[Devel] Re: - merge-sys_clone-sys_unshare-nsproxy-and-namespace.patch removed from -mm tree

[Herbert Poetzl]

On Mon, Jun 18, 2007 at 02:37:25PM +0200, Cedric Le Goater wrote:
> Herbert Poetzl wrote:
> > On Sun, Jun 17, 2007 at 06:38:30PM +0400, Oleg Nesterov wrote:
> >> On 06/16, Herbert Poetzl wrote:
> >>> On Tue, May 08, 2007 at 07:45:35PM -0700, akpm at linux-foundation.org wrote:
> >>>> The patch titled
> >>>>      Merge sys_clone()/sys_unshare() nsproxy and namespace handling
> >>>> has been removed from the -mm tree.  Its filename was
> >>>>      merge-sys_clone-sys_unshare-nsproxy-and-namespace.patch
> >>>>
> >>>> This patch was dropped because it was merged into mainline or a subsystem tree
> >>>>
> >>> .. [zapped] ...
> >>>
> >>>> + * Called from unshare. Unshare all the namespaces part of nsproxy.
> >>>> + * On sucess, returns the new nsproxy and a reference to old nsproxy
> >>>> + * to make sure it stays around.
> >>>> + */
> >>>> +int unshare_nsproxy_namespaces(unsigned long unshare_flags,
> >>>> +		struct nsproxy **new_nsp, struct fs_struct *new_fs)
> >>>> +{
> >>> this makes sys_unshare leak and nsproxy (reference)
> >>>
> >>> can be tested with the following command sequence:
> >>>    vcmd -nu ^17 -- vcmd -nu ^17 -- sleep 10
> >> I know almost nothing about this stuff, could you please explain in
> >> brief what this command does ...
> > 
> > yeah, sure, it basically calls sys_unshare() with
> > bit 17 (CLONE_NEWNS) set then invokes the chained
> > command, so we get a sleep which is in a separate
> > namespace, unshared from a namespace != the main
> > one ...
> > 
> >> ... and how do you detect a leak?
> > 
> >>> (and some nsproxy accounting/debugging as used in
> >>>  Linux-VServer)
> > 
> > on Linux-VServer,we have accounting for those
> > proxies (and several other namespace related stuff)
> > because we already suspected leakage and reference
> > bugs in this area some time ago ... btw, I also
> > suggested to put a similar functionality in mainline
> > for the time being, but it was ignored, as usual ...
> > 
> >>> we probably want to drop the reference to the old
> >>> nsproxy in sys_unshare() but I do not see a good reason
> >>> to take the reference in the first place (at least not
> >>> with the code in mainline 2.6.22-rc4)
> >> At first glance, sys_unshare() drops the reference to 
> >> the old nsproxy,
> > 
> > okay, the 'current' task has an nsproxy, and keeps
> > a reference to that (let's assume it is the only
> > task using this nsproxy, then the count will be 1)
> > 
> > unshare_nsproxy_namespaces() now does get_nsproxy()
> > which makes the count=2, then it creates a new
> > nsproxy (which will get count=1), and returns ...
> > 
> >> 		old_nsproxy = current->nsproxy;
> >> 		current->nsproxy = new_nsproxy;
> >> 		new_nsproxy = old_nsproxy;
> > 
> > sys_unshare, now replaces the current->nsproxy with
> > the new one, which will have the correct count=1,
> > and puts the old nsproxy (which has count=2), and
> > thus the nsproxy will not get released, although
> > it isn't referenced/used anymore ...
> 
> 
> Herbert,
> 
> Could you give a try to the patch i've sent previously 
> and this one which removes an extra get_nsproxy() ? 

will do so shortly ...

> It fixes the leak for me. I've run the ltp tests we 
> have on namespace unsharing and i could see the no 
> leaks in /proc/slabinfo.

> Badari,
> 
> That extra get_nsproxy() seemed a superfluous remain 
> from the 2.6.20. 
> Do you see any issues with it ?
> 
> If we're all happy with these fixes, i'll send them on 
> lkml@ for review. 

I'm not terribly happy with the current nsproxy
framework, although it improved somewhat ...

I'm still missing some mechanism to 'mix' two
proxies according to a flagmask (which is required
to enter a guest 'partially') ...

best,
Herbert

> They might deserve to be in 2.6.22.
> 
> Thanks,
> 
> C. 
> 
> Signed-off-by: Cedric Le Goater <clg at fr.ibm.com>
> ---
>  kernel/nsproxy.c |    7 +------
>  1 file changed, 1 insertion(+), 6 deletions(-)
> 
> Index: 2.6.22-rc4-mm2/kernel/nsproxy.c
> ===================================================================
> --- 2.6.22-rc4-mm2.orig/kernel/nsproxy.c
> +++ 2.6.22-rc4-mm2/kernel/nsproxy.c
> @@ -175,7 +175,6 @@ void free_nsproxy(struct nsproxy *ns)
>  int unshare_nsproxy_namespaces(unsigned long unshare_flags,
>                 struct nsproxy **new_nsp, struct fs_struct *new_fs)
>  {
> -       struct nsproxy *old_ns = current->nsproxy;
>         int err = 0;
>  
>         if (!(unshare_flags & (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC |
> @@ -185,14 +184,10 @@ int unshare_nsproxy_namespaces(unsigned 
>         if (!capable(CAP_SYS_ADMIN))
>                 return -EPERM;
>  
> -       get_nsproxy(old_ns);
> -
>         *new_nsp = create_new_namespaces(unshare_flags, current,
>                                 new_fs ? new_fs : current->fs);
> -       if (IS_ERR(*new_nsp)) {
> +       if (IS_ERR(*new_nsp))
>                 err = PTR_ERR(*new_nsp);
> -               put_nsproxy(old_ns);
> -       }
>         return err;
>  }
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