Re: NFSv4: Mounting NFS server which is down, blocks all other NFS mounts on same machine

[Trond Myklebust <trondmy@hammerspace.com>]

On Wed, 2021-06-09 at 10:31 -0400, Benjamin Coddington wrote:
> 
> It's not disputed that mounts waiting on the transport layer will block
> other mounts.
> 
> It might be able to be changed:  there's this torch:
> https://lore.kernel.org/linux-nfs/87378omld4.fsf@notabene.neil.brown.name/
> 

No.

> ..or there may be another way we don't have to wait ..
> 

OK. So let's look at how we can solve the problem of the initial
connection to the server timing out and causing hangs in
nfs41_walk_client_list(), and leave aside any other corner case
problems (such as the server going down while we're mounting).

How about something like the following (compile tested only) patch?

8<--------------------------------------------------------
From 30833f78b5b4c7780c91f705b0867ef5492a9eed Mon Sep 17 00:00:00 2001
From: Trond Myklebust <trond.myklebust@hammerspace.com>
Date: Wed, 9 Jun 2021 10:04:46 -0400
Subject: [PATCH] NFSv4: Initialise connection to the server in
 nfs4_alloc_client()

Set up the connection to the NFSv4 server in nfs4_alloc_client(), before
we've added the struct nfs_client to the net-namespace's nfs_client_list
so that a downed server won't cause other mounts to hang in the trunking
detection code.

Reported-by: Michael Wakabayashi <mwakabayashi@vmware.com>
Fixes: 5c6e5b60aae4 ("NFS: Fix an Oops in the pNFS files and flexfiles connection setup to the DS")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
---
 fs/nfs/nfs4client.c | 82 +++++++++++++++++++++++----------------------
 1 file changed, 42 insertions(+), 40 deletions(-)

diff --git a/fs/nfs/nfs4client.c b/fs/nfs/nfs4client.c
index 42719384e25f..28431acd1230 100644
--- a/fs/nfs/nfs4client.c
+++ b/fs/nfs/nfs4client.c
@@ -197,8 +197,11 @@ void nfs40_shutdown_client(struct nfs_client *clp)
 
 struct nfs_client *nfs4_alloc_client(const struct nfs_client_initdata *cl_init)
 {
-	int err;
+	char buf[INET6_ADDRSTRLEN + 1];
+	const char *ip_addr = cl_init->ip_addr;
 	struct nfs_client *clp = nfs_alloc_client(cl_init);
+	int err;
+
 	if (IS_ERR(clp))
 		return clp;
 
@@ -222,6 +225,44 @@ struct nfs_client *nfs4_alloc_client(const struct nfs_client_initdata *cl_init)
 	init_waitqueue_head(&clp->cl_lock_waitq);
 #endif
 	INIT_LIST_HEAD(&clp->pending_cb_stateids);
+
+	if (cl_init->minorversion != 0)
+		__set_bit(NFS_CS_INFINITE_SLOTS, &clp->cl_flags);
+	__set_bit(NFS_CS_DISCRTRY, &clp->cl_flags);
+	__set_bit(NFS_CS_NO_RETRANS_TIMEOUT, &clp->cl_flags);
+
+	/*
+	 * Set up the connection to the server before we add add to the
+	 * global list.
+	 */
+	err = nfs_create_rpc_client(clp, cl_init, RPC_AUTH_GSS_KRB5I);
+	if (err == -EINVAL)
+		err = nfs_create_rpc_client(clp, cl_init, RPC_AUTH_UNIX);
+	if (err < 0)
+		goto error;
+
+	/* If no clientaddr= option was specified, find a usable cb address */
+	if (ip_addr == NULL) {
+		struct sockaddr_storage cb_addr;
+		struct sockaddr *sap = (struct sockaddr *)&cb_addr;
+
+		err = rpc_localaddr(clp->cl_rpcclient, sap, sizeof(cb_addr));
+		if (err < 0)
+			goto error;
+		err = rpc_ntop(sap, buf, sizeof(buf));
+		if (err < 0)
+			goto error;
+		ip_addr = (const char *)buf;
+	}
+	strlcpy(clp->cl_ipaddr, ip_addr, sizeof(clp->cl_ipaddr));
+
+	err = nfs_idmap_new(clp);
+	if (err < 0) {
+		dprintk("%s: failed to create idmapper. Error = %d\n",
+			__func__, err);
+		goto error;
+	}
+	__set_bit(NFS_CS_IDMAP, &clp->cl_res_state);
 	return clp;
 
 error:
@@ -372,8 +413,6 @@ static int nfs4_init_client_minor_version(struct nfs_client *clp)
 struct nfs_client *nfs4_init_client(struct nfs_client *clp,
 				    const struct nfs_client_initdata *cl_init)
 {
-	char buf[INET6_ADDRSTRLEN + 1];
-	const char *ip_addr = cl_init->ip_addr;
 	struct nfs_client *old;
 	int error;
 
@@ -381,43 +420,6 @@ struct nfs_client *nfs4_init_client(struct nfs_client *clp,
 		/* the client is initialised already */
 		return clp;
 
-	/* Check NFS protocol revision and initialize RPC op vector */
-	clp->rpc_ops = &nfs_v4_clientops;
-
-	if (clp->cl_minorversion != 0)
-		__set_bit(NFS_CS_INFINITE_SLOTS, &clp->cl_flags);
-	__set_bit(NFS_CS_DISCRTRY, &clp->cl_flags);
-	__set_bit(NFS_CS_NO_RETRANS_TIMEOUT, &clp->cl_flags);
-
-	error = nfs_create_rpc_client(clp, cl_init, RPC_AUTH_GSS_KRB5I);
-	if (error == -EINVAL)
-		error = nfs_create_rpc_client(clp, cl_init, RPC_AUTH_UNIX);
-	if (error < 0)
-		goto error;
-
-	/* If no clientaddr= option was specified, find a usable cb address */
-	if (ip_addr == NULL) {
-		struct sockaddr_storage cb_addr;
-		struct sockaddr *sap = (struct sockaddr *)&cb_addr;
-
-		error = rpc_localaddr(clp->cl_rpcclient, sap, sizeof(cb_addr));
-		if (error < 0)
-			goto error;
-		error = rpc_ntop(sap, buf, sizeof(buf));
-		if (error < 0)
-			goto error;
-		ip_addr = (const char *)buf;
-	}
-	strlcpy(clp->cl_ipaddr, ip_addr, sizeof(clp->cl_ipaddr));
-
-	error = nfs_idmap_new(clp);
-	if (error < 0) {
-		dprintk("%s: failed to create idmapper. Error = %d\n",
-			__func__, error);
-		goto error;
-	}
-	__set_bit(NFS_CS_IDMAP, &clp->cl_res_state);
-
 	error = nfs4_init_client_minor_version(clp);
 	if (error < 0)
 		goto error;
-- 
2.31.1


-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com