linux-kernel - Re: [ckrm-tech] [PATCH 1/7] containers (V7): Generic container system abstracted from cpusets code

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Date:	Sat, 24 Mar 2007 12:25:59 -0700
From:	Paul Jackson <pj@....com>
To:	vatsa@...ibm.com
Cc:	menage@...gle.com, akpm@...l.org, sekharan@...ibm.com, dev@...ru,
	xemul@...ru, serue@...ibm.com, ebiederm@...ssion.com,
	ckrm-tech@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	containers@...ts.osdl.org, mbligh@...gle.com, winget@...gle.com,
	rohitseth@...gle.com, devel@...nvz.org
Subject: Re: [ckrm-tech] [PATCH 1/7] containers (V7): Generic container
 system abstracted from cpusets code

> IMO, we need to use task_lock() in container_exit() to avoid this race.
> 
> (I think this race already exists in mainline cpuset.c?)
> 
> P.S : cpuset.c checks for PF_EXITING twice in attach_task(), while this
> patch seems to be checking only once. Is that fine?

I think the cpuset code is ok, because, as you note, it locks the task,
picks off the cpuset pointer, and then checks a second time that the
task still does not have PF_EXITING set:

In the kernel/cpuset.c code for attach_task():

        task_lock(tsk);
        oldcs = tsk->cpuset;
        /*
         * After getting 'oldcs' cpuset ptr, be sure still not exiting.
         * If 'oldcs' might be the top_cpuset due to the_top_cpuset_hack
         * then fail this attach_task(), to avoid breaking top_cpuset.count.
         */
        if (tsk->flags & PF_EXITING) {
                task_unlock(tsk);
                mutex_unlock(&callback_mutex);
                put_task_struct(tsk);
                return -ESRCH;
        }

-- 
                  I won't rest till it's the best ...
                  Programmer, Linux Scalability
                  Paul Jackson <pj@....com> 1.925.600.0401
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