Re: [PATCH -mmotm 3/4] memcg: avoid dead lock caused by racebetween oom and cpuset_attach

[Daisuke Nishimura]

On Mon, 8 Dec 2008 11:05:11 +0900, Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx> wrote:
> mpol_rebind_mm(), which can be called from cpuset_attach(), does down_write(mm->mmap_sem).
> This means down_write(mm->mmap_sem) can be called under cgroup_mutex.
> 
> OTOH, page fault path does down_read(mm->mmap_sem) and calls mem_cgroup_try_charge_xxx(),
> which may eventually calls mem_cgroup_out_of_memory(). And mem_cgroup_out_of_memory()
> calls cgroup_lock().
> This means cgroup_lock() can be called under down_read(mm->mmap_sem).
> 
> If those two paths race, dead lock can happen.
> 
> This patch avoid this dead lock by:
>   - remove cgroup_lock() from mem_cgroup_out_of_memory().
>   - define new mutex (memcg_tasklist) and serialize mem_cgroup_move_task()
>     (->attach handler of memory cgroup) and mem_cgroup_out_of_memory.
> 
> Signed-off-by: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>
> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxx,com>
Ooops, Kamezawa-san's address was invalid...

Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>


Sorry.
Daisuke Nishimura.

> Acked-by: Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx>
> ---
>  mm/memcontrol.c |    5 +++++
>  mm/oom_kill.c   |    2 --
>  2 files changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 9877b03..fec4fc3 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -51,6 +51,7 @@ static int really_do_swap_account __initdata = 1; /* for remember boot option*/
>  #define do_swap_account		(0)
>  #endif
>  
> +static DEFINE_MUTEX(memcg_tasklist);	/* can be hold under cgroup_mutex */
>  
>  /*
>   * Statistics for memory cgroup.
> @@ -797,7 +798,9 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
>  
>  		if (!nr_retries--) {
>  			if (oom) {
> +				mutex_lock(&memcg_tasklist);
>  				mem_cgroup_out_of_memory(mem_over_limit, gfp_mask);
> +				mutex_unlock(&memcg_tasklist);
>  				mem_over_limit->last_oom_jiffies = jiffies;
>  			}
>  			goto nomem;
> @@ -2173,10 +2176,12 @@ static void mem_cgroup_move_task(struct cgroup_subsys *ss,
>  				struct cgroup *old_cont,
>  				struct task_struct *p)
>  {
> +	mutex_lock(&memcg_tasklist);
>  	/*
>  	 * FIXME: It's better to move charges of this process from old
>  	 * memcg to new memcg. But it's just on TODO-List now.
>  	 */
> +	mutex_unlock(&memcg_tasklist);
>  }
>  
>  struct cgroup_subsys mem_cgroup_subsys = {
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index fd150e3..40ba050 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -429,7 +429,6 @@ void mem_cgroup_out_of_memory(struct mem_cgroup *mem, gfp_t gfp_mask)
>  	unsigned long points = 0;
>  	struct task_struct *p;
>  
> -	cgroup_lock();
>  	read_lock(&tasklist_lock);
>  retry:
>  	p = select_bad_process(&points, mem);
> @@ -444,7 +443,6 @@ retry:
>  		goto retry;
>  out:
>  	read_unlock(&tasklist_lock);
> -	cgroup_unlock();
>  }
>  #endif
>  
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