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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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