linux-kernel - Re: [PATCH 1/2] kthread: Move prio/affinite change into the newly created thread

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Message-ID: <87a6vbnfm3.fsf@nanos.tec.linutronix.de>
Date:   Sat, 21 Nov 2020 11:55:48 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, Ben Skeggs <bskeggs@...hat.com>,
        Mike Galbraith <efault@....de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 1/2] kthread: Move prio/affinite change into the newly created thread

On Tue, Nov 17 2020 at 13:45, Peter Zijlstra wrote:
> On Tue, Nov 10, 2020 at 12:38:47PM +0100, Sebastian Andrzej Siewior wrote:
>
> Moo... yes this is certainly the easiest solution, because nouveau is a
> horrible rats nest. But when I spoke to Greg KH about this, he suggested
> nouveau ought to be fixed.
>
> Ben, I got terminally lost when trying to untangle nouvea init, is there
> any chance this can be fixed to not hold that nvkm_device::mutex thing
> while doing request_irq() ?

OTOH, creating a dependency chain vs. cpuset_rwsem and whatever lock is
held by the caller via request_irq() or kthread_create() is not
necessarily restricted to the nivea driver. struct device::mutex (not
the nkvm_device::mutex) is always held when a driver is probed.

The cpuset_rwsem -> mmap_lock dependency is a given, so we're one step
away from a circular dependency vs. mmap_lock.

That was my reasoning to move the stuff out into the thread context.

Thanks,

        tglx