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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2015-07-14 16:24:14 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2015-07-22 15:27:43 -0700
commit9a54f98e341d09793247a6e598012edefb5ae7cb (patch)
tree4a30b36698274e22b17651a0cad70500af2cef21
parent3ad81779ad35cd2e2ab34ba3f47f6f485696a105 (diff)
downloadlinux-sh-9a54f98e341d09793247a6e598012edefb5ae7cb.tar.gz
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>
-rw-r--r--kernel/rcu/tree_plugin.h2
1 files changed, 0 insertions, 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);