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Re: [ckrm-tech] [PATCH 1/7] containers (V7): Generic container system abstracted from cpusets code [message #11473 is a reply to message #11472]

Sun, 25 March 2007 02:21

Srivatsa Vaddagiri
Messages: 241
Registered: August 2006

Senior Member

On Sat, Mar 24, 2007 at 06:41:28PM -0700, Paul Jackson wrote:
> > the following code becomes racy with cpuset_exit() ...
> >
> > atomic_inc(&cs->count);
> > rcu_assign_pointer(tsk->cpuset, cs);
> > task_unlock(tsk);
>
> eh ... so ... ?
>
> I don't know of any sequence where that causes any problem.
>
> Do you see one?

Let's say we had two cpusets CS1 amd CS2 (both different from top_cpuset).
CS1 has just one task T1 in it (CS1->count = 0) while CS2 has no tasks
in it (CS2->count = 0).

Now consider:

------------------------------------------------------------ --------
CPU0 (attach_task T1 to CS2) CPU1 (T1 is exiting)
------------------------------------------------------------ --------

task_lock(T1);

oldcs = tsk->cpuset;
[oldcs = CS1]

T1->flags & PF_EXITING? (No)

T1->flags = PF_EXITING;

atomic_inc(&CS2->count);

cpuset_exit()
cs = tsk->cpuset; (cs = CS1)

T1->cpuset = CS2;

T1->cpuset = &top_cpuset;

task_unlock(T1);

CS2 has one bogus count now (with no tasks in it), which may prevent it from
being removed/freed forever.

Not just this, continuing further we have more trouble:

------------------------------------------------------------ --------
CPU0 (attach_task T1 to CS2) CPU1 (T1 is exiting)
------------------------------------------------------------ --------

synchronize_rcu()
atomic_dec(&CS1->count);
[CS1->count = 0]

if atomic_dec_and_test(&oldcs->count))
[CS1->count = -1]

We now have CS1->count negative. Is that good? I am uncomfortable ..

We need a task_lock() in cpuset_exit to avoid this race.

--
Regards,
vatsa

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[Message index]

