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SubjectRe: [PATCH] locking/atomic: simplify non-atomic wrappers
On Wed, 21 Jul 2021 at 17:58, Mark Rutland <mark.rutland@arm.com> wrote:
>
> Since the non-atomic arch_*() bitops use plain accesses, they are
> implicitly instrumnted by the compiler, and we work around this in the
> instrumented wrappers to avoid double instrumentation.
>
> It's simpler to avoid the wrappers entirely, and use the preprocessor to
> alias the arch_*() bitops to their regular versions, removing the need
> for checks in the instrumented wrappers.
>
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Suggested-by: Marco Elver <elver@google.com>
> Cc: Peter Zijlstra <peterz@infradead.org>

Reviewed-by: Marco Elver <elver@google.com>

Thank you!

> ---
> .../asm-generic/bitops/instrumented-non-atomic.h | 21 +++++++--------------
> include/asm-generic/bitops/non-atomic.h | 16 +++++++---------
> 2 files changed, 14 insertions(+), 23 deletions(-)
>
> Hi Peter,
>
> Are you happy to take this atop your queue/locking/core branch?
>
> This was suggested by Marco in [1], and also sidesteps some particularly bad
> stack spills as in [2].
>
> [1] https://lore.kernel.org/r/CANpmjNNVn4UxBCMg1ke9xaQNv52OMuQjr17GxUXojZKwiAFzzg@mail.gmail.com
> [2] https://lore.kernel.org/r/20210719100719.GB12806@C02TD0UTHF1T.local/
>
> Thanks,
> Mark.
>
> diff --git a/include/asm-generic/bitops/instrumented-non-atomic.h b/include/asm-generic/bitops/instrumented-non-atomic.h
> index e6c1540965d6..37363d570b9b 100644
> --- a/include/asm-generic/bitops/instrumented-non-atomic.h
> +++ b/include/asm-generic/bitops/instrumented-non-atomic.h
> @@ -24,8 +24,7 @@
> */
> static inline void __set_bit(long nr, volatile unsigned long *addr)
> {
> - if (!__is_defined(arch___set_bit_uses_plain_access))
> - instrument_write(addr + BIT_WORD(nr), sizeof(long));
> + instrument_write(addr + BIT_WORD(nr), sizeof(long));
> arch___set_bit(nr, addr);
> }
>
> @@ -40,8 +39,7 @@ static inline void __set_bit(long nr, volatile unsigned long *addr)
> */
> static inline void __clear_bit(long nr, volatile unsigned long *addr)
> {
> - if (!__is_defined(arch___clear_bit_uses_plain_access))
> - instrument_write(addr + BIT_WORD(nr), sizeof(long));
> + instrument_write(addr + BIT_WORD(nr), sizeof(long));
> arch___clear_bit(nr, addr);
> }
>
> @@ -56,8 +54,7 @@ static inline void __clear_bit(long nr, volatile unsigned long *addr)
> */
> static inline void __change_bit(long nr, volatile unsigned long *addr)
> {
> - if (!__is_defined(arch___change_bit_uses_plain_access))
> - instrument_write(addr + BIT_WORD(nr), sizeof(long));
> + instrument_write(addr + BIT_WORD(nr), sizeof(long));
> arch___change_bit(nr, addr);
> }
>
> @@ -95,8 +92,7 @@ static inline void __instrument_read_write_bitop(long nr, volatile unsigned long
> */
> static inline bool __test_and_set_bit(long nr, volatile unsigned long *addr)
> {
> - if (!__is_defined(arch___test_and_set_bit_uses_plain_access))
> - __instrument_read_write_bitop(nr, addr);
> + __instrument_read_write_bitop(nr, addr);
> return arch___test_and_set_bit(nr, addr);
> }
>
> @@ -110,8 +106,7 @@ static inline bool __test_and_set_bit(long nr, volatile unsigned long *addr)
> */
> static inline bool __test_and_clear_bit(long nr, volatile unsigned long *addr)
> {
> - if (!__is_defined(arch___test_and_clear_bit_uses_plain_access))
