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SubjectRe: cpu_hotplug vs oom_notify_list: possible circular locking dependency detected
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>
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