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

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Date:   Wed, 14 Sep 2016 15:55:51 -0400
From:   Tejun Heo <tj@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Waiman Long <Waiman.Long@....com>, 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

Hello, Linus.

On Wed, Sep 14, 2016 at 12:14:30PM -0700, Linus Torvalds wrote:
> I'm wondering if we couldn't just initialize "system_wq" earlier.
> Right now init_workqueues() is an "early_initcall()", so it's at the
> same priority as a number of other random early initcalls. My gut
> feeling is that it should be initialized even earlier, with the
> scheduler.
> 
> Because dammit, we use "schedule_work()" as if it was a pretty core
> scheduler thing, and having to have some odd knowledge of system_wq
> initialization details in the rest of the kernel sounds really really
> wrong.
> 
> I don't think the random code is at all special in maybe wanting to
> schedule some work despite being an "early" initcall.
> 
> Adding Tejun to the cc, and quoting the whole email.
> 
> Tejun, comments?

We've used keventd_up() for this purpose and it hasn't been big enough
an issue as workqueue usages during earlyboot are very rare (only five
users right now).  But, yeah, it's getting used a more and more and
there's no harm in moving it to earlier.  I'll see how early I can
push it.

Thanks.

-- 
tejun