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

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Date:   Fri, 22 Sep 2017 11:35:33 +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 16:41 +0200, Markus Trippelsdorf wrote:
> 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.

So perhaps something like this:

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 525157ca25cb..741687be3b0d 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -142,6 +142,9 @@ static inline const char *get_task_state(struct task_struct *tsk)
 
 	BUILD_BUG_ON(1 + ilog2(TASK_REPORT) != ARRAY_SIZE(task_state_array)-1);
 
+	if (tsk->state == TASK_IDLE)
+		return "I (idle)";
+
 	return task_state_array[fls(state)];
 }
 
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 18a6966567da..83681990d3f9 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5188,7 +5188,8 @@ void show_state_filter(unsigned long state_filter)
 		 */
 		touch_nmi_watchdog();
 		touch_all_softlockup_watchdogs();
-		if (!state_filter || (p->state & state_filter))
+		if (!state_filter ||
+		    (!(p->state == TASK_IDLE) && p->state & state_filter))
 			sched_show_task(p);
 	}
 
-- 
Markus