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:   Fri, 5 Jun 2020 08:42:35 +0100 (BST)
From:   "ý" <jbi.octave@...il.com>
To:     Luc Van Oostenryck <luc.vanoostenryck@...il.com>
cc:     Steven Rostedt <rostedt@...dmis.org>,
        Jules Irenge <jbi.octave@...il.com>,
        linux-kernel@...r.kernel.org, tglx@...utronix.de,
        paulmck@...nel.org, mingo@...hat.com, boqun.feng@...il.com,
        Borislav Petkov <bp@...en8.de>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "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 Wed, 3 Jun 2020, Luc Van Oostenryck wrote:

> On Mon, Jun 01, 2020 at 03:46:47PM -0400, Steven Rostedt wrote:
>> 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
>
> Yes.
>
>> 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.
>
> The annotations added by commit
>  074376ac0e1d ("ftrace/x86: Anotate text_mutex split between ...
> are indeed wrong (because they don't match what the functions are
> really doing / mutex operations have never been annotated).
> The're also pointless since their prototypes are un-annotated.

Interesting, I would think the best way would then be to remove the 
annotations. There are quite a number of them.

I will have to investigate more on mutex and annotation before moving 
forward.

Thanks for feedback.

Jules