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SubjectRe: cpu_hotplug vs oom_notify_list: possible circular locking dependency detected
On Thu, Jul 16, 2015 at 02:01:56PM -0700, David Rientjes wrote:
> On Wed, 15 Jul 2015, Paul E. McKenney wrote:
>
> > On Tue, Jul 14, 2015 at 04:48:24PM -0700, David Rientjes wrote:
> > > On Tue, 14 Jul 2015, Paul E. McKenney wrote:
> > >
> > > > commit a1992f2f3b8e174d740a8f764d0d51344bed2eed
> > > > Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > > > Date: Tue Jul 14 16:24:14 2015 -0700
> > > >
> > > > rcu: Don't disable CPU hotplug during OOM notifiers
> > > >
> > > > RCU's rcu_oom_notify() disables CPU hotplug in order to stabilize the
> > > > list of online CPUs, which it traverses. However, this is completely
> > > > pointless because smp_call_function_single() will quietly fail if invoked
> > > > on an offline CPU. Because the count of requests is incremented in the
> > > > rcu_oom_notify_cpu() function that is remotely invoked, everything works
> > > > nicely even in the face of concurrent CPU-hotplug operations.
> > > >
> > > > Furthermore, in recent kernels, invoking get_online_cpus() from an OOM
> > > > notifier can result in deadlock. This commit therefore removes the
> > > > call to get_online_cpus() and put_online_cpus() from rcu_oom_notify().
> > > >
> > > > Reported-by: Marcin Ślusarz <marcin.slusarz@gmail.com>
> > > > Reported-by: David Rientjes <rientjes@google.com>
> > > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > >
> > > Acked-by: David Rientjes <rientjes@google.com>
> >
> > Thank you!
> >
> > Any news on whether or not it solves the problem?
> >
>
> Marcin, is your lockdep violation reproducible? If so, does this patch
> fix it?

I finally found enough time today to test it. I can reproduce it without
the above patch and can't with. So:
Tested-by: Marcin Ślusarz <marcin.slusarz@gmail.com>

Thanks,
Marcin


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