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Subject: Re: [PATCH] lib/stackdepot.c: use a non-instrumented version of
 memcpy()
References: <20180516153434.24479-1-glider@google.com>
From: Andrey Ryabinin <aryabinin@virtuozzo.com>
Message-ID: <f8a737c1-8cb9-15e1-2d98-454a4cafc1ed@virtuozzo.com>
Date: Wed, 16 May 2018 19:47:03 +0300
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Sender: owner-linux-mm@kvack.org
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To: Alexander Potapenko <glider@google.com>, akpm@linux-foundation.org, dvyukov@google.com
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org

On 05/16/2018 06:34 PM, Alexander Potapenko wrote:
> stackdepot used to call memcpy(), which compiler tools normally
> instrument, therefore every lookup used to unnecessarily call instrumented
> code.  This is somewhat ok in the case of KASAN, but under KMSAN a lot of
> time was spent in the instrumentation.
> 
> (A similar change has been previously committed for memcmp())
> 
> Signed-off-by: Alexander Potapenko <glider@google.com>
> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
> Cc: Dmitry Vyukov <dvyukov@google.com>
> ---
>  lib/stackdepot.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/lib/stackdepot.c b/lib/stackdepot.c
> index e513459a5601..d48c744fa750 100644
> --- a/lib/stackdepot.c
> +++ b/lib/stackdepot.c
> @@ -140,7 +140,7 @@ static struct stack_record *depot_alloc_stack(unsigned long *entries, int size,
>  	stack->handle.slabindex = depot_index;
>  	stack->handle.offset = depot_offset >> STACK_ALLOC_ALIGN;
>  	stack->handle.valid = 1;
> -	memcpy(stack->entries, entries, size * sizeof(unsigned long));
> +	__memcpy(stack->entries, entries, size * sizeof(unsigned long));

This has no effect. Since the whole file is not instrumented memcpy automagically replaced with __memcpy.