> - __instrument_read_write_bitop(nr, addr);
> + __instrument_read_write_bitop(nr, addr);
> return arch___test_and_clear_bit(nr, addr);
> }
>
> @@ -125,8 +120,7 @@ static inline bool __test_and_clear_bit(long nr, volatile unsigned long *addr)
> */
> static inline bool __test_and_change_bit(long nr, volatile unsigned long *addr)
> {
> - if (!__is_defined(arch___test_and_change_bit_uses_plain_access))
> - __instrument_read_write_bitop(nr, addr);
> + __instrument_read_write_bitop(nr, addr);
> return arch___test_and_change_bit(nr, addr);
> }
>
> @@ -137,8 +131,7 @@ static inline bool __test_and_change_bit(long nr, volatile unsigned long *addr)
> */
> static inline bool test_bit(long nr, const volatile unsigned long *addr)
> {
> - if (!__is_defined(arch_test_bit_uses_plain_access))
> - instrument_atomic_read(addr + BIT_WORD(nr), sizeof(long));
> + instrument_atomic_read(addr + BIT_WORD(nr), sizeof(long));
> return arch_test_bit(nr, addr);
> }
>
> diff --git a/include/asm-generic/bitops/non-atomic.h b/include/asm-generic/bitops/non-atomic.h
> index c8149cd52730..365377fb104b 100644
> --- a/include/asm-generic/bitops/non-atomic.h
> +++ b/include/asm-generic/bitops/non-atomic.h
> @@ -21,7 +21,7 @@ arch___set_bit(int nr, volatile unsigned long *addr)
>
> *p |= mask;
> }
> -#define arch___set_bit_uses_plain_access
> +#define __set_bit arch___set_bit
>
> static __always_inline void
> arch___clear_bit(int nr, volatile unsigned long *addr)
> @@ -31,7 +31,7 @@ arch___clear_bit(int nr, volatile unsigned long *addr)
>
> *p &= ~mask;
> }
> -#define arch___clear_bit_uses_plain_access
> +#define __clear_bit arch___clear_bit
>
> /**
> * arch___change_bit - Toggle a bit in memory
> @@ -50,7 +50,7 @@ void arch___change_bit(int nr, volatile unsigned long *addr)
>
> *p ^= mask;
> }
> -#define arch___change_bit_uses_plain_access
> +#define __change_bit arch___change_bit
>
> /**
> * arch___test_and_set_bit - Set a bit and return its old value
> @@ -71,7 +71,7 @@ arch___test_and_set_bit(int nr, volatile unsigned long *addr)
> *p = old | mask;
> return (old & mask) != 0;
> }
> -#define arch___test_and_set_bit_uses_plain_access
> +#define __test_and_set_bit arch___test_and_set_bit
>
> /**
> * arch___test_and_clear_bit - Clear a bit and return its old value
> @@ -92,7 +92,7 @@ arch___test_and_clear_bit(int nr, volatile unsigned long *addr)
> *p = old & ~mask;
> return (old & mask) != 0;
> }
> -#define arch___test_and_clear_bit_uses_plain_access
> +#define __test_and_clear_bit arch___test_and_clear_bit
>
> /* WARNING: non atomic and it can be reordered! */
> static __always_inline int
> @@ -105,7 +105,7 @@ arch___test_and_change_bit(int nr, volatile unsigned long *addr)
> *p = old ^ mask;
> return (old & mask) != 0;
> }
> -#define arch___test_and_change_bit_uses_plain_access
> +#define __test_and_change_bit arch___test_and_change_bit
>
> /**
> * arch_test_bit - Determine whether a bit is set
> @@ -117,8 +117,6 @@ arch_test_bit(int nr, const volatile unsigned long *addr)
> {
> return 1UL & (addr[BIT_WORD(nr)] >> (nr & (BITS_PER_LONG-1)));
> }
> -#define arch_test_bit_uses_plain_access
> -
> -#include <asm-generic/bitops/instrumented-non-atomic.h>
> +#define test_bit arch_test_bit
>
> #endif /* _ASM_GENERIC_BITOPS_NON_ATOMIC_H_ */
> --
> 2.11.0
>

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