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The first version of Clang that supports -tsan-distinguish-volatile will
be able to support KCSAN. The first Clang release to do so, will be
Clang 11. This is due to satisfying all the following requirements:
1. Never emit calls to __tsan_func_{entry,exit}.
2. __no_kcsan functions should not call anything, not even
kcsan_{enable,disable}_current(), when using __{READ,WRITE}_ONCE => Requires
leaving them plain!
3. Support atomic_{read,set}*() with KCSAN, which rely on
arch_atomic_{read,set}*() using __{READ,WRITE}_ONCE() => Because of
#2, rely on Clang 11's -tsan-distinguish-volatile support. We will
double-instrument atomic_{read,set}*(), but that's reasonable given
it's still lower cost than the data_race() variant due to avoiding 2
extra calls (kcsan_{en,dis}able_current() calls).
4. __always_inline functions inlined into __no_kcsan functions are never
instrumented.
5. __always_inline functions inlined into instrumented functions are
instrumented.
6. __no_kcsan_or_inline functions may be inlined into __no_kcsan functions =>
Implies leaving 'noinline' off of __no_kcsan_or_inline.
7. Because of #6, __no_kcsan and __no_kcsan_or_inline functions should never be
spuriously inlined into instrumented functions, causing the accesses of the
__no_kcsan function to be instrumented.
Older versions of Clang do not satisfy #3. The latest GCC currently
doesn't support at least #1, #3, and #7.
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lkml.kernel.org/r/CANpmjNMTsY_8241bS7=XAfqvZHFLrVEkv_uM4aDUWE_kh3Rvbw@mail.gmail.com
Link: https://lkml.kernel.org/r/20200521142047.169334-7-elver@google.com
200 lines
7.5 KiB
Plaintext
200 lines
7.5 KiB
Plaintext
# SPDX-License-Identifier: GPL-2.0-only
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config HAVE_ARCH_KCSAN
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bool
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config HAVE_KCSAN_COMPILER
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def_bool CC_IS_CLANG && $(cc-option,-fsanitize=thread -mllvm -tsan-distinguish-volatile=1)
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help
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For the list of compilers that support KCSAN, please see
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<file:Documentation/dev-tools/kcsan.rst>.
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config KCSAN_KCOV_BROKEN
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def_bool KCOV && CC_HAS_SANCOV_TRACE_PC
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depends on CC_IS_CLANG
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depends on !$(cc-option,-Werror=unused-command-line-argument -fsanitize=thread -fsanitize-coverage=trace-pc)
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help
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Some versions of clang support either KCSAN and KCOV but not the
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combination of the two.
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See https://bugs.llvm.org/show_bug.cgi?id=45831 for the status
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in newer releases.
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menuconfig KCSAN
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bool "KCSAN: dynamic data race detector"
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depends on HAVE_ARCH_KCSAN && HAVE_KCSAN_COMPILER
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depends on DEBUG_KERNEL && !KASAN
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depends on !KCSAN_KCOV_BROKEN
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select STACKTRACE
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help
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The Kernel Concurrency Sanitizer (KCSAN) is a dynamic
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data-race detector that relies on compile-time instrumentation.
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KCSAN uses a watchpoint-based sampling approach to detect races.
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While KCSAN's primary purpose is to detect data races, it
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also provides assertions to check data access constraints.
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These assertions can expose bugs that do not manifest as
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data races.
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See <file:Documentation/dev-tools/kcsan.rst> for more details.
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if KCSAN
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config KCSAN_VERBOSE
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bool "Show verbose reports with more information about system state"
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depends on PROVE_LOCKING
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help
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If enabled, reports show more information about the system state that
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may help better analyze and debug races. This includes held locks and
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IRQ trace events.
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While this option should generally be benign, we call into more
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external functions on report generation; if a race report is
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generated from any one of them, system stability may suffer due to
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deadlocks or recursion. If in doubt, say N.
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config KCSAN_DEBUG
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bool "Debugging of KCSAN internals"
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config KCSAN_SELFTEST
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bool "Perform short selftests on boot"
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default y
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help
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Run KCSAN selftests on boot. On test failure, causes the kernel to panic.
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config KCSAN_EARLY_ENABLE
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bool "Early enable during boot"
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default y
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help
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If KCSAN should be enabled globally as soon as possible. KCSAN can
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later be enabled/disabled via debugfs.
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config KCSAN_NUM_WATCHPOINTS
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int "Number of available watchpoints"
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default 64
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help
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Total number of available watchpoints. An address range maps into a
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specific watchpoint slot as specified in kernel/kcsan/encoding.h.
