Re: [PATCH v3 7/7] asm-generic, x86: add comments for atomic instrumentation

[Andrey Ryabinin]

On 06/06/2017 01:11 PM, Dmitry Vyukov wrote:
> The comments are factored out from the code changes to make them
> easier to read. Add them separately to explain some non-obvious
> aspects.
> 
> Signed-off-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Will Deacon <will.deacon@xxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: kasan-dev@xxxxxxxxxxxxxxxx
> Cc: linux-mm@xxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: x86@xxxxxxxxxx
> ---
>  arch/x86/include/asm/atomic.h             |  7 +++++++
>  include/asm-generic/atomic-instrumented.h | 30 ++++++++++++++++++++++++++++++
>  2 files changed, 37 insertions(+)
> 
> diff --git a/arch/x86/include/asm/atomic.h b/arch/x86/include/asm/atomic.h
> index b7900346c77e..8a9e65e585db 100644
> --- a/arch/x86/include/asm/atomic.h
> +++ b/arch/x86/include/asm/atomic.h
> @@ -23,6 +23,13 @@
>   */
>  static __always_inline int arch_atomic_read(const atomic_t *v)
>  {
> +	/*
> +	 * Note: READ_ONCE() here leads to double instrumentation as
> +	 * both READ_ONCE() and atomic_read() contain instrumentation.
> +	 * This is a deliberate choice. READ_ONCE_NOCHECK() is compiled to a
> +	 * non-inlined function call that considerably increases binary size
> +	 * and stack usage under KASAN.
> +	 */


Not sure that this worth commenting. Whoever is looking into arch_atomic_read() internals
probably don't even think about KASAN instrumentation, so I'd remove this comment.


>  	return READ_ONCE((v)->counter);
>  }
>