linux-kernel - Re: [PATCH] x86/PAT: priority the PAT warn to error to highlight the developer

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Message-ID: <20190930120211.GE29694@zn.tnic>
Date:   Mon, 30 Sep 2019 14:02:43 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     jun.zhang@...el.com
Cc:     dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org,
        tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        bo.he@...el.com, x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/PAT: priority the PAT warn to error to highlight the
 developer

On Sun, Sep 29, 2019 at 03:20:31PM +0800, jun.zhang@...el.com wrote:
> From: zhang jun <jun.zhang@...el.com>
> 
> Documentation/x86/pat.txt says:
> set_memory_uc() or set_memory_wc() must use together with set_memory_wb()

I had to open that file to see what it actually says - btw, the filename
is pat.rst now - and you're very heavily paraphrasing what is there. So
try again explaining what the requirement is.

> if break the PAT attribute, there are tons of warning like:
> [   45.846872] x86/PAT: NDK MediaCodec_:3753 map pfn RAM range req

That's some android NDK thing, it seems: "The Android NDK is a toolset
that lets you implement parts of your app in native code,... " lemme
guess, they have a kernel module?

> write-combining for [mem 0x1e7a80000-0x1e7a87fff], got write-back
> and in the extremely case, we see kernel panic unexpected like:
> list_del corruption. prev->next should be ffff88806dbe69c0,
> but was ffff888036f048c0

This is not really helpful. You need to explain what exactly you're
doing - not shortening the error messages.

> so it's better to priority the warn to error to highlight to
> remind the developer.

Whut?

>From reading what is trying hard to be a sentence, I can only guess what
you're trying to say here. And it doesn't make it clear why is pr_warn()
not enough and it has to be pr_err().

> Signed-off-by: zhang jun <jun.zhang@...el.com>
> Signed-off-by: he, bo <bo.he@...el.com>

And this SOB chain is wrong.

> ---
>  arch/x86/mm/pat.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
> index d9fbd4f69920..43a4dfdcedc8 100644
> --- a/arch/x86/mm/pat.c
> +++ b/arch/x86/mm/pat.c
> @@ -897,7 +897,7 @@ static int reserve_pfn_range(u64 paddr, unsigned long size, pgprot_t *vma_prot,
>  
>  		pcm = lookup_memtype(paddr);
>  		if (want_pcm != pcm) {
> -			pr_warn("x86/PAT: %s:%d map pfn RAM range req %s for [mem %#010Lx-%#010Lx], got %s\n",
> +			pr_err("x86/PAT: %s:%d map pfn RAM range req %s for [mem %#010Lx-%#010Lx], got %s!!!\n",

Three "!!!" would make this more urgent, huh?

How about you make the error message more informative and user-friendly,
instead?

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette