netdev - Re: [PATCH v3 bpf-next 1/5] mm/error_inject: Fix allow_error

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Message-ID: <9a4b6133-e0ca-c34e-6f85-1f04039109d5@toxicpanda.com>
Date:   Thu, 27 Aug 2020 19:58:57 -0400
From:   Josef Bacik <josef@...icpanda.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        davem@...emloft.net
Cc:     daniel@...earbox.net, bpoirier@...e.com, akpm@...ux-foundation.org,
        hannes@...xchg.org, netdev@...r.kernel.org, bpf@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH v3 bpf-next 1/5] mm/error_inject: Fix allow_error_inject
 function signatures.

On 8/27/20 6:01 PM, Alexei Starovoitov wrote:
> From: Alexei Starovoitov <ast@...nel.org>
> 
> '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.
> 
> Fixes: af3b854492f3 ("mm/page_alloc.c: allow error injection")
> Fixes: cfcbfb1382db ("mm/filemap.c: enable error injection at add_to_page_cache()")
> Signed-off-by: Alexei Starovoitov <ast@...nel.org>

Reviewed-by: Josef Bacik <josef@...icpanda.com>

Thanks,

Josef