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Date:   Fri, 28 Aug 2020 22:27:25 +0200
From:   Daniel Borkmann <>
To:     Alexei Starovoitov <>,
Subject: Re: [PATCH v3 bpf-next 1/5] mm/error_inject: Fix allow_error_inject
 function signatures.

On 8/28/20 12:01 AM, Alexei Starovoitov wrote:
> From: Alexei Starovoitov <>
> 'static' and 'static noinline' function attributes make no guarantees that
> gcc/clang won't optimize them. The compiler may decide to inline 'static'
> function and in such case ALLOW_ERROR_INJECT becomes meaningless. The compiler
> could have inlined __add_to_page_cache_locked() in one callsite and didn't
> inline in another. In such case injecting errors into it would cause
> unpredictable behavior. It's worse with 'static noinline' which won't be
> inlined, but it still can be optimized. Like the compiler may decide to remove
> one argument or constant propagate the value depending on the callsite.
> To avoid such issues make sure that these functions are global noinline.

Back in the days when adding 6bf37e5aa90f ("crypto: crypto_memneq - add equality
testing of memory regions w/o timing leaks") we added noinline, but also an
explicit EXPORT_SYMBOL() to prevent this from being optimized away; I wonder
whether ALLOW_ERROR_INJECT() should have something implicit here too to prevent
from optimization .. otoh we probably don't want to expose every ALLOW_ERROR_INJECT()
function also to modules generically...


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