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authorLinus Torvalds <torvalds@linux-foundation.org>2021-09-02 13:00:15 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2021-09-02 13:00:15 -0700
commitaa829778b16f15266fefe2640f04931b16ce39c0 (patch)
treeeb2bc83c849f0461ffd09d4cd5e79036ff469551 /lib
parentaef4892a63c248c31718d23941536b86829a49f0 (diff)
parent4812c9111220b0af00f7a436cc02ffaed289962c (diff)
Merge tag 'locking-debug-2021-09-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull memory model updates from Ingo Molnar: "LKMM updates: - Update documentation and code example KCSAN updates: - Introduce CONFIG_KCSAN_STRICT (which RCU uses) - Optimize use of get_ctx() by kcsan_found_watchpoint() - Rework atomic.h into permissive.h - Add the ability to ignore writes that change only one bit of a given data-racy variable. - Improve comments" * tag 'locking-debug-2021-09-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: tools/memory-model: Document data_race(READ_ONCE()) tools/memory-model: Heuristics using data_race() must handle all values tools/memory-model: Add example for heuristic lockless reads tools/memory-model: Make read_foo_diagnostic() more clearly diagnostic kcsan: Make strict mode imply interruptible watchers kcsan: permissive: Ignore data-racy 1-bit value changes kcsan: Print if strict or non-strict during init kcsan: Rework atomic.h into permissive.h kcsan: Reduce get_ctx() uses in kcsan_found_watchpoint() kcsan: Introduce CONFIG_KCSAN_STRICT kcsan: Remove CONFIG_KCSAN_DEBUG kcsan: Improve some Kconfig comments
Diffstat (limited to 'lib')
-rw-r--r--lib/Kconfig.kcsan42
1 files changed, 30 insertions, 12 deletions
diff --git a/lib/Kconfig.kcsan b/lib/Kconfig.kcsan
index 0440f373248e..e0a93ffdef30 100644
--- a/lib/Kconfig.kcsan
+++ b/lib/Kconfig.kcsan
@@ -40,10 +40,14 @@ menuconfig KCSAN
if KCSAN
-# Compiler capabilities that should not fail the test if they are unavailable.
config CC_HAS_TSAN_COMPOUND_READ_BEFORE_WRITE
def_bool (CC_IS_CLANG && $(cc-option,-fsanitize=thread -mllvm -tsan-compound-read-before-write=1)) || \
(CC_IS_GCC && $(cc-option,-fsanitize=thread --param tsan-compound-read-before-write=1))
+ help
+ The compiler instruments plain compound read-write operations
+ differently (++, --, +=, -=, |=, &=, etc.), which allows KCSAN to
+ distinguish them from other plain accesses. This is currently
+ supported by Clang 12 or later.
config KCSAN_VERBOSE
bool "Show verbose reports with more information about system state"
@@ -58,9 +62,6 @@ config KCSAN_VERBOSE
generated from any one of them, system stability may suffer due to
deadlocks or recursion. If in doubt, say N.
-config KCSAN_DEBUG
- bool "Debugging of KCSAN internals"
-
config KCSAN_SELFTEST
bool "Perform short selftests on boot"
default y
@@ -149,7 +150,8 @@ config KCSAN_SKIP_WATCH_RANDOMIZE
KCSAN_WATCH_SKIP.
config KCSAN_INTERRUPT_WATCHER
- bool "Interruptible watchers"
+ bool "Interruptible watchers" if !KCSAN_STRICT
+ default KCSAN_STRICT
help
If enabled, a task that set up a watchpoint may be interrupted while
delayed. This option will allow KCSAN to detect races between
@@ -169,13 +171,9 @@ config KCSAN_REPORT_ONCE_IN_MS
reporting to avoid flooding the console with reports. Setting this
to 0 disables rate limiting.
-# 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.
+# The main purpose of the below options is to control reported data races, and
+# are not expected to be switched frequently by non-testers or at runtime.
+# The defaults are chosen to be conservative, and can miss certain bugs.
config KCSAN_REPORT_RACE_UNKNOWN_ORIGIN
bool "Report races of unknown origin"
@@ -186,9 +184,17 @@ 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
@@ -197,6 +203,7 @@ 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
@@ -209,6 +216,7 @@ 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
@@ -224,4 +232,14 @@ config KCSAN_IGNORE_ATOMICS
due to two conflicting plain writes will be reported (aligned and
unaligned, if CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC=n).
+config KCSAN_PERMISSIVE
+ bool "Enable all additional permissive rules"
+ depends on KCSAN_REPORT_VALUE_CHANGE_ONLY
+ help
+ Enable additional permissive rules to ignore certain classes of data
+ races (also see kernel/kcsan/permissive.h). None of the permissive
+ rules imply that such data races are generally safe, but can be used
+ to further reduce reported data races due to data-racy patterns
+ common across the kernel.
+
endif # KCSAN