Hector Martin 1b7e0482ab locking/atomic: Make test_and_*_bit() ordered on failure ... commit 415d832497 upstream. These operations are documented as always ordered in include/asm-generic/bitops/instrumented-atomic.h, and producer-consumer type use cases where one side needs to ensure a flag is left pending after some shared data was updated rely on this ordering, even in the failure case. This is the case with the workqueue code, which currently suffers from a reproducible ordering violation on Apple M1 platforms (which are notoriously out-of-order) that ends up causing the TTY layer to fail to deliver data to userspace properly under the right conditions. This change fixes that bug. Change the documentation to restrict the "no order on failure" story to the _lock() variant (for which it makes sense), and remove the early-exit from the generic implementation, which is what causes the missing barrier semantics in that case. Without this, the remaining atomic op is fully ordered (including on ARM64 LSE, as of recent versions of the architecture spec). Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: stable@vger.kernel.org Fixes: e986a0d6cb ("locking/atomics, asm-generic/bitops/atomic.h: Rewrite using atomic_*() APIs") Fixes: 61e02392d3 ("locking/atomic/bitops: Document and clarify ordering semantics for failed test_and_{}_bit()") Signed-off-by: Hector Martin <marcan@marcan.st> Acked-by: Will Deacon <will@kernel.org> Reviewed-by: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>		2022-08-25 11:39:54 +02:00
..
__ffs.h
__fls.h
arch_hweight.h
atomic.h	locking/atomic: Make test_and_*_bit() ordered on failure	2022-08-25 11:39:54 +02:00
builtin-__ffs.h
builtin-__fls.h
builtin-ffs.h	asm-generic: ffs: Drop bogus reference to ffz location	2021-08-11 11:38:10 +02:00
builtin-fls.h	fls: change parameter to unsigned int	2019-01-04 13:13:46 -08:00
const_hweight.h
ext2-atomic-setbit.h
ext2-atomic.h
ffs.h	asm-generic: ffs: Drop bogus reference to ffz location	2021-08-11 11:38:10 +02:00
ffz.h
find.h	bitops: protect find_first_{,zero}_bit properly	2022-01-27 11:05:34 +01:00
fls.h	fls: change parameter to unsigned int	2019-01-04 13:13:46 -08:00
fls64.h
hweight.h
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	locking/atomic: simplify non-atomic wrappers	2021-08-04 15:16:47 +02:00
le.h	lib: add fast path for find_next_*_bit()	2021-05-06 19:24:12 -07:00
lock.h	locking/atomic: add generic arch_*() bitops	2021-07-16 18:46:45 +02:00
non-atomic.h	asm-generic changes for 5.15	2021-09-01 15:13:02 -07:00
sched.h