Oleg Nesterov wrote:
On 08/06, Pavel Emelyanov wrote:
Oleg Nesterov wrote:
On 08/06, Pavel Emelyanov wrote:
Oleg Nesterov wrote:
On 07/26, Pavel Emelyanov wrote:
The reason to release namespaces after reparenting is that when task
exits it may send a signal to its parent (SIGCHLD), but if the parent
has already exited its namespaces there will be no way to decide what
pid to dever to him - parent can be from different namespace.
I almost forgot about this one...
After reading the whole series, I can't understand the above explanation
any longer. The parent can't be from different namespace, either we have
another sub-thread, or we reparent the child to /sbin/init which should
be from the same namespace.
If the child that is a new namespace's init is exiting its parent is from
the
different namespace.
In that case it doesn't have childs. The were SIGKILL'ed before
exit_notify().
It does not, but it's parent - does :)
Yes. But in that case forget_original_parent() is no-op! This means that
it is not needed to move exit_task_namepsace() after.
Moreover, we will probably want to implement "entering"
the pid namespace, so having tasks with parents from another namespace
will
be OK.
Well. I saw this word "entering", but I don't know the meaning. Just
curious,
could you explain?
"Entering" means "moving task to arbitrary namespace"
Heh. Very much nontrivial, good luck :) At least we need to grow ->numbers[],
and if its pid was pinned...
And, if an exiting task has a child which is already from another
namespace,
why can't we release our namespace before re-parenting? I guess I need to
know what "entering" means to understand this...
One of the desired actions was the following:
1. task X clones the new namespace with the child Y as this namespace's
init;
2. task X waits for SIGCHILD to come informing that the namespace is dead.
In this scenario we need to set the Y's pid as it is seen from X's
namespace in siginfo.
Yes sure. But again, how this is connected to "we should do exit_task_namespace()
after forget_original_parent()" ?
I guess I missed something stupid and simple...
In other words. Let task X live in init_pid_ns, task Y is his child and lives
int another namespace. task X and task Y both die. This will happen:
1. Task X call exit_task_namespaces()
and sets its nsproxy to NULL
1. Task Y is going to notify the
parent (X) and dereferences its
nsproxy -> OOPS
2. Task X reparents all its children
If we move the exit_task_namespace this will happen:
1. Task X reparents all its children
2. Task X call exit_task_namespaces()
and sets its nsproxy to NULL
In such case is tasy Y will dereference the parent's nsproxy it will not
OOPS because either its parent will be not X already, or X's nsproxy is
not yet released.
Oleg.
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