linux-kernel - Re: [PATCH] kthread: Use TASK_IDLE state for newly created kernel threads

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Message-ID: <20200521055639.GA2337399@kroah.com>
Date:   Thu, 21 May 2020 07:56:39 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Pavan Kondeti <pkondeti@...eaurora.org>
Cc:     linux-kernel@...r.kernel.org,
        Vinayak Menon <vinmenon@...eaurora.org>,
        Ben Dooks <ben.dooks@...ethink.co.uk>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Liang Chen <cl@...k-chips.com>
Subject: Re: [PATCH] kthread: Use TASK_IDLE state for newly created kernel
 threads

On Thu, May 21, 2020 at 07:05:44AM +0530, Pavan Kondeti wrote:
> On Wed, May 20, 2020 at 08:18:58PM +0200, Greg Kroah-Hartman wrote:
> > On Wed, May 20, 2020 at 05:25:09PM +0530, Pavankumar Kondeti wrote:
> > > When kernel threads are created for later use, they will be in
> > > TASK_UNINTERRUPTIBLE state until they are woken up. This results
> > > in increased loadavg and false hung task reports. To fix this,
> > > use TASK_IDLE state instead of TASK_UNINTERRUPTIBLE when
> > > a kernel thread schedules out for the first time.
> > > 
> > > Signed-off-by: Pavankumar Kondeti <pkondeti@...eaurora.org>
> > > ---
> > >  kernel/kthread.c | 6 +++---
> > >  1 file changed, 3 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/kernel/kthread.c b/kernel/kthread.c
> > > index bfbfa48..b74ed8e 100644
> > > --- a/kernel/kthread.c
> > > +++ b/kernel/kthread.c
> > > @@ -250,7 +250,7 @@ static int kthread(void *_create)
> > >  	current->vfork_done = &self->exited;
> > >  
> > >  	/* OK, tell user we're spawned, wait for stop or wakeup */
> > > -	__set_current_state(TASK_UNINTERRUPTIBLE);
> > > +	__set_current_state(TASK_IDLE);
> > >  	create->result = current;
> > >  	/*
> > >  	 * Thread is going to call schedule(), do not preempt it,
> > > @@ -428,7 +428,7 @@ static void __kthread_bind(struct task_struct *p, unsigned int cpu, long state)
> > >  
> > >  void kthread_bind_mask(struct task_struct *p, const struct cpumask *mask)
> > >  {
> > > -	__kthread_bind_mask(p, mask, TASK_UNINTERRUPTIBLE);
> > > +	__kthread_bind_mask(p, mask, TASK_IDLE);
> > >  }
> > >  
> > >  /**
> > > @@ -442,7 +442,7 @@ void kthread_bind_mask(struct task_struct *p, const struct cpumask *mask)
> > >   */
> > >  void kthread_bind(struct task_struct *p, unsigned int cpu)
> > >  {
> > > -	__kthread_bind(p, cpu, TASK_UNINTERRUPTIBLE);
> > > +	__kthread_bind(p, cpu, TASK_IDLE);
> > >  }
> > >  EXPORT_SYMBOL(kthread_bind);
> > 
> > It's as if people never read mailing lists:
> > 	https://lore.kernel.org/r/DM6PR11MB3531D3B164357B2DC476102DDFC90@DM6PR11MB3531.namprd11.prod.outlook.com
> > 
> > Given that this is an identical resend of the previous patch, why are
> > you doing so, and what has changed since that original rejection?
> > 
> I did not know that it is attempted before. Thanks for pointing to the
> previous discussion. 
> 
> We have seen hung task reports from customers and it is due to a downstream
> change which create bunch of kernel threads for later use.

Do you have a pointer to that specific change?

> From Peter's reply, I understood that one must wake up the kthread
> after creation and put it in INTERRUPTIBLE sleep. I will pass on the
> message.

Just go fix that code, it sounds like it's in your tree already :)

thanks,

greg k-h