From: NeilBrown <neilb@suse.de>
Date: Fri, 22 Dec 2023 12:19:38 +1100
Subject: [PATCH] nfsd: drop st_mutex and rp_mutex before calling
 move_to_close_lru()
Patch-mainline: Submitted - 22dec2023 linux-nfs@vger.kernel.org
References: bsc#1217525

move_to_close_lru() is currently called with ->st_mutex and .rp_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 either
mutex.  These references will never be dropped so sc_count will never
reach 2.

There can be no harm in dropping ->st_mutex to 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.

Similarly dropping .rp_mutex is safe after the state is closed and so
no longer usable.  Another way to look at this is that nothing
significant happens between when nfsd4_close() now calls
nfsd4_cstate_clear_replay(), and where nfsd4_proc_compound calls
nfsd4_cstate_clear_replay() a little later.

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

Signed-off-by: NeilBrown <neilb@suse.de>
Acked-by: NeilBrown <neilb@suse.com>

---
 fs/nfsd/nfs4state.c |   12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -5456,7 +5456,7 @@ 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;
@@ -5470,11 +5470,11 @@ static void nfsd4_close_open_stateid(str
 			put_ol_stateid_locked(s, &reaplist);
 		spin_unlock(&clp->cl_lock);
 		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;
 	}
 }
 
@@ -5489,6 +5489,7 @@ nfsd4_close(struct svc_rqst *rqstp, stru
 	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);
@@ -5504,8 +5505,11 @@ nfsd4_close(struct svc_rqst *rqstp, stru
 	stp->st_stid.sc_type = NFS4_CLOSED_STID;
 	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);
+	nfsd4_cstate_clear_replay(cstate);
+	if (need_move_to_close_list)
+		move_to_close_lru(stp, net);
 
 	/* See RFC5661 sectionm 18.2.4 */
 	if (stp->st_stid.sc_client->cl_minorversion)