linux-kernel - Re: There is a Tasks RCU stall warning

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Message-Id: <20170411213208.GG1600@linux.vnet.ibm.com>
Date:   Tue, 11 Apr 2017 14:32:08 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: There is a Tasks RCU stall warning

On Tue, Apr 11, 2017 at 05:21:07PM -0400, Steven Rostedt wrote:
> On Tue, 11 Apr 2017 14:18:02 -0700
> "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:
> 
> > Hello, Steve,
> > 
> > Network connectivity issues...  :-/
> 
> ug
> 
> > There is already a Tasks RCU stall warning, but it waits for
> > ten -minutes- before complaining.  You can change this with the
> > rcupdate.rcu_task_stall_timeout kernel boot parameter, if you wish.
> > 
> > Or did you wait longer than ten minutes?
> 
> Hmm, I may have waited longer. But I can try again and shorten the
> timeout.

Failing that, you might try carefully placed printk() calls in
rcu_tasks_kthread().  The loop spinning on non-empty rcu_tasks_holdouts()
should loop at most once per second, so you can get away with quite a
bit of instrumentation.  Unlike much of the rest of RCU.  ;-)

							Thanx, Paul