linux-kernel - Re: [PATCH] kcsan: fix section mismatch for __write_once_size/blacklisted

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Date:   Tue, 5 May 2020 16:17:33 +0200
From:   Marco Elver <elver@...gle.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Kees Cook <keescook@...omium.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Alexander Potapenko <glider@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux@...glegroups.com, Will Deacon <will@...nel.org>
Subject: Re: [PATCH] kcsan: fix section mismatch for __write_once_size/blacklisted_initcalls

On Tue, 5 May 2020 at 16:11, Arnd Bergmann <arnd@...db.de> wrote:
>
> Moving __write_once_size out of line causes a section mismatch warning
> with clang in one instance:
>
> WARNING: modpost: vmlinux.o(.text+0x8dc): Section mismatch in reference from the function __write_once_size() to the variable .init.data:blacklisted_initcalls
> The function __write_once_size() references
> the variable __initdata blacklisted_initcalls.
> This is often because __write_once_size lacks a __initdata
> annotation or the annotation of blacklisted_initcalls is wrong.
>
> Remove the __init_or_module annotation from the variable as a workaround.
>
> Fixes: dfd402a4c4ba ("kcsan: Add Kernel Concurrency Sanitizer infrastructure")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
> So far, my randconfig checks found two such instances, one for read_once
> and one for write_once. There are probably a couple more in random
> configurations, but I guess they are rare enough that we can just work
> around them like this.

[+Cc Will]

Thanks for testing and fixing this. Note that this may no longer be
necessary once Will's patches land. Also noted here:
https://lkml.kernel.org/r/CANpmjNNw6M9Gqj6WGTHH4Cegu8roTVu5x6Vqs_tCBxX3gPwL4A@mail.gmail.com

For reference, Will's series:
https://lore.kernel.org/lkml/20200421151537.19241-1-will@kernel.org/

Thanks,
-- Marco


> ---
>  init/main.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/init/main.c b/init/main.c
> index 8f78399697e3..441c384a73cd 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -1020,7 +1020,7 @@ struct blacklist_entry {
>         char *buf;
>  };
>
> -static __initdata_or_module LIST_HEAD(blacklisted_initcalls);
> +static LIST_HEAD(blacklisted_initcalls);
>
>  static int __init initcall_blacklist(char *str)
>  {
> --
> 2.26.0
>