linux-kernel - Re: [patch 17/18] sched: Enable might

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Message-ID: <20170516091412.77987500@gandalf.local.home>
Date:   Tue, 16 May 2017 09:14:12 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [patch 17/18] sched: Enable might_sleep() checks early

On Tue, 16 May 2017 09:33:52 +0200 (CEST)
Thomas Gleixner <tglx@...utronix.de> wrote:


> Darn, forgot about PREEMPT_VOLUNTARY and that excellent changelog does not
> mention it either. 
> 
> > So if we schedule to the kernel_init() task before we set kthreadd_task
> > we'll try and spawn kthreads and OOPS.  
> 
> So back to Stevens question. No, we can't set the state earlier than right
> before schedule() simply because with PREEMPT preemption _is_ actually
> disabled and kernel_kthread() will trigger might_sleep() splats.

So a comment in the code mentioning PREEMPT_VOLUNTARY might be
advantageous.

> 
> What a mess.

Indeed.

-- Steve