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From:   Joel Fernandes <joel@joelfernandes.org>
Date:   Thu, 27 Jun 2019 13:46:27 -0400
Message-ID: <CAEXW_YTmx3wFKuiLyrQO6uSPYAL179EPa6N3WO7qZahccCs-pg@mail.gmail.com>
Subject: Re: [RFC] Deadlock via recursive wakeup via RCU with threadirqs
To:     Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc:     Steven Rostedt <rostedt@goodmis.org>,
        "Paul E. McKenney" <paulmck@linux.ibm.com>,
        rcu <rcu@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Josh Triplett <josh@joshtriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Lai Jiangshan <jiangshanlai@gmail.com>
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On Thu, Jun 27, 2019 at 1:43 PM Joel Fernandes <joel@joelfernandes.org> wrote:
>
> On Thu, Jun 27, 2019 at 11:40 AM Sebastian Andrzej Siewior
> <bigeasy@linutronix.de> wrote:
> >
> > 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?
>
> I could reproduce this as well just booting Linus tree with threadirqs
> command line and running rcutorture. In 15 seconds or so it locks
> up... gdb backtrace shows the recursive lock:

Sorry that got badly wrapped, so I pasted it here:
https://hastebin.com/ajivofomik.shell