linux-kernel - Re: [PATCH] random: Fix kernel panic due to system

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Date:   Mon, 19 Sep 2016 10:25:31 +0100
From:   Matt Fleming <matt@...eblueprint.co.uk>
To:     Waiman Long <waiman.long@....com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Theodore Ts'o <tytso@....edu>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Scott J Norton <scott.norton@....com>,
        Douglas Hatch <doug.hatch@....com>,
        Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH] random: Fix kernel panic due to system_wq use before init

On Sun, 18 Sep, at 11:09:08PM, Waiman Long wrote:
> 
> I have finally finished bisecting the problem. I was wrong in saying that
> the 4.7.3 kernel had no problem. It did have. There were some slight
> differences between the 4.8 and 4.7 kernel config files that I used. After
> some further testing, it was found that the bootup problem only happened
> when the following kernel config option was defined:
> 
> CONFIG_EFI_MIXED=y
> 
> Bisecting reviewed that the following 4.6 patch was the first patch that had
> this problem:
> 
> c9f2a9a65e4855b74d92cdad688f6ee4a1a323ff
> [PATCH] x86/efi: Hoist page table switching code into efi_call_virt()
> 
> I did testing on my test system with three different partition sizes:
> 1) 16-socket Broadwell-EX with 12TB memory
> 2) 8-socket Broadwell-EX with 6TB memory
> 3) 4-socket Broadwell-EX with 3TB memory
> 
> Only the 16-socket and 8-socket configurations had this problem. I am not
> sure if over 4TB of main memory is a factor or not.

Yes, I think it's a safe bet that the amount of main memory is a major
factor here. Thanks for the report.

The only real difference when CONFIG_EFI_MIXED is enabled for 64-bit
kernel and 64-bit firmware is that main memory will be mapped into the
EFI page tables at its physical addresses.

I'll go stare at the code and get back to you.