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

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Message-ID: <57DF56D4.50304@hpe.com>
Date:   Sun, 18 Sep 2016 23:09:08 -0400
From:   Waiman Long <waiman.long@....com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
CC:     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>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH] random: Fix kernel panic due to system_wq use before
 init

On 09/14/2016 03:19 PM, Linus Torvalds wrote:
> On Wed, Sep 14, 2016 at 12:14 PM, Waiman Long<waiman.long@....com>  wrote:
>> In the stack backtrace above, the kernel hadn't even reached SMP boot after
>> about 50s. That was extremely slow. I tried the 4.7.3 kernel and it booted
>> up fine. So I suspect that there may be too many interrupts going on and it
>> consumes most of the CPU cycles. The prime suspect is the random driver, I
>> think.
> Any chance of bisecting it at least partially? The random driver
> doesn't do interrupts itself, it just gets called by other drivers
> doing intterrupts. So if there are too many of them, that would be
> something else..
>
>                 Linus

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.

I have attached several slightly different panic messages that had 
happened in my testing. I know little about the EFI code and so I am not 
sure if it is a kernel problem, firmware problem or a combination of 
both. Hopefully someone with knowledge on this code will shed light on 
this problem.

Cheers,
Longman

View attachment "panic.log" of type "text/plain" (25816 bytes)