netdev - Re: [PATCH 06/21] nfs client: exit

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Date:   Sun, 5 Nov 2017 18:55:42 +0000
From:   Trond Myklebust <trondmy@...marydata.com>
To:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "vvs@...tuozzo.com" <vvs@...tuozzo.com>
CC:     "anna.schumaker@...app.com" <anna.schumaker@...app.com>,
        "linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>
Subject: Re: [PATCH 06/21] nfs client: exit_net cleanup check added

On Sun, 2017-11-05 at 19:48 +0300, Vasily Averin wrote:
> On 2017-11-05 19:02, Trond Myklebust wrote:
> > On Sun, 2017-11-05 at 13:00 +0300, Vasily Averin wrote:
> > > Be sure that nfs_client_list and nfs_volume_list lists
> > > initialized
> > > in net_init hook were return to initial state in net_exit hook.
> > > 
> > > Signed-off-by: Vasily Averin <vvs@...tuozzo.com>
> > > ---
> > >  fs/nfs/client.c | 4 ++++
> > >  1 file changed, 4 insertions(+)
> > > 
> > > diff --git a/fs/nfs/client.c b/fs/nfs/client.c
> > > index 22880ef..7c0691c 100644
> > > --- a/fs/nfs/client.c
> > > +++ b/fs/nfs/client.c
> > > @@ -204,6 +204,10 @@ void nfs_cleanup_cb_ident_idr(struct net
> > > *net)
> > >  	struct nfs_net *nn = net_generic(net, nfs_net_id);
> > >  
> > >  	idr_destroy(&nn->cb_ident_idr);
> > > +	WARN(!list_empty(&nn->nfs_client_list),
> > > +	     "net %p exit: nfs_client_list is not empty\n",
> > > net);
> > > +	WARN(!list_empty(&nn->nfs_volume_list),
> > > +	     "net %p exit: nfs_volume_list is not empty\n",
> > > net);
> > >  }
> > >  
> > 
> > Why do we need these? Is there a specific bug that you are trying
> > to
> > track down?
> 
> I hope such checks allows to detect leaked per-netns objects.
> Also I hope that all new pernet_operations will inherit such checks
> too.
> 
> I assume that elements added into per-net lists should not live
> longer than net namespace,
> and should be deleted from the list. I think exit_net hook is good
> place for such check.
> 
> Recently I've found lost list_entry and enabled timer on stop of net
> namespace.
> Then I've reviewed all existing pernet_operations and found that many
> drivers
> have such checks already. So I decided to complete this task and add
> such checks
> into all affected subsystems.
> 

Unless there is a known problem that has specific debugging needs, this
kind of assert should take the form of a WARN_ONCE() so that it doesn't
fill user syslogs with redundant warnings if triggered.

-- 
Trond Myklebust
Linux NFS client maintainer, PrimaryData
trond.myklebust@...marydata.com