linux-kernel - Re: Regression bisected to f2f84b05e02b (bug: consolidate warn_slowpath

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Date: Thu, 23 May 2024 16:49:16 -0700
From: Kees Cook <keescook@...omium.org>
To: John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
Cc: mattst88@...il.com, linux-alpha@...r.kernel.org,
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Regression bisected to f2f84b05e02b (bug: consolidate
 warn_slowpath_fmt() usage)

On Tue, May 21, 2024 at 08:46:52PM +0200, John Paul Adrian Glaubitz wrote:
> Hi,
> 
> Replacing the calls to raw_smp_processor_id() in __warn() with just "0" fixes the problem for me:
> 
> diff --git a/kernel/panic.c b/kernel/panic.c
> index 8bff183d6180..12f6cea6b8b0 100644
> --- a/kernel/panic.c
> +++ b/kernel/panic.c
> @@ -671,11 +671,11 @@ void __warn(const char *file, int line, void *caller, unsigned taint,
>  
>         if (file)
>                 pr_warn("WARNING: CPU: %d PID: %d at %s:%d %pS\n",
> -                       raw_smp_processor_id(), current->pid, file, line,
> +                       0, current->pid, file, line,
>                         caller);
>         else
>                 pr_warn("WARNING: CPU: %d PID: %d at %pS\n",
> -                       raw_smp_processor_id(), current->pid, caller);
> +                       0, current->pid, caller);
>  
>  #pragma GCC diagnostic push
>  #ifndef __clang__
> 
> So, I assume the problem is that SMP support is not fully initialized at this
> point yet such that raw_smp_processor_id() causes the zero pointer dereference.

But how does the commit change that? It called __warn() before too.

Is this an inlining bug?

-- 
Kees Cook