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Date: Thu, 23 May 2024 16:49:16 -0700
From: Kees Cook <keescook@chromium.org>
To: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Cc: mattst88@gmail.com, linux-alpha@vger.kernel.org,
	linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: Regression bisected to f2f84b05e02b (bug: consolidate
 warn_slowpath_fmt() usage)
Message-ID: <202405231647.69CAA404D8@keescook>
References: <20200602024804.GA3776630@p50-ethernet.mattst88.com>
 <20240521184652.1875074-1-glaubitz@physik.fu-berlin.de>
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In-Reply-To: <20240521184652.1875074-1-glaubitz@physik.fu-berlin.de>

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