Re: [PATCH 2/3] asm-generic, x86: wrap atomic operations

Andrey Ryabinin
2017-03-20T16:56:23Z

On 03/14/2017 10:24 PM, Dmitry Vyukov wrote:

> diff --git a/arch/x86/include/asm/atomic.h b/arch/x86/include/asm/atomic.h
> index 14635c5ea025..95dd167eb3af 100644
> --- a/arch/x86/include/asm/atomic.h
> +++ b/arch/x86/include/asm/atomic.h
> @@ -16,36 +16,46 @@
> #define ATOMIC_INIT(i) { (i) }
>
> /**
> - * atomic_read - read atomic variable
> + * arch_atomic_read - read atomic variable
> * @v: pointer of type atomic_t
> *
> * Atomically reads the value of @v.
> */
> -static __always_inline int atomic_read(const atomic_t *v)
> +static __always_inline int arch_atomic_read(const atomic_t *v)
> {
> - return READ_ONCE((v)->counter);
> + /*
> + * We use READ_ONCE_NOCHECK() because atomic_read() contains KASAN
> + * instrumentation. Double instrumentation is unnecessary.
> + */
> + return READ_ONCE_NOCHECK((v)->counter);

This is kinda questionable "optimization". READ_ONCE_NOCHECK() is actually
function call to __read_once_size_nocheck().
So this _NOCHECK adds some bloat to the kernel.
E.g. on my .config remove of _NOCHECK() saves ~400K of .text:

size vmlinux_read
text data bss dec hex filename
40548235 16418838 23289856 80256929 4c89fa1 vmlinux_read
size vmlinux_read_nocheck
text data bss dec hex filename
40938418 16451958 23289856 80680232 4cf1528 vmlinux_read_nocheck