cpuset: fix the problem that cpuset_mem_spread_node() returns an offline node

cpuset_mem_spread_node() returns an offline node, and causes an oops.

This patch fixes it by initializing task->mems_allowed to
node_states[N_HIGH_MEMORY], and updating task->mems_allowed when doing
memory hotplug.

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Acked-by: David Rientjes <rientjes@google.com>
Reported-by: Nick Piggin <npiggin@suse.de>
Tested-by: Nick Piggin <npiggin@suse.de>
Cc: Paul Menage <menage@google.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 13 insertions, 9 deletions

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index ba401fab459f..5d38bd74483c 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -920,9 +920,6 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
  *    call to guarantee_online_mems(), as we know no one is changing
  *    our task's cpuset.
  *
- *    Hold callback_mutex around the two modifications of our tasks
- *    mems_allowed to synchronize with cpuset_mems_allowed().
- *
  *    While the mm_struct we are migrating is typically from some
  *    other task, the task_struct mems_allowed that we are hacking
  *    is for our current task, which must allocate new pages for that
@@ -1391,11 +1388,10 @@ static void cpuset_attach(struct cgroup_subsys *ss, struct cgroup *cont,
 
         if (cs == &top_cpuset) {
                 cpumask_copy(cpus_attach, cpu_possible_mask);
-                to = node_possible_map;
         } else {
                 guarantee_online_cpus(cs, cpus_attach);
-                guarantee_online_mems(cs, &to);
         }
+        guarantee_online_mems(cs, &to);
 
         /* do per-task migration stuff possibly for each in the threadgroup */
         cpuset_attach_task(tsk, &to, cs);
@@ -2090,15 +2086,23 @@ static int cpuset_track_online_cpus(struct notifier_block *unused_nb,
 static int cpuset_track_online_nodes(struct notifier_block *self,
                                 unsigned long action, void *arg)
 {
+        nodemask_t oldmems;
+
         cgroup_lock();
         switch (action) {
         case MEM_ONLINE:
-        case MEM_OFFLINE:
+                oldmems = top_cpuset.mems_allowed;
                 mutex_lock(&callback_mutex);
                 top_cpuset.mems_allowed = node_states[N_HIGH_MEMORY];
                 mutex_unlock(&callback_mutex);
-                if (action == MEM_OFFLINE)
-                        scan_for_empty_cpusets(&top_cpuset);
+                update_tasks_nodemask(&top_cpuset, &oldmems, NULL);
+                break;
+        case MEM_OFFLINE:
+                /*
+                 * needn't update top_cpuset.mems_allowed explicitly because
+                 * scan_for_empty_cpusets() will update it.
+                 */
+                scan_for_empty_cpusets(&top_cpuset);
                 break;
         default:
                 break;
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 82ed0ea15194..83911c780175 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -219,7 +219,7 @@ int kthreadd(void *unused)
         set_task_comm(tsk, "kthreadd");
         ignore_signals(tsk);
         set_cpus_allowed_ptr(tsk, cpu_all_mask);
-        set_mems_allowed(node_possible_map);
+        set_mems_allowed(node_states[N_HIGH_MEMORY]);
 
         current->flags |= PF_NOFREEZE | PF_FREEZER_NOSIG;