nfsd: drop st_mutex before calling move_to_close_lru()

move_to_close_lru() is currently called with ->st_mutex held.
This can lead to a deadlock as move_to_close_lru() waits for sc_count to
drop to 2, and some threads holding a reference might be waiting for the
mutex.  These references will never be dropped so sc_count will never
reach 2.

There can be no harm in dropping ->st_mutex before
move_to_close_lru() because the only place that takes the mutex is
nfsd4_lock_ol_stateid(), and it quickly aborts if sc_type is
NFS4_CLOSED_STID, which it will be before move_to_close_lru() is called.

See also
 https://lore.kernel.org/lkml/4dd1fe21e11344e5969bb112e954affb@jd.com/T/
where this problem was raised but not successfully resolved.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index e91e741719a0234b45c23fb94018fae9c939f11a..df07202cc53eb69520d5fa8fe69fd1f9228f5e48 100644 (file)
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -7357,7 +7357,7 @@ out:
        return status;
 }
 
-static void nfsd4_close_open_stateid(struct nfs4_ol_stateid *s)
+static bool nfsd4_close_open_stateid(struct nfs4_ol_stateid *s)
 {
        struct nfs4_client *clp = s->st_stid.sc_client;
        bool unhashed;
@@ -7374,11 +7374,11 @@ static void nfsd4_close_open_stateid(struct nfs4_ol_stateid *s)
                list_for_each_entry(stp, &reaplist, st_locks)
                        nfs4_free_cpntf_statelist(clp->net, &stp->st_stid);
                free_ol_stateid_reaplist(&reaplist);
+               return false;
        } else {
                spin_unlock(&clp->cl_lock);
                free_ol_stateid_reaplist(&reaplist);
-               if (unhashed)
-                       move_to_close_lru(s, clp->net);
+               return unhashed;
        }
 }
 
@@ -7394,6 +7394,7 @@ nfsd4_close(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
        struct nfs4_ol_stateid *stp;
        struct net *net = SVC_NET(rqstp);
        struct nfsd_net *nn = net_generic(net, nfsd_net_id);
+       bool need_move_to_close_list;
 
        dprintk("NFSD: nfsd4_close on file %pd\n",
                        cstate->current_fh.fh_dentry);
@@ -7418,8 +7419,10 @@ nfsd4_close(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
         */
        nfs4_inc_and_copy_stateid(&close->cl_stateid, &stp->st_stid);
 
-       nfsd4_close_open_stateid(stp);
+       need_move_to_close_list = nfsd4_close_open_stateid(stp);
        mutex_unlock(&stp->st_mutex);
+       if (need_move_to_close_list)
+               move_to_close_lru(stp, net);
 
        /* v4.1+ suggests that we send a special stateid in here, since the
         * clients should just ignore this anyway. Since this is not useful