linux-kernel - Re: [PATCH] TOMOYO: Add garbage collector support. (v2)

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Message-Id: <200906020030.n520UU1D087893@www262.sakura.ne.jp>
Date:	Tue, 02 Jun 2009 09:30:30 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:	serge@...lyn.com
Cc:	serue@...ibm.com, linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] TOMOYO: Add garbage collector support. (v2)

Serge E. Hallyn wrote:
> Can't you just move the deleted item from the live list to some dead
> list, using the same ->list list_head?

I think I can't. If we do list_add(&p->entry.list, &dead_list) after
list_del_rcu(&p->entry.list) when p->entry.users != 0, p->entry.list.next will
point to an element on dead list. And reader will no longer be able to resume
travarsal on the live list.

I don't want the item be deleted from the live list as long as there are
readers (i.e. p->entry.users != 0).

If we use different ->list list_head, reader will be able to resume travarsal
on the live list. (But will use more memory than ->is_deleted.)

struct something {
	struct {
		struct list_head list_for_live_list;
		atomic_t users;
	} entry;
	struct list_head list_for_dead_list;
	int data;
} *p;

Regards.
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