NFS Client Bugfixes for Linux 5.4-rc6

Stable bugfixes:
 - Fix an RCU lock leak in nfs4_refresh_delegation_stateid()
 
 Other fixes:
 - The TCP back channel mustn't disappear while requests are outstanding
 - The RDMA back channel mustn't disappear while requests are outstanding
 - Destroy the back channel when we destroy the host transport
 - Don't allow a cached open with a revoked delegation
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Merge tag 'nfs-for-5.4-3' of git://git.linux-nfs.org/projects/anna/linux-nfs

Pull NFS client bugfixes from Anna Schumaker:
 "This contains two delegation fixes (with the RCU lock leak fix marked
  for stable), and three patches to fix destroying the the sunrpc back
  channel.

  Stable bugfixes:

   - Fix an RCU lock leak in nfs4_refresh_delegation_stateid()

  Other fixes:

   - The TCP back channel mustn't disappear while requests are
     outstanding

   - The RDMA back channel mustn't disappear while requests are
     outstanding

   - Destroy the back channel when we destroy the host transport

   - Don't allow a cached open with a revoked delegation"

* tag 'nfs-for-5.4-3' of git://git.linux-nfs.org/projects/anna/linux-nfs:
  NFS: Fix an RCU lock leak in nfs4_refresh_delegation_stateid()
  NFSv4: Don't allow a cached open with a revoked delegation
  SUNRPC: Destroy the back channel when we destroy the host transport
  SUNRPC: The RDMA back channel mustn't disappear while requests are outstanding
  SUNRPC: The TCP back channel mustn't disappear while requests are outstanding

fs/nfs/delegation.c

@@ -53,6 +53,16 @@ nfs4_is_valid_delegation(const struct nfs_delegation *delegation,
 	return false;
 }
 
+struct nfs_delegation *nfs4_get_valid_delegation(const struct inode *inode)
+{
+	struct nfs_delegation *delegation;
+
+	delegation = rcu_dereference(NFS_I(inode)->delegation);
+	if (nfs4_is_valid_delegation(delegation, 0))
+		return delegation;
+	return NULL;
+}
+
 static int
 nfs4_do_check_delegation(struct inode *inode, fmode_t flags, bool mark)
 {
@@ -1181,7 +1191,7 @@ bool nfs4_refresh_delegation_stateid(nfs4_stateid *dst, struct inode *inode)
 	if (delegation != NULL &&
 	    nfs4_stateid_match_other(dst, &delegation->stateid)) {
 		dst->seqid = delegation->stateid.seqid;
-		return ret;
+		ret = true;
 	}
 	rcu_read_unlock();
 out:

fs/nfs/delegation.h

@@ -68,6 +68,7 @@ int nfs4_lock_delegation_recall(struct file_lock *fl, struct nfs4_state *state,
 bool nfs4_copy_delegation_stateid(struct inode *inode, fmode_t flags, nfs4_stateid *dst, const struct cred **cred);
 bool nfs4_refresh_delegation_stateid(nfs4_stateid *dst, struct inode *inode);
 
+struct nfs_delegation *nfs4_get_valid_delegation(const struct inode *inode);
 void nfs_mark_delegation_referenced(struct nfs_delegation *delegation);
 int nfs4_have_delegation(struct inode *inode, fmode_t flags);
 int nfs4_check_delegation(struct inode *inode, fmode_t flags);

fs/nfs/nfs4proc.c

@@ -1440,8 +1440,6 @@ static int can_open_delegated(struct nfs_delegation *delegation, fmode_t fmode,
 		return 0;
 	if ((delegation->type & fmode) != fmode)
 		return 0;
-	if (test_bit(NFS_DELEGATION_RETURNING, &delegation->flags))
-		return 0;
 	switch (claim) {
 	case NFS4_OPEN_CLAIM_NULL:
 	case NFS4_OPEN_CLAIM_FH:
@@ -1810,7 +1808,6 @@ static void nfs4_return_incompatible_delegation(struct inode *inode, fmode_t fmo
 static struct nfs4_state *nfs4_try_open_cached(struct nfs4_opendata *opendata)
 {
 	struct nfs4_state *state = opendata->state;
-	struct nfs_inode *nfsi = NFS_I(state->inode);
 	struct nfs_delegation *delegation;
 	int open_mode = opendata->o_arg.open_flags;
 	fmode_t fmode = opendata->o_arg.fmode;
@@ -1827,7 +1824,7 @@ static struct nfs4_state *nfs4_try_open_cached(struct nfs4_opendata *opendata)
 		}
 		spin_unlock(&state->owner->so_lock);
 		rcu_read_lock();
-		delegation = rcu_dereference(nfsi->delegation);
+		delegation = nfs4_get_valid_delegation(state->inode);
 		if (!can_open_delegated(delegation, fmode, claim)) {
 			rcu_read_unlock();
 			break;
@@ -2371,7 +2368,7 @@ static void nfs4_open_prepare(struct rpc_task *task, void *calldata)
 					data->o_arg.open_flags, claim))
 			goto out_no_action;
 		rcu_read_lock();
-		delegation = rcu_dereference(NFS_I(data->state->inode)->delegation);
+		delegation = nfs4_get_valid_delegation(data->state->inode);
 		if (can_open_delegated(delegation, data->o_arg.fmode, claim))
 			goto unlock_no_action;
 		rcu_read_unlock();

