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

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Date:   Wed, 3 Mar 2021 17:25:37 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ben Skeggs <bskeggs@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, 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 2020-11-21 11:55:48 [+0100], Thomas Gleixner wrote:
> 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.

Just a friendly ping that this is still in my queue…

Ben could please reply here stating your view of the situation?

> Thanks,
> 
>         tglx

Sebastian