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# SPDX-License-Identifier: GPL-2.0-only config HAVE_ARCH_KCSAN bool config HAVE_KCSAN_COMPILER def_bool (CC_IS_CLANG && $(cc-option,-fsanitize=thread -mllvm -tsan-distinguish-volatile=1)) || \ (CC_IS_GCC && $(cc-option,-fsanitize=thread --param tsan-distinguish-volatile=1)) help For the list of compilers that support KCSAN, please see <file:Documentation/dev-tools/kcsan.rst>. menuconfig KCSAN bool "KCSAN: dynamic data race detector" depends on HAVE_ARCH_KCSAN && HAVE_KCSAN_COMPILER depends on DEBUG_KERNEL && !KASAN select CONSTRUCTORS select STACKTRACE 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. if KCSAN 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" 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. config KCSAN_SELFTEST bool "Perform short selftests on boot" default y help Run KCSAN selftests on boot. On test failure, causes the kernel to panic. Recommended to be enabled, ensuring critical functionality works as intended. config KCSAN_KUNIT_TEST tristate "KCSAN test for integrated runtime behaviour" if !KUNIT_ALL_TESTS default KUNIT_ALL_TESTS depends on TRACEPOINTS && KUNIT select TORTURE_TEST help KCSAN test focusing on behaviour of the integrated runtime. Tests various race scenarios, and verifies the reports generated to console. Makes use of KUnit for test organization, and the Torture framework for test thread control. Each test case may run at least up to KCSAN_REPORT_ONCE_IN_MS milliseconds. Test run duration may be optimized by building the kernel and KCSAN test with KCSAN_REPORT_ONCE_IN_MS set to a lower than default value. Say Y here if you want the test to be built into the kernel and run during boot; say M if you want the test to build as a module; say N if you are unsure. config KCSAN_EARLY_ENABLE 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. config KCSAN_NUM_WATCHPOINTS 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). config KCSAN_UDELAY_TASK int "Delay in microseconds (for tasks)" default 80 help For tasks, the microsecond delay after setting up a watchpoint. config KCSAN_UDELAY_INTERRUPT 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. config KCSAN_DELAY_RANDOMIZE 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. config KCSAN_SKIP_WATCH 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_SKIP_WATCH 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. config KCSAN_SKIP_WATCH_RANDOMIZE bool "Randomize watchpoint instruction skip count" default y help If instruction skip count should be randomized, where the maximum is KCSAN_SKIP_WATCH. If false, the chosen value is always KCSAN_SKIP_WATCH. config KCSAN_INTERRUPT_WATCHER 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 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. config KCSAN_REPORT_ONCE_IN_MS 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, 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" 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. 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_WEAK_MEMORY bool "Enable weak memory modeling to detect missing memory barriers" default y depends on KCSAN_STRICT help Enable support for modeling a subset of weak memory, which allows detecting a subset of data races due to missing memory barriers. Depends on KCSAN_STRICT, because the options strengthening certain plain accesses by default (depending on !KCSAN_STRICT) reduce the ability to detect any data races invoving reordered accesses, in particular reordered writes. Weak memory modeling relies on additional instrumentation and may affect performance. 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 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 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 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" depends on !KCSAN_STRICT 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. If combined with CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN=n, data 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 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