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# SPDX-License-Identifier: GPL-2.0-only
config HAVE_ARCH_KCSAN
bool
menuconfig KCSAN
bool "KCSAN: watchpoint-based dynamic data race detector"
depends on HAVE_ARCH_KCSAN && !KASAN && STACKTRACE
help
Kernel Concurrency Sanitizer is a dynamic data race detector, which
uses a watchpoint-based sampling approach to detect races. See
<file:Documentation/dev-tools/kcsan.rst> for more details.
if KCSAN
config KCSAN_DEBUG
bool "Debugging of KCSAN internals"
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.
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_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.
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_WATCH_SKIP. If false, the chosen value is always
KCSAN_WATCH_SKIP.
config KCSAN_REPORT_ONCE_IN_MS
int "Duration in milliseconds, in which any given data race is only reported once"
default 3000
help
Any given data race is only reported once in the defined time window.
Different data 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.
# 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.
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_REPORT_VALUE_CHANGE_ONLY
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.
config KCSAN_IGNORE_ATOMICS
bool "Do not instrument marked atomic accesses"
help
If enabled, never instruments marked atomic accesses. This results in
not reporting data races where one access is atomic and the other is
a plain access.
endif # KCSAN
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