linux-kernel - Re: cpu stopper threads and load balancing leads to deadlock

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Message-ID: <20180503145221.GE12217@hirez.programming.kicks-ass.net>
Date:   Thu, 3 May 2018 16:52:21 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     Mike Galbraith <efault@....de>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        Michal Hocko <mhocko@...e.com>
Subject: Re: cpu stopper threads and load balancing leads to deadlock

On Thu, May 03, 2018 at 07:39:41AM -0700, Paul E. McKenney wrote:
> Huh.
> 
> No, RCU_NONIDLE() only works for idle, not for offline.

Oh bummer..

> Maybe...  Let me take a look.  There must be some way to mark a
> specific lock acquisition and release as being lockdep-invisible...

But I suspect it flags a real issue. Shutting it up isn't the issue as
such. There could be a concurrent sched domain rebuild while we do this
setup, and if we free that domain while we're looking at it, bad things
happen.

... I wonder what brought this failure to pass now. This code has been
like this a for a long time.