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> Tested-by: Marcin Ślusarz <marcin.slusarz@gmail.com>
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@ -1679,12 +1679,10 @@ static int rcu_oom_notify(struct notifier_block *self,
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*/
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*/
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atomic_set(&oom_callback_count, 1);
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atomic_set(&oom_callback_count, 1);
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get_online_cpus();
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for_each_online_cpu(cpu) {
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for_each_online_cpu(cpu) {
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smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
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smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
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cond_resched_rcu_qs();
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cond_resched_rcu_qs();
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}
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}
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put_online_cpus();
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/* Unconditionally decrement: no need to wake ourselves up. */
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/* Unconditionally decrement: no need to wake ourselves up. */
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atomic_dec(&oom_callback_count);
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atomic_dec(&oom_callback_count);
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