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Although larger number of watchpoints may not be usable due to
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limited number of CPUs, a larger value helps to improve performance
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due to reducing cache-line contention. The chosen default is a
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conservative value; we should almost never observe "no_capacity"
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events (see /sys/kernel/debug/kcsan).
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config KCSAN_UDELAY_TASK
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int "Delay in microseconds (for tasks)"
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default 80
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help
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For tasks, the microsecond delay after setting up a watchpoint.
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config KCSAN_UDELAY_INTERRUPT
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int "Delay in microseconds (for interrupts)"
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default 20
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help
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For interrupts, the microsecond delay after setting up a watchpoint.
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Interrupts have tighter latency requirements, and their delay should
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be lower than for tasks.
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config KCSAN_DELAY_RANDOMIZE
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bool "Randomize above delays"
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default y
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help
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If delays should be randomized, where the maximum is KCSAN_UDELAY_*.
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If false, the chosen delays are always the KCSAN_UDELAY_* values
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as defined above.
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config KCSAN_SKIP_WATCH
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int "Skip instructions before setting up watchpoint"
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default 4000
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help
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The number of per-CPU memory operations to skip, before another
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watchpoint is set up, i.e. one in KCSAN_WATCH_SKIP per-CPU
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memory operations are used to set up a watchpoint. A smaller value
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results in more aggressive race detection, whereas a larger value
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improves system performance at the cost of missing some races.
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config KCSAN_SKIP_WATCH_RANDOMIZE
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bool "Randomize watchpoint instruction skip count"
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default y
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help
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If instruction skip count should be randomized, where the maximum is
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KCSAN_WATCH_SKIP. If false, the chosen value is always
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KCSAN_WATCH_SKIP.
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config KCSAN_INTERRUPT_WATCHER
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bool "Interruptible watchers"
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help
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If enabled, a task that set up a watchpoint may be interrupted while
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delayed. This option will allow KCSAN to detect races between
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interrupted tasks and other threads of execution on the same CPU.
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Currently disabled by default, because not all safe per-CPU access
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primitives and patterns may be accounted for, and therefore could
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result in false positives.
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config KCSAN_REPORT_ONCE_IN_MS
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int "Duration in milliseconds, in which any given race is only reported once"
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default 3000
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help
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Any given race is only reported once in the defined time window.
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Different races may still generate reports within a duration that is
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smaller than the duration defined here. This allows rate limiting
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reporting to avoid flooding the console with reports. Setting this
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to 0 disables rate limiting.
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# The main purpose of the below options is to control reported data races (e.g.
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# in fuzzer configs), and are not expected to be switched frequently by other
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# users. We could turn some of them into boot parameters, but given they should
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# not be switched normally, let's keep them here to simplify configuration.
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#
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# The defaults below are chosen to be very conservative, and may miss certain
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# bugs.
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config KCSAN_REPORT_RACE_UNKNOWN_ORIGIN
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bool "Report races of unknown origin"
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default y
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help
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If KCSAN should report races where only one access is known, and the
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conflicting access is of unknown origin. This type of race is
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reported if it was only possible to infer a race due to a data value
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change while an access is being delayed on a watchpoint.
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config KCSAN_REPORT_VALUE_CHANGE_ONLY
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bool "Only report races where watcher observed a data value change"
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default y
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help
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If enabled and a conflicting write is observed via a watchpoint, but
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the data value of the memory location was observed to remain
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unchanged, do not report the data race.
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config KCSAN_ASSUME_PLAIN_WRITES_ATOMIC
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bool "Assume that plain aligned writes up to word size are atomic"
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default y
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help
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Assume that plain aligned writes up to word size are atomic by
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default, and also not subject to other unsafe compiler optimizations
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resulting in data races. This will cause KCSAN to not report data
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races due to conflicts where the only plain accesses are aligned
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writes up to word size: conflicts between marked reads and plain
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aligned writes up to word size will not be reported as data races;
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notice that data races between two conflicting plain aligned writes
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will also not be reported.
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config KCSAN_IGNORE_ATOMICS
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bool "Do not instrument marked atomic accesses"
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help
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Never instrument marked atomic accesses. This option can be used for
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additional filtering. Conflicting marked atomic reads and plain
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writes will never be reported as a data race, however, will cause
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plain reads and marked writes to result in "unknown origin" reports.
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If combined with CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN=n, data
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races where at least one access is marked atomic will never be
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reported.
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Similar to KCSAN_ASSUME_PLAIN_WRITES_ATOMIC, but including unaligned
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accesses, conflicting marked atomic reads and plain writes will not
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be reported as data races; however, unlike that option, data races
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due to two conflicting plain writes will be reported (aligned and
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unaligned, if CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC=n).
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endif # KCSAN
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