linux-kernel - Re: [RFC PATCH v1 19/57] crash: Remove PAGE

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Message-ID: <Zw3luHGG3LqHge2m@MiWiFi-R3L-srv>
Date: Tue, 15 Oct 2024 11:47:04 +0800
From: Baoquan He <bhe@...hat.com>
To: Ryan Roberts <ryan.roberts@....com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Anshuman Khandual <anshuman.khandual@....com>,
	Ard Biesheuvel <ardb@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	David Hildenbrand <david@...hat.com>,
	Greg Marsden <greg.marsden@...cle.com>,
	Ivan Ivanov <ivan.ivanov@...e.com>,
	Kalesh Singh <kaleshsingh@...gle.com>,
	Marc Zyngier <maz@...nel.org>, Mark Rutland <mark.rutland@....com>,
	Matthias Brugger <mbrugger@...e.com>,
	Miroslav Benes <mbenes@...e.cz>, Will Deacon <will@...nel.org>,
	kexec@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC PATCH v1 19/57] crash: Remove PAGE_SIZE compile-time
 constant assumption

On 10/14/24 at 11:58am, Ryan Roberts wrote:
> To prepare for supporting boot-time page size selection, refactor code
> to remove assumptions about PAGE_SIZE being compile-time constant. Code
> intended to be equivalent when compile-time page size is active.
> 
> Updated BUILD_BUG_ON() to test against limit.
> 
> Signed-off-by: Ryan Roberts <ryan.roberts@....com>
> ---
> 
> ***NOTE***
> Any confused maintainers may want to read the cover note here for context:
> https://lore.kernel.org/all/20241014105514.3206191-1-ryan.roberts@arm.com/
> 
>  kernel/crash_core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> index 63cf89393c6eb..978c600a47ac8 100644
> --- a/kernel/crash_core.c
> +++ b/kernel/crash_core.c
> @@ -465,7 +465,7 @@ static int __init crash_notes_memory_init(void)
>  	 * Break compile if size is bigger than PAGE_SIZE since crash_notes
>  	 * definitely will be in 2 pages with that.
>  	 */
> -	BUILD_BUG_ON(size > PAGE_SIZE);
> +	BUILD_BUG_ON(size > PAGE_SIZE_MIN);

This should be OK. While one thing which could happen is if selected size
is 64K, PAGE_SIZE_MIN is 4K, it will issue a false-positive warning when
compiling while actual it's not a problem during running. Not sure if
that could happen on arm64. Anyway, we can check the crash_notes to get
why it's so big when it really happens. So,

Acked-by: Baoquan He <bhe@...hat.com>

>  
>  	crash_notes = __alloc_percpu(size, align);
>  	if (!crash_notes) {
> -- 
> 2.43.0
> 
>