On Tue, 2021-09-28 at 09:49 -0400, bfields@xxxxxxxxxxxx wrote: > On Tue, Sep 28, 2021 at 01:30:17PM +0000, Trond Myklebust wrote: > > On Tue, 2021-09-28 at 11:14 +0800, Wang Hai wrote: > > > When use-gss-proxy is set to 1, write_gssp() creates a rpc client > > > in > > > gssp_rpc_create(), this increases the netns refcount by 2, these > > > refcounts are supposed to be released in rpcsec_gss_exit_net(), > > > but > > > it > > > will never happen because rpcsec_gss_exit_net() is triggered only > > > when > > > the netns refcount gets to 0, specifically: > > > refcount=0 -> cleanup_net() -> ops_exit_list -> > > > rpcsec_gss_exit_net > > > It is a deadlock situation here, refcount will never get to 0 > > > unless > > > rpcsec_gss_exit_net() is called. So, in this case, the netns > > > refcount > > > should not be increased. > > > > > > In this case, xprt will take a netns refcount which is not > > > supposed > > > to be taken. Add a new flag to rpc_create_args called > > > RPC_CLNT_CREATE_NO_NET_REF for not increasing the netns refcount. > > > > > > It is safe not to hold the netns refcount, because when > > > cleanup_net(), it > > > will hold the gssp_lock and then shut down the rpc client > > > synchronously. > > > > > > > > I don't like this solution at all. Adding this kind of flag is > > going to > > lead to problems down the road. > > > > Is there any reason whatsoever why we need this RPC client to exist > > when there is no active knfsd server? IOW: Is there any reason why > > we > > shouldn't defer creating this RPC client for when knfsd starts up > > in > > this net namespace, and why we can't shut it down when knfsd shuts > > down? > > The rpc create is done in the context of the process that writes to > /proc/net/rpc/use-gss-proxy to get the right namespaces. I don't > know > how hard it would be capture that information for a later create. > svcauth_gss_proxy_init() uses the net namespace SVC_NET(rqstp) (i.e. the knfsd namespace) in the call to gssp_accept_sec_context_upcall(). IOW: the net namespace used in the call to find the RPC client is the one set up by knfsd, and so if use-gss-proxy was set in a different namespace than the one used by knfsd, then it won't be found. -- Trond Myklebust Linux NFS client maintainer, Hammerspace trond.myklebust@xxxxxxxxxxxxxxx
