linux-kernel - Re: [crash] PANIC: double fault, error

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Message-ID: <20171125093243.4gmkelmyb4mnhvos@gmail.com>
Date:   Sat, 25 Nov 2017 10:32:43 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Andy Lutomirski <luto@...capital.net>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [crash] PANIC: double fault, error_code: 0x0


* Ingo Molnar <mingo@...nel.org> wrote:

> > (Also note that in my config NR_CPUS is at 128 - defconfigs are 64.)
> 
> The simplest padding I found is the one below - this indicates some sort of 
> section sizing or page table setup bug (or page alignment bug) and makes races and 
> other bugs less likely.
> 
> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> index 4ac952080869..ea992ca4e74f 100644
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -547,6 +547,8 @@ END(irq_entries_start)
>  	ud2
>  .Lokay_\@:
>  	addq $8, %rsp
> +#else
> +	.rep 64; nop; .endr

Also note that turning off CONFIG_UNWINDER_ORC also solves the crash. I did that 
in an attempt to get a different backtrace.

So it's either unwinder related, or seemingly minor changes to code 
alignment/placement will make the bug go away.

Thanks,

	Ingo