kernel/include/asm-generic/bitops/instrumented-non-atomic.h, branch linux-5.17.y

bitops, kcsan: Partially revert instrumentation for non-atomic bitops

2020-08-24T22:10:24Z

Previous to the change to distinguish read-write accesses, when CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC=y is set, KCSAN would consider the non-atomic bitops as atomic. We want to partially revert to this behaviour, but with one important distinction: report racing modifications, since lost bits due to non-atomicity are certainly possible. Given the operations here only modify a single bit, assuming non-atomicity of the writer is sufficient may be reasonable for certain usage (and follows the permissible nature of the "assume plain writes atomic" rule). In other words: 1. We want non-atomic read-modify-write races to be reported; this is accomplished by kcsan_check_read(), where any concurrent write (atomic or not) will generate a report. 2. We do not want to report races with marked readers, but -do- want to report races with unmarked readers; this is accomplished by the instrument_write() ("assume atomic write" with Kconfig option set). With the above rules, when KCSAN_ASSUME_PLAIN_WRITES_ATOMIC is selected, it is hoped that KCSAN's reporting behaviour is better aligned with current expected permissible usage for non-atomic bitops. Note that, a side-effect of not telling KCSAN that the accesses are read-writes, is that this information is not displayed in the access summary in the report. It is, however, visible in inline-expanded stack traces. For now, it does not make sense to introduce yet another special case to KCSAN's runtime, only to cater to the case here. Cc: Dmitry Vyukov Cc: Paul E. McKenney Cc: Will Deacon Cc: Arnd Bergmann Cc: Daniel Axtens Cc: Michael Ellerman Cc: Signed-off-by: Marco Elver Signed-off-by: Paul E. McKenney

asm-generic/bitops: Use instrument_read_write() where appropriate

2020-08-24T22:09:59Z

Use the new instrument_read_write() where appropriate. Acked-by: Peter Zijlstra (Intel) Signed-off-by: Marco Elver Signed-off-by: Paul E. McKenney

asm-generic, kcsan: Add KCSAN instrumentation for bitops

2020-03-21T08:41:46Z

Add explicit KCSAN checks for bitops. Acked-by: Arnd Bergmann Signed-off-by: Marco Elver Signed-off-by: Paul E. McKenney Signed-off-by: Ingo Molnar

kasan: support instrumented bitops combined with generic bitops

2019-11-07T02:15:39Z

Currently bitops-instrumented.h assumes that the architecture provides atomic, non-atomic and locking bitops (e.g. both set_bit and __set_bit). This is true on x86 and s390, but is not always true: there is a generic bitops/non-atomic.h header that provides generic non-atomic operations, and also a generic bitops/lock.h for locking operations. powerpc uses the generic non-atomic version, so it does not have it's own e.g. __set_bit that could be renamed arch___set_bit. Split up bitops-instrumented.h to mirror the atomic/non-atomic/lock split. This allows arches to only include the headers where they have arch-specific versions to rename. Update x86 and s390. (The generic operations are automatically instrumented because they're written in C, not asm.) Suggested-by: Christophe Leroy Reviewed-by: Christophe Leroy Signed-off-by: Daniel Axtens Acked-by: Marco Elver Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20190820024941.12640-1-dja@axtens.net