wait_on_bit: add an acquire memory barrier

There are several places in the kernel where wait_on_bit is not followed
by a memory barrier (for example, in drivers/md/dm-bufio.c:new_read).

On architec

wait_on_bit: add an acquire memory barrier

There are several places in the kernel where wait_on_bit is not followed
by a memory barrier (for example, in drivers/md/dm-bufio.c:new_read).

On architectures with weak memory ordering, it may happen that memory
accesses that follow wait_on_bit are reordered before wait_on_bit and
they may return invalid data.

Fix this class of bugs by introducing a new function "test_bit_acquire"
that works like test_bit, but has acquire memory ordering semantics.

Signed-off-by: Mikulas Patocka <[email protected]>
Acked-by: Will Deacon <[email protected]>
Cc: [email protected]
Signed-off-by: Linus Torvalds <[email protected]>

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bitops: define const_*() versions of the non-atomics

Define const_*() variants of the non-atomic bitops to be used when
the input arguments are compile-time constants, so that the compiler
will be a

bitops: define const_*() versions of the non-atomics

Define const_*() variants of the non-atomic bitops to be used when
the input arguments are compile-time constants, so that the compiler
will be always able to resolve those to compile-time constants as
well. Those are mostly direct aliases for generic_*() with one
exception for const_test_bit(): the original one is declared
atomic-safe and thus doesn't discard the `volatile` qualifier, so
in order to let optimize code, define it separately disregarding
the qualifier.
Add them to the compile-time type checks as well just in case.

Suggested-by: Marco Elver <[email protected]>
Signed-off-by: Alexander Lobakin <[email protected]>
Reviewed-by: Marco Elver <[email protected]>
Reviewed-by: Andy Shevchenko <[email protected]>
Signed-off-by: Yury Norov <[email protected]>

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bitops: unify non-atomic bitops prototypes across architectures

Currently, there is a mess with the prototypes of the non-atomic
bitops across the different architectures:

ret bool, int, unsigned l

bitops: unify non-atomic bitops prototypes across architectures

Currently, there is a mess with the prototypes of the non-atomic
bitops across the different architectures:

ret bool, int, unsigned long
nr int, long, unsigned int, unsigned long
addr volatile unsigned long *, volatile void *

Thankfully, it doesn't provoke any bugs, but can sometimes make
the compiler angry when it's not handy at all.
Adjust all the prototypes to the following standard:

ret bool retval can be only 0 or 1
nr unsigned long native; signed makes no sense
addr volatile unsigned long * bitmaps are arrays of ulongs

Next, some architectures don't define 'arch_' versions as they don't
support instrumentation, others do. To make sure there is always the
same set of callables present and to ease any potential future
changes, make them all follow the rule:
* architecture-specific files define only 'arch_' versions;
* non-prefixed versions can be defined only in asm-generic files;
and place the non-prefixed definitions into a new file in
asm-generic to be included by non-instrumented architectures.

Finally, add some static assertions in order to prevent people from
making a mess in this room again.
I also used the %__always_inline attribute consistently, so that
they always get resolved to the actual operations.

Suggested-by: Andy Shevchenko <[email protected]>
Signed-off-by: Alexander Lobakin <[email protected]>
Acked-by: Mark Rutland <[email protected]>
Reviewed-by: Yury Norov <[email protected]>
Reviewed-by: Andy Shevchenko <[email protected]>
Signed-off-by: Yury Norov <[email protected]>

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bitops: always define asm-generic non-atomic bitops

Move generic non-atomic bitops from the asm-generic header which
gets included only when there are no architecture-specific
alternatives, to a sep

bitops: always define asm-generic non-atomic bitops

Move generic non-atomic bitops from the asm-generic header which
gets included only when there are no architecture-specific
alternatives, to a separate independent file to make them always
available.
Almost no actual code changes, only one comment added to
generic_test_bit() saying that it's an atomic operation itself
and thus `volatile` must always stay there with no cast-aways.

Suggested-by: Andy Shevchenko <[email protected]> # comment
Suggested-by: Marco Elver <[email protected]> # reference to kernel-doc
Signed-off-by: Alexander Lobakin <[email protected]>
Reviewed-by: Andy Shevchenko <[email protected]>
Reviewed-by: Marco Elver <[email protected]>
Signed-off-by: Yury Norov <[email protected]>

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