From 9a54f98e341d09793247a6e598012edefb5ae7cb Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 14 Jul 2015 16:24:14 -0700 Subject: [PATCH] rcu: Don't disable CPU hotplug during OOM notifiers MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Reported-by: David Rientjes Signed-off-by: Paul E. McKenney Acked-by: David Rientjes Tested-by: Marcin Ślusarz --- 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); -- GitLab