include/linux/sunrpc/bc_xprt.h

@@ -64,6 +64,11 @@ static inline int xprt_setup_backchannel(struct rpc_xprt *xprt,
 	return 0;
 }
 
+static inline void xprt_destroy_backchannel(struct rpc_xprt *xprt,
+					    unsigned int max_reqs)
+{
+}
+
 static inline bool svc_is_backchannel(const struct svc_rqst *rqstp)
 {
 	return false;

net/sunrpc/backchannel_rqst.c

@@ -220,7 +220,7 @@ void xprt_destroy_bc(struct rpc_xprt *xprt, unsigned int max_reqs)
 		goto out;
 
 	spin_lock_bh(&xprt->bc_pa_lock);
-	xprt->bc_alloc_max -= max_reqs;
+	xprt->bc_alloc_max -= min(max_reqs, xprt->bc_alloc_max);
 	list_for_each_entry_safe(req, tmp, &xprt->bc_pa_list, rq_bc_pa_list) {
 		dprintk("RPC:        req=%p\n", req);
 		list_del(&req->rq_bc_pa_list);
@@ -307,8 +307,8 @@ void xprt_free_bc_rqst(struct rpc_rqst *req)
 		 */
 		dprintk("RPC:       Last session removed req=%p\n", req);
 		xprt_free_allocation(req);
-		return;
 	}
+	xprt_put(xprt);
 }
 
 /*
@@ -339,7 +339,7 @@ struct rpc_rqst *xprt_lookup_bc_request(struct rpc_xprt *xprt, __be32 xid)
 		spin_unlock(&xprt->bc_pa_lock);
 		if (new) {
 			if (req != new)
-				xprt_free_bc_rqst(new);
+				xprt_free_allocation(new);
 			break;
 		} else if (req)
 			break;
@@ -368,6 +368,7 @@ void xprt_complete_bc_request(struct rpc_rqst *req, uint32_t copied)
 	set_bit(RPC_BC_PA_IN_USE, &req->rq_bc_pa_state);
 
 	dprintk("RPC:       add callback request to list\n");
+	xprt_get(xprt);
 	spin_lock(&bc_serv->sv_cb_lock);
 	list_add(&req->rq_bc_list, &bc_serv->sv_cb_list);
 	wake_up(&bc_serv->sv_cb_waitq);

net/sunrpc/xprt.c

@@ -1942,6 +1942,11 @@ static void xprt_destroy_cb(struct work_struct *work)
 	rpc_destroy_wait_queue(&xprt->sending);
 	rpc_destroy_wait_queue(&xprt->backlog);
 	kfree(xprt->servername);
+	/*
+	 * Destroy any existing back channel
+	 */
+	xprt_destroy_backchannel(xprt, UINT_MAX);
+
 	/*
 	 * Tear down transport state and free the rpc_xprt
 	 */

net/sunrpc/xprtrdma/backchannel.c

@@ -163,6 +163,7 @@ void xprt_rdma_bc_free_rqst(struct rpc_rqst *rqst)
 	spin_lock(&xprt->bc_pa_lock);
 	list_add_tail(&rqst->rq_bc_pa_list, &xprt->bc_pa_list);
 	spin_unlock(&xprt->bc_pa_lock);
+	xprt_put(xprt);
 }
 
 static struct rpc_rqst *rpcrdma_bc_rqst_get(struct rpcrdma_xprt *r_xprt)
@@ -259,6 +260,7 @@ void rpcrdma_bc_receive_call(struct rpcrdma_xprt *r_xprt,
 
 	/* Queue rqst for ULP's callback service */
 	bc_serv = xprt->bc_serv;
+	xprt_get(xprt);
 	spin_lock(&bc_serv->sv_cb_lock);
 	list_add(&rqst->rq_bc_list, &bc_serv->sv_cb_list);
 	spin_unlock(&bc_serv->sv_cb_lock);