linux-kernel - Re: [RFC] Deadlock via recursive wakeup via RCU with threadirqs

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Date:   Thu, 27 Jun 2019 17:40:11 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Joel Fernandes <joel@...lfernandes.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        "Paul E. McKenney" <paulmck@...ux.ibm.com>,
        rcu <rcu@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Triplett <josh@...htriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>
Subject: Re: [RFC] Deadlock via recursive wakeup via RCU with threadirqs

On 2019-06-27 11:37:10 [-0400], Joel Fernandes wrote:
> Sebastian it would be nice if possible to trace where the
> t->rcu_read_unlock_special is set for this scenario of calling
> rcu_read_unlock_special, to give a clear idea about whether it was
> really because of an IPI. I guess we could also add additional RCU
> debug fields to task_struct (just for debugging) to see where there
> unlock_special is set.
> 
> Is there a test to reproduce this, or do I just boot an intel x86_64
> machine with "threadirqs" and run into it?

Do you want to send me a patch or should I send you my kvm image which
triggers the bug on boot?

Sebastian