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# SPDX-License-Identifier: GPL-2.0-only
config HAVE_ARCH_KCSAN
bool
menuconfig KCSAN
bool "KCSAN: dynamic data race detector"
depends on HAVE_ARCH_KCSAN && DEBUG_KERNEL && !KASAN
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 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_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_INTERRUPT_WATCHER
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.
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 (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"
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_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
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).
endif # KCSAN
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