Re: [PATCH net-next v3 2/5] bitops: add non-atomic bitops for pointers

Toke Høiland-Jørgensen
2021-06-22T22:00:36Z

Kumar Kartikeya Dwivedi <memxor@gmail.com> writes:

> cpumap needs to set, clear, and test the lowest bit in skb pointer in
> various places. To make these checks less noisy, add pointer friendly
> bitop macros that also do some typechecking to sanitize the argument.
>
> These wrap the non-atomic bitops __set_bit, __clear_bit, and test_bit
> but for pointer arguments. Pointer's address has to be passed in and it
> is treated as an unsigned long *, since width and representation of
> pointer and unsigned long match on targets Linux supports. They are
> prefixed with double underscore to indicate lack of atomicity.
>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> ---
> include/linux/bitops.h | 19 +++++++++++++++++++
> include/linux/typecheck.h | 10 ++++++++++
> 2 files changed, 29 insertions(+)
>
> diff --git a/include/linux/bitops.h b/include/linux/bitops.h
> index 26bf15e6cd35..a9e336b9fa4d 100644
> --- a/include/linux/bitops.h
> +++ b/include/linux/bitops.h
> @@ -4,6 +4,7 @@
>
> #include <asm/types.h>
> #include <linux/bits.h>
> +#include <linux/typecheck.h>
>
> #include <uapi/linux/kernel.h>
>
> @@ -253,6 +254,24 @@ static __always_inline void __assign_bit(long nr, volatile unsigned long *addr,
> __clear_bit(nr, addr);
> }
>
> +#define __ptr_set_bit(nr, addr) \
> + ({ \
> + typecheck_pointer(*(addr)); \
> + __set_bit(nr, (unsigned long *)(addr)); \
> + })
> +
> +#define __ptr_clear_bit(nr, addr) \
> + ({ \
> + typecheck_pointer(*(addr)); \
> + __clear_bit(nr, (unsigned long *)(addr)); \
> + })
> +
> +#define __ptr_test_bit(nr, addr) \
> + ({ \
> + typecheck_pointer(*(addr)); \
> + test_bit(nr, (unsigned long *)(addr)); \
> + })
> +

Before these were functions that returned the modified values, now they
are macros that modify in-place. Why the change? :)

-Toke