linux-kernel - Re: Worker threads in D state since c5a94a618e7ac86 (workqueue: Use TASK

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Message-ID: <20170921144127.GA236@x4>
Date:   Thu, 21 Sep 2017 16:41:27 +0200
From:   Markus Trippelsdorf <markus@...ppelsdorf.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: Worker threads in D state since c5a94a618e7ac86 (workqueue: Use
 TASK_IDLE)

On 2017.09.21 at 14:30 +0200, Peter Zijlstra wrote:
> On Thu, Sep 21, 2017 at 01:08:42PM +0200, Markus Trippelsdorf wrote:
> > On 2017.09.11 at 16:21 +0200, Markus Trippelsdorf wrote:
> > > On 2017.09.11 at 06:11 -0700, Tejun Heo wrote:
> > > > Hello,
> > > >
> > > > On Sun, Sep 10, 2017 at 09:36:53AM +0200, Markus Trippelsdorf wrote:
> > > > > Since:
> > > > >
> > > > >  commit c5a94a618e7ac86b20f53d947f68d7cee6a4c6bc
> > > > >  Author: Peter Zijlstra <peterz@...radead.org>
> > > > >  Date:   Wed Aug 23 13:58:44 2017 +0200
> > > > >
> > > > >      workqueue: Use TASK_IDLE
> > > > >
> > > > >
> > > > > all worker threads are in D state. They all show up when using "magic
> > > > > SysRq w". In htop they all have big fat red 'D' in the state column.
> > > > > Is this really desirable?
> > > > >
> > > > > I have attached the output of "ps aux" after boot and the SysRq-w
> > > > > output.
> > > >
> > > > Hmm.... looks like we better revert until we figure out how this
> > > > should get presented in debugging facilities / to userspace.  Peter?
> > > 
> > > BTW rcu recently introduced the same issue:
> > > 
> > >  commit d5374226c3e444239e063f005dfb59cae4390db4
> > >  Author: Luis R. Rodriguez <mcgrof@...nel.org>
> > >  Date:   Tue Jun 20 14:45:47 2017 -0700
> > > 
> > >      rcu: Use idle versions of swait to make idle-hack clear
> > 
> > Ping? 
> > You may call it a cosmetic issue, but still it makes debugging much
> > harder. Finding "real" blocked tasks is now like finding a needle in a
> > haystack.
> 
> Sorry, was out traveling. We can easily fix sysrq-w, not sure we can do
> much about htop (I've never seen it).
> 
> I suppose we can try and make the state character not be D, is that
> really worth the trouble, or would it simply break htop if we were to
> return a new character?

It seems to work. Simply returning "I (idle)" from get_task_state() in
fs/proc/array.c when the state is TASK_IDLE does the trick.
I've tested top, htop and ps.

-- 
Markus