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

Joel Fernandes
2019-06-27T17:46:45Z

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: