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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>
steinar/wifi_calib_4_9_kernel
Paul E. McKenney 2015-07-14 16:24:14 -07:00
parent 3ad81779ad
commit 9a54f98e34
1 changed files with 0 additions and 2 deletions
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2
kernel/rcu/tree_plugin.h
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@ -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);