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+# SPDX-License-Identifier: GPL-2.0-only
+ bool
+ def_bool CC_IS_CLANG && $(cc-option,-fsanitize=thread -mllvm -tsan-distinguish-volatile=1)
+ help
+ For the list of compilers that support KCSAN, please see
+ <file:Documentation/dev-tools/kcsan.rst>.
+ depends on CC_IS_CLANG
+ depends on !$(cc-option,-Werror=unused-command-line-argument -fsanitize=thread -fsanitize-coverage=trace-pc)
+ help
+ Some versions of clang support either KCSAN and KCOV but not the
+ combination of the two.
+ See https://bugs.llvm.org/show_bug.cgi?id=45831 for the status
+ in newer releases.
+menuconfig KCSAN
+ bool "KCSAN: dynamic data race detector"
+ depends on DEBUG_KERNEL && !KASAN
+ depends on !KCSAN_KCOV_BROKEN
+ help
+ The Kernel Concurrency Sanitizer (KCSAN) is a dynamic
+ data-race detector that relies on compile-time instrumentation.
+ KCSAN uses a watchpoint-based sampling approach to detect races.
+ While KCSAN's primary purpose is to detect data races, it
+ also provides assertions to check data access constraints.
+ These assertions can expose bugs that do not manifest as
+ data races.
+ See <file:Documentation/dev-tools/kcsan.rst> for more details.
+ bool "Show verbose reports with more information about system state"
+ depends on PROVE_LOCKING
+ help
+ If enabled, reports show more information about the system state that
+ may help better analyze and debug races. This includes held locks and
+ IRQ trace events.
+ While this option should generally be benign, we call into more
+ external functions on report generation; if a race report is
+ generated from any one of them, system stability may suffer due to
+ deadlocks or recursion. If in doubt, say N.
+ bool "Debugging of KCSAN internals"
+ bool "Perform short selftests on boot"
+ default y
+ help
+ Run KCSAN selftests on boot. On test failure, causes the kernel to panic.
+ bool "Early enable during boot"
+ default y
+ help
+ If KCSAN should be enabled globally as soon as possible. KCSAN can
+ later be enabled/disabled via debugfs.
+ int "Number of available watchpoints"
+ default 64
+ help
+ Total number of available watchpoints. An address range maps into a
+ specific watchpoint slot as specified in kernel/kcsan/encoding.h.
+ Although larger number of watchpoints may not be usable due to
+ limited number of CPUs, a larger value helps to improve performance
+ due to reducing cache-line contention. The chosen default is a
+ conservative value; we should almost never observe "no_capacity"
+ events (see /sys/kernel/debug/kcsan).
+ int "Delay in microseconds (for tasks)"
+ default 80
+ help
+ For tasks, the microsecond delay after setting up a watchpoint.
+ int "Delay in microseconds (for interrupts)"
+ default 20
+ help
+ For interrupts, the microsecond delay after setting up a watchpoint.
+ Interrupts have tighter latency requirements, and their delay should
+ be lower than for tasks.
+ bool "Randomize above delays"
+ default y
+ help
+ If delays should be randomized, where the maximum is KCSAN_UDELAY_*.
+ If false, the chosen delays are always the KCSAN_UDELAY_* values
+ as defined above.
+ int "Skip instructions before setting up watchpoint"
+ default 4000
+ help
+ The number of per-CPU memory operations to skip, before another
+ watchpoint is set up, i.e. one in KCSAN_WATCH_SKIP per-CPU
+ memory operations are used to set up a watchpoint. A smaller value
+ results in more aggressive race detection, whereas a larger value
+ improves system performance at the cost of missing some races.
+ bool "Randomize watchpoint instruction skip count"
+ default y
+ help
+ If instruction skip count should be randomized, where the maximum is
+ KCSAN_WATCH_SKIP. If false, the chosen value is always
+ bool "Interruptible watchers"
+ help
+ If enabled, a task that set up a watchpoint may be interrupted while
+ delayed. This option will allow KCSAN to detect races between
+ interrupted tasks and other threads of execution on the same CPU.
+ Currently disabled by default, because not all safe per-CPU access
+ primitives and patterns may be accounted for, and therefore could
+ result in false positives.
+ int "Duration in milliseconds, in which any given race is only reported once"
+ default 3000
+ help
+ Any given race is only reported once in the defined time window.
+ Different races may still generate reports within a duration that is
+ smaller than the duration defined here. This allows rate limiting
+ 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.
+ bool "Report races of unknown origin"
+ default y
+ help
+ If KCSAN should report races where only one access is known, and the
+ conflicting access is of unknown origin. This type of race is
+ 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.
+ bool "Only report races where watcher observed a data value change"
+ default y
+ help
+ If enabled and a conflicting write is observed via a watchpoint, but
+ the data value of the memory location was observed to remain
+ unchanged, do not report the data race.
+ 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.
+ bool "Do not instrument marked atomic accesses"
+ help
+ Never instrument marked atomic accesses. This option can be used for
+ additional filtering. Conflicting marked atomic reads and plain
+ writes will never be reported as a data race, however, will cause
+ plain reads and marked writes to result in "unknown origin" reports.
+ races where at least one access is marked atomic will never be
+ reported.
+ Similar to KCSAN_ASSUME_PLAIN_WRITES_ATOMIC, but including unaligned
+ accesses, conflicting marked atomic reads and plain writes will not
+ be reported as data races; however, unlike that option, data races
+ due to two conflicting plain writes will be reported (aligned and
+endif # KCSAN

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