		[PATCH 0/7] containers (V7): Generic Process Containers By: Paul Menage on Mon, 12 February 2007 08:15
		[PATCH 2/7] containers (V7): Cpusets hooked into containers By: Paul Menage on Mon, 12 February 2007 08:15
		Re: [PATCH 2/7] containers (V7): Cpusets hooked into containers By: Paul Menage on Thu, 15 February 2007 20:49
		Re: [PATCH 2/7] containers (V7): Cpusets hooked into containers By: serue on Thu, 15 February 2007 20:35
		Re: [PATCH 2/7] containers (V7): Cpusets hooked into containers By: Srivatsa Vaddagiri on Wed, 07 March 2007 14:34
		Re: [PATCH 2/7] containers (V7): Cpusets hooked into containers By: Paul Menage on Wed, 07 March 2007 16:01
		Re: [ckrm-tech] [PATCH 2/7] containers (V7): Cpusets hooked into containers By: Srivatsa Vaddagiri on Wed, 07 March 2007 16:24
		Re: [ckrm-tech] [PATCH 2/7] containers (V7): Cpusets hooked into containers By: Paul Menage on Wed, 07 March 2007 16:31
		Re: [PATCH 2/7] containers (V7): Cpusets hooked into containers By: Srivatsa Vaddagiri on Wed, 07 March 2007 14:52
		Re: [PATCH 2/7] containers (V7): Cpusets hooked into containers By: Paul Menage on Wed, 07 March 2007 16:12
		[PATCH 4/7] containers (V7): Simple CPU accounting container subsystem By: Paul Menage on Mon, 12 February 2007 08:15
		[PATCH 7/7] containers (V7): Container interface to nsproxy subsystem By: Paul Menage on Mon, 12 February 2007 08:15
		Re: [ckrm-tech] [PATCH 7/7] containers (V7): Container interface to nsproxy subsystem By: Srivatsa Vaddagiri on Sat, 24 March 2007 04:58
		Re: [ckrm-tech] [PATCH 7/7] containers (V7): Container interface to nsproxy subsystem By: serue on Mon, 26 March 2007 21:55
		Re: [ckrm-tech] [PATCH 7/7] containers (V7): Container interface to nsproxy subsystem By: Srivatsa Vaddagiri on Sat, 24 March 2007 16:23
		Re: [ckrm-tech] [PATCH 7/7] containers (V7): Container interface to nsproxy subsystem By: serue on Mon, 26 March 2007 21:57
		Re: [ckrm-tech] [PATCH 7/7] containers (V7): Container interface to nsproxy subsystem By: Srivatsa Vaddagiri on Wed, 28 March 2007 14:55
		Re: [ckrm-tech] [PATCH 7/7] containers (V7): Container interface to nsproxy subsystem By: Srivatsa Vaddagiri on Sat, 31 March 2007 02:47
		Re: [ckrm-tech] [PATCH 7/7] containers (V7): Container interface to nsproxy subsystem By: serue on Mon, 02 April 2007 14:09
		[PATCH 6/7] containers (V7): BeanCounters over generic process containers By: Paul Menage on Mon, 12 February 2007 08:15
		Re: [PATCH 6/7] containers (V7): BeanCounters over generic process containers By: Srivatsa Vaddagiri on Mon, 12 February 2007 15:34
		Re: [PATCH 6/7] containers (V7): BeanCounters over generic process containers By: Paul Menage on Mon, 12 February 2007 18:49
		Re: [PATCH 6/7] containers (V7): BeanCounters over generic process containers By: xemul on Tue, 13 February 2007 08:52
		Re: [PATCH 6/7] containers (V7): BeanCounters over generic process containers By: Paul Menage on Tue, 13 February 2007 09:03
		Re: [PATCH 6/7] containers (V7): BeanCounters over generic process containers By: xemul on Tue, 13 February 2007 09:18
		Re: [PATCH 6/7] containers (V7): BeanCounters over generic process containers By: Paul Menage on Tue, 13 February 2007 09:37
		Re: [PATCH 6/7] containers (V7): BeanCounters over generic process containers By: xemul on Tue, 13 February 2007 09:49
		Re: [PATCH 6/7] containers (V7): BeanCounters over generic process containers By: Paul Menage on Thu, 15 February 2007 00:47
		[PATCH 5/7] containers (V7): Resource Groups over generic containers By: Paul Menage on Mon, 12 February 2007 08:15
		[PATCH 1/7] containers (V7): Generic container system abstracted from cpusets code By: Paul Menage on Mon, 12 February 2007 08:15
		Re: [PATCH 1/7] containers (V7): Generic container system abstracted from cpusets code By: Paul Menage on Mon, 12 February 2007 19:26
		Re: [PATCH 1/7] containers (V7): Generic container system abstracted from cpusets code By: Paul Menage on Mon, 12 February 2007 19:46
		Re: [PATCH 1/7] containers (V7): Generic container system abstracted from cpusets code By: Srivatsa Vaddagiri on Tue, 13 February 2007 05:48
		Re: [ckrm-tech] [PATCH 1/7] containers (V7): Generic container system abstracted from cpusets code By: Srivatsa Vaddagiri on Tue, 13 February 2007 08:16
		Re: [PATCH 1/7] containers (V7): Generic container system abstracted from cpusets code By: Srivatsa Vaddagiri on Wed, 07 March 2007 12:21
		Re: [ckrm-tech] [PATCH 1/7] containers (V7): Generic container system abstracted from cpusets code By: Srivatsa Vaddagiri on Wed, 07 March 2007 14:06
		Re: [PATCH 1/7] containers (V7): Generic container system abstracted from cpusets code By: Paul Menage on Wed, 07 March 2007 20:50
		Re: [ckrm-tech] [PATCH 1/7] containers (V7): Generic container system abstracted from cpusets code By: Srivatsa Vaddagiri on Thu, 08 March 2007 10:31
		Re: [ckrm-tech] [PATCH 1/7] containers (V7): Generic container system abstracted from cpusets code By: Paul Menage on Thu, 08 March 2007 10:40
