user.
+# The main purpose of the below options is to control reported data races (e.g.
+# in fuzzer configs), and are not expected to be switched frequently by other
+# users. We could turn some of them into boot parameters, but given they should
+# not be switched normally, let's keep them here to simplify configuration.
+#
+# The defaults below are chosen to be very conservative, and may miss certain
+# bugs.
config KCSAN_REPORT_RACE_UNKNOWN_ORIGIN
bool "Report races of unknown origin"
@@ -116,6 +116,19 @@ config KCSAN_REPORT_VALUE_CHANGE_ONLY
the data value of the memory location was observed to remain
unchanged, do not report the data race.
+config KCSAN_ASSUME_PLAIN_WRITES_ATOMIC
+ bool "Assume that plain aligned writes up to word size are atomic"
+ default y
+ help
+ Assume that plain aligned writes up to word size are atomic by
+ default, and also not subject to other unsafe compiler optimizations
+ resulting in data races. This will cause KCSAN to not report data
+ races due to conflicts where the only plain accesses are aligned
+ writes up to word size: conflicts between marked reads and plain
+ aligned writes up to word size will not be reported as data races;
+ notice that data races between two conflicting plain aligned writes
+ will also not be reported.
+
config KCSAN_IGNORE_ATOMICS
bool "Do not instrument marked atomic accesses"
help