Re: [PATCH v3 2/4] SUNRPC: fix races on PipeFS UMOUNT notifications

[Stanislav Kinsbursky]

25.06.2013 20:13, Myklebust, Trond ÐÐÑÐÑ:
> On Mon, 2013-06-24 at 11:52 +0400, Stanislav Kinsbursky wrote:
> > CPU#0                                   CPU#1
> > -----------------------------           -----------------------------
> > rpc_kill_sb
> > sn->pipefs_sb = NULL                    rpc_release_client
> > (UMOUNT_EVENT)                          rpc_free_auth
> > rpc_pipefs_event
> > rpc_get_client_for_event
> > !atomic_inc_not_zero(cl_count)
> > <skip the client>
> >                                          atomic_inc(cl_count)
> >                                          rpc_free_client
> >                                          rpc_clnt_remove_pipedir
> >                                          <skip client dir removing>
> >
> > To fix this, this patch does the following:
> >
> > 1) Calls RPC_PIPEFS_UMOUNT notification with sn->pipefs_sb_lock being held.
> > 2) Removes SUNRPC client from the list AFTER pipes destroying.
> > 3) Doesn't hold RPC client on notification: if client in the list, then it
> > can't be destroyed while sn->pipefs_sb_lock in hold by notification caller.
> >
> > Signed-off-by: Stanislav Kinsbursky <skinsbursky@xxxxxxxxxxxxx>
> > Cc: stable@xxxxxxxxxxxxxxx
> > ---
> >   net/sunrpc/clnt.c     |    5 +----
> >   net/sunrpc/rpc_pipe.c |    2 +-
> >   2 files changed, 2 insertions(+), 5 deletions(-)
>
> <snip>
>
> > diff --git a/net/sunrpc/rpc_pipe.c b/net/sunrpc/rpc_pipe.c
> > index c512448..efca2f7 100644
> > --- a/net/sunrpc/rpc_pipe.c
> > +++ b/net/sunrpc/rpc_pipe.c
> > @@ -1165,7 +1165,6 @@ static void rpc_kill_sb(struct super_block *sb)
> >   		goto out;
> >   	}
> >   	sn->pipefs_sb = NULL;
> > -	mutex_unlock(&sn->pipefs_sb_lock);
> >   	dprintk("RPC:       sending pipefs UMOUNT notification for net %p%s\n",
> >   		net, NET_NAME(net));
> >   	blocking_notifier_call_chain(&rpc_pipefs_notifier_list,
> > @@ -1173,6 +1172,7 @@ static void rpc_kill_sb(struct super_block *sb)
> >   					   sb);
> >   	put_net(net);
> >   out:
> > +	mutex_unlock(&sn->pipefs_sb_lock);
>
> Is this safe to do after the put_net()?

Sure it's not. Sorry.
Will send the patch once more.

> >   	kill_litter_super(sb);
> >   }


--
Best regards,
Stanislav Kinsbursky
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