cpuset: fix possible races in cpu/memory hotplug

Change to cpuset->cpus_allowed and cpuset->mems_allowed should be protected
by callback_mutex, otherwise the reader may read wrong cpus/mems. This is
cpuset's lock rule.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 3 deletions

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index ee5ec386aa8b..31737957cb62 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -2070,7 +2070,9 @@ static int cpuset_track_online_cpus(struct notifier_block *unused_nb,
         }
 
         cgroup_lock();
+        mutex_lock(&callback_mutex);
         cpumask_copy(top_cpuset.cpus_allowed, cpu_online_mask);
+        mutex_unlock(&callback_mutex);
         scan_for_empty_cpusets(&top_cpuset);
         ndoms = generate_sched_domains(&doms, &attr);
         cgroup_unlock();
@@ -2093,11 +2095,12 @@ static int cpuset_track_online_nodes(struct notifier_block *self,
         cgroup_lock();
         switch (action) {
         case MEM_ONLINE:
-                top_cpuset.mems_allowed = node_states[N_HIGH_MEMORY];
-                break;
         case MEM_OFFLINE:
+                mutex_lock(&callback_mutex);
                 top_cpuset.mems_allowed = node_states[N_HIGH_MEMORY];
-                scan_for_empty_cpusets(&top_cpuset);
+                mutex_unlock(&callback_mutex);
+                if (action == MEM_OFFLINE)
+                        scan_for_empty_cpusets(&top_cpuset);
                 break;
         default:
                 break;