linux-kernel - Re: [PATCH 2/4] freezer_cg: remove redundant check in freezer_can

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 21 Oct 2008 11:47:40 +0200
From:	Cedric Le Goater <clg@...ibm.com>
To:	Li Zefan <lizf@...fujitsu.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Containers <containers@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/4] freezer_cg: remove redundant check in freezer_can_attach()

Li Zefan wrote:
> Cedric Le Goater wrote:
>> Li Zefan wrote:
>>> It is sufficient to check if @task is frozen, and no need to check if
>>> the original freezer is frozen.
>> hmm, a task being frozen does not mean that its freezer cgroup is 
>> frozen.
> 
> If a task has being frozen, then can_attach() returns -EBUSY at once.
> If a task isn't frozen, then we have orig_freezer->state == THAWED.
> 
> So we need to check the state of the task only.
> 
>> So the extra check seems valid but looking at the comment :
>>
>> 	/*
>> 	 * The call to cgroup_lock() in the freezer.state write method prevents
>> 	 * a write to that file racing against an attach, and hence the
>> 	 * can_attach() result will remain valid until the attach completes.
>> 	 */
>> 	static int freezer_can_attach(struct cgroup_subsys *ss,
>>
>> how do we know that the task_freezer(task), which is not protected by
>> the cgroup_lock(), is not going to change its state to CGROUP_FROZEN 
>> it looks racy.
>>
> 
> Since freezer_can_attach() is called by cgroup core with cgroup_lock held, there is
> no race with task attaching and state changing.

ok I see. cgroup_mutex is global, I thought it had changed and that we 
were only locking the cgroup the task was being attached to. 

Acked-by: Cedric Le Goater <clg@...ibm.com>

thanks,

C. 

 
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/