On 08/10, Oleg Nesterov wrote:
>
> On 08/10, Serge E. Hallyn wrote:
> >
> > Quoting Pavel Emelyanov ([EMAIL PROTECTED]):
> > > +/*
> > > + * the namespaces access rules are:
> > > + *
> > > + * 1. only current task is allowed to change tsk->nsproxy pointer or
> > > + * any pointer on the nsproxy itself
> > > + *
> > > + * 2. when accessing (i.e. reading) current task's namespaces - no
> > > + * precautions should be taken - just dereference the pointers
> > > + *
> > > + * 3. the access to other task namespaces is performed like this
> > > + * rcu_read_lock();
> > > + * nsproxy = task_nsproxy(tsk);
> > > + * if (nsproxy != NULL) {
> > > + * / *
> > > + * * work with the namespaces here
> > > + * * e.g. get the reference on one of them
> > > + * * /
> > > + * } / *
> > > + * * NULL task_nsproxy() means that this task is
> > > + * * almost dead (zombie)
> > > + * * /
> > > + * rcu_read_unlock();
> >
> > And lastly, I guess that the caller to switch_task_namespaces() has
> > to ensure that new_nsproxy either (1) is the init namespace, (2) is a
> > brand-new namespace to which noone else has a reference, or (3) the
> > caller has to hold a reference to the new_nsproxy across the call to
> > switch_task_namespaces().
> >
> > As it happens the current calls fit (1) or (2). Again if we happen to
> > jump into the game of switching a task into another task's nsproxy,
> > we'll need to be mindful of (3) so that new_nsproxy can't be tossed into
> > the bin between
> >
> > if (new)
> > get_nsproxy(new);
>
> 4) Unless tsk == current, get_task_namespaces(tsk) and get_nsproxy(tsk)
> are racy even if done under rcu_read_lock().
(sorry for noise, but I'm afraid I was not clear again...)
This looks OK, we don't do get_nsproxy(not_a_current), but perhaps it is
not immediately obvious that we shouldn't.
Oleg.
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