nfsd4: fix unlikely race in session replay case

In the replay case, the

	renew_client(session->se_client);

happens after we've droppped the sessionid_lock, and without holding a
reference on the session; so there's nothing preventing the session
being freed before we get here.

Thanks to Benny Halevy for catching a bug in an earlier version of this
patch.

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Acked-by: Benny Halevy <bhalevy@panasas.com>

1 files changed, 6 insertions, 4 deletions

diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index fb27b1db007b..05bc5bd63c95 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -3306,10 +3306,12 @@ nfs4svc_encode_compoundres(struct svc_rqst *rqstp, __be32 *p, struct nfsd4_compo
                 iov = &rqstp->rq_res.head[0];
         iov->iov_len = ((char*)resp->p) - (char*)iov->iov_base;
         BUG_ON(iov->iov_len > PAGE_SIZE);
-        if (nfsd4_has_session(cs) && cs->status != nfserr_replay_cache) {
-                nfsd4_store_cache_entry(resp);
-                dprintk("%s: SET SLOT STATE TO AVAILABLE\n", __func__);
-                resp->cstate.slot->sl_inuse = false;
+        if (nfsd4_has_session(cs)) {
+                if (cs->status != nfserr_replay_cache) {
+                        nfsd4_store_cache_entry(resp);
+                        dprintk("%s: SET SLOT STATE TO AVAILABLE\n", __func__);
+                        resp->cstate.slot->sl_inuse = false;
+                }
                 nfsd4_put_session(resp->cstate.session);
         }
         return 1;