linux-kernel - Re: [PATCH v3] x86/resctrl: Annotate get_mem_config() functions as _

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Message-ID: <20240920093722.GA411564@thelio-3990X>
Date: Fri, 20 Sep 2024 02:37:22 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Reinette Chatre <reinette.chatre@...el.com>
Cc: Fenghua Yu <fenghua.yu@...el.com>, x86@...nel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
	patches@...ts.linux.dev
Subject: Re: [PATCH v3] x86/resctrl: Annotate get_mem_config() functions as
 __init

On Thu, Sep 19, 2024 at 02:15:34PM -0700, Reinette Chatre wrote:
> 
> 
> On 9/17/24 9:02 AM, Nathan Chancellor wrote:
> > After a recent LLVM change [1] that deduces __cold on functions that
> > only call cold code (such as __init functions), there is a section
> > mismatch warning from __get_mem_config_intel(), which got moved to
> > .text.unlikely. as a result of that optimization:
> > 
> >   WARNING: modpost: vmlinux: section mismatch in reference: __get_mem_config_intel+0x77 (section: .text.unlikely.) -> thread_throttle_mode_init (section: .init.text)
> > 
> > Mark __get_mem_config_intel() as __init as well since it is only called
> > from __init code, which clears up the warning.
> > 
> > While __rdt_get_mem_config_amd() does not exhibit a warning because it
> > does not call any __init code, it is a similar function that is only
> > called from __init code like __get_mem_config_intel(), so mark it __init
> > as well to keep the code symmetrical.
> > 
> > Link: https://github.com/llvm/llvm-project/commit/6b11573b8c5e3d36beee099dbe7347c2a007bf53 [1]
> > Reviewed-by: Reinette Chatre <reinette.chatre@...el.com>
> > Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> > ---
> 
> If there is a re-spin I think appropriate Fixes tags can be added:
> Fixes: 05b93417ce5b ("x86/intel_rdt/mba: Add primary support for Memory Bandwidth Allocation (MBA)")
> Fixes: 4d05bf71f157 ("x86/resctrl: Introduce AMD QOS feature") 
> 
> I am not familiar with stable rules related to compiler impact but
> this may fall into the "it bothers people" category of fixes so
> a Cc: stable@...r.kernel.org sounds appropriate also.

Yes, I think it would be reasonable to have Fixes and a Cc: stable since
this can turn fatal with CONFIG_SECTION_MISMATCH_WARN_ONLY=n (even if
there should be no real issue at run time because these functions are
only called from __init code).

I'll send a v4 upon request from whoever will apply this. Otherwise,
here is a copy and pasteable block:

Cc: stable@...r.kernel.org
Fixes: 05b93417ce5b ("x86/intel_rdt/mba: Add primary support for Memory Bandwidth Allocation (MBA)")
Fixes: 4d05bf71f157 ("x86/resctrl: Introduce AMD QOS feature")

Cheers,
Nathan