On Wed, Sep 22, 2021 at 03:16:34PM -0700, dai.ngo@xxxxxxxxxx wrote:
>
> On 9/22/21 2:14 PM, J. Bruce Fields wrote:
> >On Thu, Sep 16, 2021 at 02:22:11PM -0400, Dai Ngo wrote:
> >>+/*
> >>+ * If the conflict happens due to a NFSv4 request then check for
> >>+ * courtesy client and set rq_conflict_client so that upper layer
> >>+ * can destroy the conflict client and retry the call.
> >>+ */
> >>+static bool
> >>+nfsd_check_courtesy_client(struct nfs4_delegation *dp)
> >>+{
> >>+ struct svc_rqst *rqst;
> >>+ struct nfs4_client *clp = dp->dl_recall.cb_clp;
> >>+ struct nfsd_net *nn = net_generic(clp->net, nfsd_net_id);
> >>+ bool ret = false;
> >>+
> >>+ if (!i_am_nfsd()) {
> >>+ if (test_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags)) {
> >>+ set_bit(NFSD4_DESTROY_COURTESY_CLIENT, &clp->cl_flags);
> >>+ mod_delayed_work(laundry_wq, &nn->laundromat_work, 0);
> >>+ return true;
> >>+ }
> >>+ return false;
> >>+ }
> >>+ rqst = kthread_data(current);
> >>+ if (rqst->rq_prog != NFS_PROGRAM || rqst->rq_vers < 4)
> >>+ return false;
> >>+ rqst->rq_conflict_client = NULL;
> >>+
> >>+ spin_lock(&nn->client_lock);
> >>+ if (test_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags) &&
> >>+ !mark_client_expired_locked(clp)) {
> >>+ rqst->rq_conflict_client = clp;
> >>+ ret = true;
> >>+ }
> >>+ spin_unlock(&nn->client_lock);
> >Check whether this is safe; I think the flc_lock may be taken inside of
> >this lock elsewhere, resulting in a potential deadlock?
> >
> >rqst doesn't need any locking as it's only being used by this thread, so
> >it's the client expiration stuff that's the problem, I guess.
>
> mark_client_expired_locked needs to acquire cl_lock. I think the lock
> ordering is ok, client_lock -> cl_lock. nfsd4_exchange_id uses this
> lock ordering.
It's flc_lock (see locks.c) that I'm worried about. I've got a lockdep
warning here, taking a closer look....
nfsd4_release_lockowner takes clp->cl_lock and then fcl_lock.
Here we're taking fcl_lock and then client_lock.
As you say, elsewhere client_lock is taken and then cl_lock.
So that's the loop, I think.
--b.