		Re: [ckrm-tech] [PATCH 1/7] containers (V7): Generic container system abstracted from cpusets code By: Paul Jackson on Sun, 11 March 2007 19:38
		Re: [ckrm-tech] [PATCH 1/7] containers (V7): Generic container system abstracted from cpusets code By: Srivatsa Vaddagiri on Mon, 12 March 2007 14:19
		Re: [ckrm-tech] [PATCH 1/7] containers (V7): Generic container system abstracted from cpusets code By: Srivatsa Vaddagiri on Thu, 22 March 2007 09:56
		Re: [ckrm-tech] [PATCH 1/7] containers (V7): Generic container system abstracted from cpusets code By: Srivatsa Vaddagiri on Thu, 22 March 2007 10:20
		Re: [ckrm-tech] [PATCH 1/7] containers (V7): Generic container system abstracted from cpusets code By: Srivatsa Vaddagiri on Sat, 24 March 2007 14:58
		Re: [ckrm-tech] [PATCH 1/7] containers (V7): Generic container system abstracted from cpusets code By: Paul Jackson on Sat, 24 March 2007 19:25
		Re: [ckrm-tech] [PATCH 1/7] containers (V7): Generic container system abstracted from cpusets code By: Srivatsa Vaddagiri on Sun, 25 March 2007 00:38
		Re: [ckrm-tech] [PATCH 1/7] containers (V7): Generic container system abstracted from cpusets code By: Paul Jackson on Sun, 25 March 2007 01:41
		Re: [ckrm-tech] [PATCH 1/7] containers (V7): Generic container system abstracted from cpusets code By: Srivatsa Vaddagiri on Sun, 25 March 2007 02:21
		Re: [ckrm-tech] [PATCH 1/7] containers (V7): Generic container system abstracted from cpusets code By: Srivatsa Vaddagiri on Sun, 25 March 2007 04:16
		Re: [ckrm-tech] [PATCH 1/7] containers (V7): Generic container system abstracted from cpusets code By: Paul Jackson on Sun, 25 March 2007 05:43
		Re: [ckrm-tech] [PATCH 1/7] containers (V7): Generic container system abstracted from cpusets code By: Srivatsa Vaddagiri on Sun, 25 March 2007 08:14
		Re: [ckrm-tech] [PATCH 1/7] containers (V7): Generic container system abstracted from cpusets code By: Paul Jackson on Sun, 25 March 2007 04:45
		Re: [ckrm-tech] [PATCH 1/7] containers (V7): Generic container system abstracted from cpusets code By: Srivatsa Vaddagiri on Sun, 25 March 2007 04:57
		Re: [ckrm-tech] [PATCH 1/7] containers (V7): Generic container system abstracted from cpusets code By: Paul Jackson on Sun, 25 March 2007 04:59
		Re: [PATCH 0/7] containers (V7): Generic Process Containers By: Paul Jackson on Mon, 12 February 2007 09:18
		Re: [PATCH 0/7] containers (V7): Generic Process Containers By: Paul Menage on Mon, 12 February 2007 09:32
		Re: [PATCH 0/7] containers (V7): Generic Process Containers By: Paul Jackson on Mon, 12 February 2007 09:52
		[PATCH 3/7] containers (V7): Add generic multi-subsystem API to containers By: Paul Menage on Mon, 12 February 2007 08:15
		Re: [PATCH 3/7] containers (V7): Add generic multi-subsystem API to containers By: Paul Menage on Mon, 12 February 2007 18:31
		Re: [PATCH 3/7] containers (V7): Add generic multi-subsystem API to containers By: Cedric Le Goater on Mon, 12 February 2007 15:56
		Re: [PATCH 3/7] containers (V7): Add generic multi-subsystem API to containers By: Balbir Singh on Wed, 14 February 2007 08:49
		Re: [PATCH 0/7] containers (V7): Generic Process Containers By: Paul Menage on Mon, 12 February 2007 23:15
		Re: [PATCH 0/7] containers (V7): Generic Process Containers By: Sam Vilain on Tue, 13 February 2007 00:30
		Re: [PATCH 0/7] containers (V7): Generic Process Containers By: ebiederm on Tue, 20 February 2007 17:34
		Re: [PATCH 0/7] containers (V7): Generic Process Containers By: Paul Menage on Mon, 12 February 2007 23:18
		Re: [PATCH 0/7] containers (V7): Generic Process Containers By: serue on Mon, 12 February 2007 22:47
		Re: [PATCH 0/7] containers (V7): Generic Process Containers By: Sam Vilain on Mon, 12 February 2007 22:38
		Re: [PATCH 0/7] containers (V7): Generic Process Containers By: Paul Menage on Tue, 20 February 2007 17:55
		Re: [PATCH 0/7] containers (V7): Generic Process Containers By: ebiederm on Tue, 20 February 2007 19:29
		Re: [PATCH 0/7] containers (V7): Generic Process Containers By: Paul Menage on Tue, 20 February 2007 22:47
		Re: [PATCH 0/7] containers (V7): Generic Process Containers By: serue on Tue, 20 February 2007 23:32
		Re: [PATCH 0/7] containers (V7): Generic Process Containers By: Sam Vilain on Tue, 20 February 2007 23:08
		Re: [PATCH 0/7] containers (V7): Generic Process Containers By: Sam Vilain on Tue, 20 February 2007 21:58
		Re: [PATCH 0/7] containers (V7): Generic Process Containers By: Paul Menage on Tue, 20 February 2007 22:19
		Re: [PATCH 0/7] containers (V7): Generic Process Containers By: Sam Vilain on Tue, 20 February 2007 22:58
		Re: [PATCH 0/7] containers (V7): Generic Process Containers By: Paul Menage on Tue, 20 February 2007 23:28
		Re: [PATCH 0/7] containers (V7): Generic Process Containers By: Paul Menage on Tue, 20 February 2007 23:36
		Re: [PATCH 0/7] containers (V7): Generic Process Containers By: serue on Tue, 20 February 2007 23:37

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