linux-stable/include/asm-generic/bitops
Marco Elver 068df05363 bitops, kcsan: Partially revert instrumentation for non-atomic bitops
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 <dvyukov@google.com>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Will Deacon <will@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Daniel Axtens <dja@axtens.net>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: <linux-arch@vger.kernel.org>
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-08-24 15:10:24 -07:00
..
__ffs.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
__fls.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
arch_hweight.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
atomic.h locking/atomics, asm-generic/bitops/atomic.h: Rewrite using atomic_*() APIs 2018-06-21 12:52:11 +02:00
builtin-__ffs.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
builtin-__fls.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
builtin-ffs.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
builtin-fls.h fls: change parameter to unsigned int 2019-01-04 13:13:46 -08:00
const_hweight.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
ext2-atomic-setbit.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
ext2-atomic.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
ffs.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
ffz.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
find.h bitops: introduce the for_each_set_clump8 macro 2019-12-04 19:44:12 -08:00
fls.h fls: change parameter to unsigned int 2019-01-04 13:13:46 -08:00
fls64.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
hweight.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
instrumented-atomic.h asm-generic/bitops: Use instrument_read_write() where appropriate 2020-08-24 15:09:59 -07:00
instrumented-lock.h asm-generic/bitops: Use instrument_read_write() where appropriate 2020-08-24 15:09:59 -07:00
instrumented-non-atomic.h bitops, kcsan: Partially revert instrumentation for non-atomic bitops 2020-08-24 15:10:24 -07:00
le.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
lock.h locking/atomics, asm-generic/bitops/lock.h: Rewrite using atomic_fetch_*() 2018-06-21 12:52:12 +02:00
non-atomic.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
sched.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00