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Subject[PATCH 1/4] cpuset: fix the problem that cpuset_mem_spread_node() returns an offline node(was: Re: [regression] cpuset,mm: update tasks' mems_allowed in time (58568d2))
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>
---
init/main.c | 2 +-
kernel/cpuset.c | 30 ++++++++++++++++++++++--------
kernel/kthread.c | 2 +-
3 files changed, 24 insertions(+), 10 deletions(-)
diff --git a/init/main.c b/init/main.c
index c75dcd6..acb4edf 100644
--- a/init/main.c
+++ b/init/main.c
@@ -848,7 +848,7 @@ static int __init kernel_init(void * unused)
/*
* init can allocate pages on any node
*/
- set_mems_allowed(node_possible_map);
+ set_mems_allowed(node_states[N_HIGH_MEMORY]);
/*
* init can run on any cpu.
*/
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index ba401fa..f732ff7 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
@@ -936,9 +933,23 @@ static void cpuset_migrate_mm(struct mm_struct *mm, const nodemask_t *from,

tsk->mems_allowed = *to;

+ /*
+ * After current->mems_allowed is set to a new value, current will
+ * allocate new pages for the migrating memory region. So we must
+ * ensure that update of current->mems_allowed have been completed
+ * by this moment.
+ */
+ smp_wmb();
do_migrate_pages(mm, from, to, MPOL_MF_MOVE_ALL);

guarantee_online_mems(task_cs(tsk),&tsk->mems_allowed);
+
+ /*
+ * After doing migrate pages, current will allocate new pages for
+ * itself not the other tasks. So we must ensure that update of
+ * current->mems_allowed have been completed by this moment.
+ */
+ smp_wmb();
}

/*
@@ -1391,11 +1402,10 @@ 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 +2100,19 @@ 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:
+ scan_for_empty_cpusets(&top_cpuset);
break;
default:
break;
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 82ed0ea..83911c7 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;

--
1.6.5.2



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