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

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Message-ID: <46F2A8F6.4080508@fr.ibm.com>
Date:	Thu, 20 Sep 2007 19:08:06 +0200
From:	Cedric Le Goater <clg@...ibm.com>
To:	Cedric Le Goater <clg@...ibm.com>
CC:	Pavel Emelyanov <xemul@...nvz.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, "Serge E. Hallyn" <serue@...ibm.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Oleg Nesterov <oleg@...sign.ru>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: 2.6.23-rc6-mm1 - make access to tasks nsproxy ligther (fix)

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@...ibm.com>
Cc: Serge E. Hallyn <serue@...ibm.com>
Cc: Pavel Emelyanov <xemul@...nvz.org>
Cc: Eric W. Biederman <ebiederm@...ssion.com>
Cc: Oleg Nesterov <oleg@...sign.ru>
Cc: Paul E. McKenney <paulmck@...ux.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
-
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