Re: 2.6.23-rc6-mm1 - make access to tasks nsproxy ligther (fix)

Cedric Le Goater
2007-09-20T17:08:19Z

Cedric Le Goater wrote:
> Pavel Emelyanov wrote:
>> Looks sane :)
>>
>> [snip]
>>
>>> Index: 2.6.23-rc6-mm1/kernel/exit.c
>>> ===================================================================
>>> --- 2.6.23-rc6-mm1.orig/kernel/exit.c
>>> +++ 2.6.23-rc6-mm1/kernel/exit.c
>>> @@ -408,6 +408,8 @@ void daemonize(const char *name, ...)
>>> current->fs = fs;
>>> atomic_inc(&fs->count);
>>>
>>> + if (current->nsproxy != init_task.nsproxy)
>>> + get_nsproxy(init_task.nsproxy);
>>> switch_task_namespaces(current, init_task.nsproxy);
>> shouldn't we make the switch under this if() as well?
>
> right. we can probably simplify switch_task_namespaces() and remove :
>
> if (ns == new)
> return;
>
> I'll cook a better one today.

So I removed this test in

* daemonize() bc it is already done
* sys_unshare() bc the nsproxy is always new one
* exit_task_namespaces() bc it is called with NULL and the
task will die right after that.

C.

make-access-to-tasks-nsproxy-lighter.patch breaks unshare()

when called from unshare(), switch_task_namespaces() takes an
extra refcount on the nsproxy, leading to a memory leak of
nsproxy objects.

Now the problem is that we still need that extra ref when called
from daemonize(). Here's an ugly fix for it.

Signed-off-by: Cedric Le Goater <clg@fr.ibm.com>
Cc: Serge E. Hallyn <serue@us.ibm.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

---
include/linux/nsproxy.h | 5 +++++
kernel/exit.c | 5 ++++-
kernel/nsproxy.c | 9 ---------
3 files changed, 9 insertions(+), 10 deletions(-)

Index: 2.6.23-rc6-mm1/kernel/nsproxy.c
===================================================================
--- 2.6.23-rc6-mm1.orig/kernel/nsproxy.c
+++ 2.6.23-rc6-mm1/kernel/nsproxy.c
@@ -25,11 +25,6 @@ static struct kmem_cache *nsproxy_cachep

struct nsproxy init_nsproxy = INIT_NSPROXY(init_nsproxy);

-static inline void get_nsproxy(struct nsproxy *ns)
-{
- atomic_inc(&ns->count);
-}
-
/*
* creates a copy of "orig" with refcount 1.
*/
@@ -205,11 +200,7 @@ void switch_task_namespaces(struct task_
might_sleep();

ns = p->nsproxy;
- if (ns == new)
- return;

- if (new)
- get_nsproxy(new);
rcu_assign_pointer(p->nsproxy, new);

if (ns && atomic_dec_and_test(&ns->count)) {
Index: 2.6.23-rc6-mm1/kernel/exit.c
===================================================================
--- 2.6.23-rc6-mm1.orig/kernel/exit.c
+++ 2.6.23-rc6-mm1/kernel/exit.c
@@ -408,7 +408,10 @@ void daemonize(const char *name, ...)
current->fs = fs;
atomic_inc(&fs->count);

- switch_task_namespaces(current, init_task.nsproxy);
+ if (current->nsproxy != init_task.nsproxy) {
+ get_nsproxy(init_task.nsproxy);
+ switch_task_namespaces(current, init_task.nsproxy);
+ }

exit_files(current);
current->files = init_task.files;
Index: 2.6.23-rc6-mm1/include/linux/nsproxy.h
===================================================================
--- 2.6.23-rc6-mm1.orig/include/linux/nsproxy.h
+++ 2.6.23-rc6-mm1/include/linux/nsproxy.h
@@ -77,6 +77,11 @@ static inline void put_nsproxy(struct ns
}
}

+static inline void get_nsproxy(struct nsproxy *ns)
+{
+ atomic_inc(&ns->count);
+}
+
#ifdef CONFIG_CONTAINER_NS
int ns_container_clone(struct task_struct *tsk);
#else