From: "Paul E. McKenney" <[email protected]> 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 <[email protected]> Reported-by: David Rientjes <[email protected]> Signed-off-by: Paul E. McKenney <[email protected]> Acked-by: David Rientjes <[email protected]> --- kernel/rcu/tree_plugin.h | 2 -- 1 file changed, 2 deletions(-) diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 9e922f111d63..80a7c17907fe 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -1679,12 +1679,10 @@ static int rcu_oom_notify(struct notifier_block *self, */ atomic_set(&oom_callback_count, 1); - get_online_cpus(); for_each_online_cpu(cpu) { smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1); cond_resched_rcu_qs(); } - put_online_cpus(); /* Unconditionally decrement: no need to wake ourselves up. */ atomic_dec(&oom_callback_count); -- 1.8.1.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
