linux-kernel - Re: [PATCH 4/5] x86/ftrace: Add annotations for ftrace_arch_code_modify_prepare() and ftrace_arch_code_modify_post

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Date:   Mon, 1 Jun 2020 15:46:47 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Jules Irenge <jbi.octave@...il.com>
Cc:     linux-kernel@...r.kernel.org, tglx@...utronix.de,
        paulmck@...nel.org, mingo@...hat.com, boqun.feng@...il.com,
        Borislav Petkov <bp@...en8.de>,
        x86@...nel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)),
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 4/5] x86/ftrace: Add annotations for
 ftrace_arch_code_modify_prepare() and
 ftrace_arch_code_modify_post_process()

On Mon,  1 Jun 2020 19:45:51 +0100
Jules Irenge <jbi.octave@...il.com> wrote:

> Sparse reports warnings
> 
> warning: context imbalance in ftrace_arch_code_modify_prepare()
> 	- wrong count at exit
> warning: context imbalance in ftrace_arch_code_modify_post_process()
> 	- wrong count at exit
> 
> The root cause is that even if
>  the annotations on the function are correct,
> mutex do not support annotation
> This makes Sparse to complain.
> To fix this,
> __acquire(&text_mutex) and
>  __release(&text_mutex) annotations are added
> inside ftrace_arch_code_modify_prepare()
> and ftrace_arch_code_modify_post_process()
> respectively.

Wait what? This looks like either a bug in sparse, or we just remove the
annotations. This just makes the code ugly, and looks silly.

Nack!

-- Steve


> 
> Signed-off-by: Jules Irenge <jbi.octave@...il.com>
> ---
>  arch/x86/kernel/ftrace.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
> index 37a0aeaf89e7..737c07ab2e07 100644
> --- a/arch/x86/kernel/ftrace.c
> +++ b/arch/x86/kernel/ftrace.c
> @@ -46,6 +46,7 @@ int ftrace_arch_code_modify_prepare(void)
>  	 * ftrace has it set to "read/write".
>  	 */
>  	mutex_lock(&text_mutex);
> +	__acquire(&text_mutex);
>  	ftrace_poke_late = 1;
>  	return 0;
>  }
> @@ -61,6 +62,7 @@ int ftrace_arch_code_modify_post_process(void)
>  	text_poke_finish();
>  	ftrace_poke_late = 0;
>  	mutex_unlock(&text_mutex);
> +	__release(&text_mutex);
>  	return 0;
>  }
>