[Devel] Re: [PATCH 1/15] Move exit_task_namespaces()

[Kirill Korotaev]

Oleg Nesterov wrote:
> On 07/26, Pavel Emelyanov wrote:
> 
>>Make task release its namespaces after it has reparented all his
>>children to child_reaper, but before it notifies its parent about
>>its death.
>>
>>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.
>>
>>The reason to release namespace before notifying the parent it that
>>when task sends a SIGCHLD to parent it can call wait() on this taks
>>and release it. But releasing the mnt namespace implies dropping
>>of all the mounts in the mnt namespace and NFS expects the task to
>>have valid sighand pointer.
>>
>>Signed-off-by: Pavel Emelyanov <xemul at openvz.org>
>>
>>---
>>
>>exit.c |    5 ++++-
>>1 files changed, 4 insertions(+), 1 deletion(-)
>>
>>diff -upr linux-2.6.23-rc1-mm1.orig/kernel/exit.c 
>>linux-2.6.23-rc1-mm1-7/kernel/exit.c
>>--- linux-2.6.23-rc1-mm1.orig/kernel/exit.c	2007-07-26 
>>16:34:45.000000000 +0400
>>+++ linux-2.6.23-rc1-mm1-7/kernel/exit.c	2007-07-26 
>>16:36:37.000000000 +0400
>>@@ -788,6 +804,10 @@ static void exit_notify(struct task_stru
>>	BUG_ON(!list_empty(&tsk->children));
>>	BUG_ON(!list_empty(&tsk->ptrace_children));
>>
>>+	write_unlock_irq(&tasklist_lock);
>>+	exit_task_namespaces(tsk);
>>+	write_lock_irq(&tasklist_lock);
> 
> 
> No.
> 
> We "cleared" our ->children/->ptrace_children lists. Now suppose that
> another thread dies, and its forget_original_parent() choose us as a
> new reaper before we re-take tasklist.
> 
> I'll try to read other patches tomorrow, but I can't avoid a stupid
> question: can we have a CONFIG_ for that? This series adds a lot of
> complications.

the was a request from many people including Andrew that CONFIG_XXX
is bad approach.

> OK, I guess the answer is "it is very difficult t achieve", but can't
> help myself :)

First versions of Pavel's patches had CONFIG_XXX for this.

Thanks,
Kirill
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