Re: [Experimental][PATCH 19/21] memcg-fix-pre-destroy.patch

[Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>]

Added CC: Paul Menage <menage@google.com>

> @@ -2096,7 +2112,7 @@ static void mem_cgroup_get(struct mem_cg
>  static void mem_cgroup_put(struct mem_cgroup *mem)
>  {
>  	if (atomic_dec_and_test(&mem->refcnt)) {
> -		if (!mem->obsolete)
> +		if (!css_under_removal(&mem->css))
>  			return;
>  		mem_cgroup_free(mem);
>  	}
I don't think it's safe to check css_under_removal here w/o cgroup_lock.
(It's safe *NOW* just because memcg is the only user of css->refcnt.)

As Li said before, css_under_removal doesn't necessarily mean
this this group has been destroyed, but mem_cgroup will be freed.

But adding cgroup_lock/unlock here causes another dead lock,
because mem_cgroup_get_next_node calls mem_cgroup_put.

hmm.. hierarchical reclaim code will be re-written completely by [21/21],
so would it be better to change patch order or to take another approach ?


Thanks,
Daisuke Nishimura.

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