linux-kernel - Re: [PATCH v2 1/2] x86/ioremap: introduce helper to implement xxx_is_setup

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Message-ID: <b49096ad-fbfd-393f-9f35-944eeecd91db@amd.com>
Date: Wed, 20 Nov 2024 08:14:39 -0600
From: Tom Lendacky <thomas.lendacky@....com>
To: Ingo Molnar <mingo@...nel.org>
Cc: Baoquan He <bhe@...hat.com>, linux-kernel@...r.kernel.org, bp@...en8.de,
 x86@...nel.org
Subject: Re: [PATCH v2 1/2] x86/ioremap: introduce helper to implement
 xxx_is_setup_data()

On 11/20/24 02:25, Ingo Molnar wrote:
> 
> * Tom Lendacky <thomas.lendacky@....com> wrote:
> 
>>>  /*
>>>   * Examine the physical address to determine if it is boot data by checking
>>>   * it against the boot params setup_data chain.
>>>   */
>>> -static bool memremap_is_setup_data(resource_size_t phys_addr,
>>> -				   unsigned long size)
>>> +static bool __ref __memremap_is_setup_data(resource_size_t phys_addr,
>>
>> Oh, I see why the __ref is needed now, because this calls an __init
>> function based on the early bool.
>>
>> While this nicely consolidates the checking, I'll let the x86
>> maintainers decide whether they like that an __init function is calling
>> a non __init function.
> 
> So why would it be a problem? Only non-__init calling __init is a bug, 
> because __init functions cease to exist after early bootup. Also, 
> calling certain kernel subsystems too early, before they are 
> initialized, is a bug as well.

I brought it up because that is what could happen if the wrong boolean
value is supplied to the helper function. The helper function is marked
non-__init but calls a __init function if the boolean value is true, hence
the need for the __ref tagging.

But, I don't anticipate that this helper will be called by anything else
than what is currently calling it and the proper boolean values are set on
those calls.

I just wanted to raise awareness. I'm ok with using __ref, just wanted to
make sure everyone else is, too.

Thanks,
Tom

> 
> But calling non-__init functions that have initialized already is like 
> totally normal: printk() for example, but also all locking facilities, 
> etc.
> 
> Am I missing anything here?
> 
> Thanks,
> 
> 	Ingo