Re: [RFC][PATCH] Make access to taks's nsproxy liter

[Pavel Emelyanov <xemul-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org>]

Eric W. Biederman wrote:
> Pavel Emelyanov <xemul-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org> writes:
> 
>> Eric W. Biederman wrote:
>>> Pavel Emelyanov <xemul-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org> writes:
>>>
>>>> When someone wants to deal with some other taks's namespaces
>>>> it has to lock the task and then to get the desired namespace
>>>> if the one exists. This is slow on read-only paths and may be
>>>> impossible in some cases.
>>>>
>>>> E.g. Oleg recently noticed a race between unshare() and the
>>>> (just sent for review) pid namespaces - when the task notifies
>>>> the parent it has to know the parent's namespace, but taking
>>>> the task_lock() is impossible there - the code is under write
>>>> locked tasklist lock.
>>>>
>>>> On the other hand switching the namespace on task (daemonize)
>>>> and releasing the namespace (after the last task exit) is rather
>>>> rare operation and we can sacrifice its speed to solve the
>>>> issues above.
>>>
>>> Looks pretty decent but we need to clearly say what lock
>>> you have to have to assign to the nsproxy pointer.
>> no locks - only current is allowed to change its nsproxy!
> 
> Exactly.  Just need a comment or something to make that clear.

Oh! Ok, I will add it. Thanks.

> Eric
>