linux-kernel - Re: [RFC][PATCH 2/4] memcg: fix error path of mem_cgroup_move

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Message-ID: <37143.10.75.179.62.1231412446.squirrel@webmail-b.css.fujitsu.com>
Date:	Thu, 8 Jan 2009 20:00:46 +0900 (JST)
From:	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>
To:	"Daisuke Nishimura" <nishimura@....nes.nec.co.jp>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	kamezawa.hiroyu@...fujitsu.com, balbir@...ux.vnet.ibm.com,
	lizf@...fujitsu.com, menage@...gle.com, nishimura@....nes.nec.co.jp
Subject: Re: [RFC][PATCH 2/4] memcg: fix error path of 
     mem_cgroup_move_parent

Daisuke Nishimura said:
> There is a bug in error path of mem_cgroup_move_parent.
>
> Extra refcnt got from try_charge should be dropped, and usages incremented
> by try_charge should be decremented in both error paths:
>
>     A: failure at get_page_unless_zero
>     B: failure at isolate_lru_page
>
> This bug makes this parent directory unremovable.
>
> In case of A, rmdir doesn't return, because res.usage doesn't go
> down to 0 at mem_cgroup_force_empty even after all the pc in
> lru are removed.
> In case of B, rmdir fails and returns -EBUSY, because it has
> extra ref counts even after res.usage goes down to 0.
>
>
> Signed-off-by: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Thank you for catching.

Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>


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