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

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Message-ID: <57D9A633.2030904@hpe.com>
Date:   Wed, 14 Sep 2016 15:34:11 -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>
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 can try, but the 16-socket system that I have at the moment takes a 
long time (more than an hour) for one shutdown-reboot cycle. It may not 
be really more interrupts in 4.8, it may be that the random driver just 
somehow run very slow on my test machine as it seems to have a major 
rewrite in the 4.8 cycle. So I would like to solicit what sort of test 
that I can run to pinpoint where the problem is. I currently has the 
machine till the end of the week.

Cheers,
Longman