Re: [RESEND][PATCH 1/2] cpuset: fix the problem that cpuset_mem_spread_node() returns an offline node (v2)

[Nick Piggin <npiggin@suse.de>]

This one fixed the oops for me, thanks for working on it.

Reported-and-tested-by: Nick Piggin <npiggin@suse.de>

It could be a stable@ candidate because it trivially oopses
when the cpuset_mem_spread_node option is used.

On Tue, Mar 16, 2010 at 08:10:43PM +0800, Miao Xie wrote:
> 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>
> ---
>  init/main.c      |    2 +-
>  kernel/cpuset.c  |   20 ++++++++++++--------
>  kernel/kthread.c |    2 +-
>  3 files changed, 14 insertions(+), 10 deletions(-)
> 
> diff --git a/init/main.c b/init/main.c
> index a1ab78c..cbead27 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -858,7 +858,7 @@ 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..5d38bd7 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 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
>