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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Message-ID: <alpine.LFD.2.22.394.2006012259520.4793@earth2.lan>
Date:   Mon, 1 Jun 2020 23:01:15 +0100 (BST)
From:   "ý" <jbi.octave@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
cc:     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 Mon, 1 Jun 2020, 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
>> 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
>
>
>
Thanks for the feedback, I take good note.
Jules