SUNRPC: PipeFS races fixes

PATCH Superseded Stanislav Kinsbursky 3 participants 9 messages Jun 24, 2013 – Jun 28, 2013

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Stanislav Kinsbursky

author

2013-06-24 07:52 UTC #0 lore raw

v3 cover SUNRPC: PipeFS races fixes

This series fixes races between PipeFS mount/umount notification calls and SUNRPC clients creation and destruction.

https://bugzilla.redhat.com/show_bug.cgi?id=924649

v3: fixes first (for easy backport to stable)

v2: Fixed few silly locking bugs.

The following series implements...

---

Stanislav Kinsbursky (4):
SUNRPC: fix races on PipeFS MOUNT notifications
SUNRPC: fix races on PipeFS UMOUNT notifications
SUNRPC: split client creation routine into setup and registration
SUNRPC: PipeFS MOUNT notification optimization for dying clients

 net/sunrpc/clnt.c     |   71 ++++++++++++++++++++++++++++++-------------------
 net/sunrpc/rpc_pipe.c |    5 +++
 2 files changed, 48 insertions(+), 28 deletions(-)

Stanislav Kinsbursky

author

2013-06-24 07:52 UTC #1 lore raw

PATCH v3 1/4 SUNRPC: fix races on PipeFS MOUNT notifications

Below are races, when RPC client can be created without PiepFS dentries

CPU#0 CPU#1
----------------------------- -----------------------------
rpc_new_client rpc_fill_super
rpc_setup_pipedir
mutex_lock(&sn->pipefs_sb_lock)
rpc_get_sb_net == NULL
(no per-net PipeFS superblock)

					sn->pipefs_sb = sb;
					notifier_call_chain(MOUNT)
					(client is not in the list)

rpc_register_client
(client without pipes dentries)

To fix this patch:
1) makes PipeFS mount notification call with pipefs_sb_lock being held.
2) releases pipefs_sb_lock on new SUNRPC client creation only after registration.

Signed-off-by Stanislav Kinsbursky <[email protected]>

Cc [email protected]

---
 net/sunrpc/clnt.c     |   26 +++++++++++++++-----------
 net/sunrpc/rpc_pipe.c |    3 +++
 2 files changed, 18 insertions(+), 11 deletions(-)

net/sunrpc/clnt.c +15 ~~-11~~

index 5a750b9..b827a4b 100644
@@ -157,20 +157,15 @@ static struct dentry *rpc_setup_pipedir_sb(struct super_block *sb,
 }
 
 static int
-rpc_setup_pipedir(struct rpc_clnt *clnt, const char *dir_name)
+rpc_setup_pipedir(struct rpc_clnt *clnt, const char *dir_name,
+		  struct super_block *pipefs_sb)
 {
-	struct net *net = rpc_net_ns(clnt);
-	struct super_block *pipefs_sb;
 	struct dentry *dentry;
 
 	clnt->cl_dentry = NULL;
 	if (dir_name == NULL)
 		return 0;
-	pipefs_sb = rpc_get_sb_net(net);
-	if (!pipefs_sb)
-		return 0;
 	dentry = rpc_setup_pipedir_sb(pipefs_sb, clnt, dir_name);
-	rpc_put_sb_net(net);
 	if (IS_ERR(dentry))
 		return PTR_ERR(dentry);
 	clnt->cl_dentry = dentry;

@@ -296,6 +291,7 @@ static struct rpc_clnt * rpc_new_client(const struct rpc_create_args *args, stru
 	struct rpc_clnt		*clnt = NULL;
 	struct rpc_auth		*auth;
 	int err;
+	struct super_block *pipefs_sb;
 
 	/* sanity check the name before trying to print it */
 	dprintk("RPC:       creating %s client for %s (xprt %p)\n",

@@ -354,9 +350,12 @@ static struct rpc_clnt * rpc_new_client(const struct rpc_create_args *args, stru
 
 	atomic_set(&clnt->cl_count, 1);
 
-	err = rpc_setup_pipedir(clnt, program->pipe_dir_name);
-	if (err < 0)
-		goto out_no_path;
+	pipefs_sb = rpc_get_sb_net(rpc_net_ns(clnt));
+	if (pipefs_sb) {
+		err = rpc_setup_pipedir(clnt, program->pipe_dir_name, pipefs_sb);
+		if (err)
+			goto out_no_path;
+	}
 
 	auth = rpcauth_create(args->authflavor, clnt);
 	if (IS_ERR(auth)) {

@@ -369,11 +368,16 @@ static struct rpc_clnt * rpc_new_client(const struct rpc_create_args *args, stru
 	/* save the nodename */
 	rpc_clnt_set_nodename(clnt, utsname()->nodename);
 	rpc_register_client(clnt);
+	if (pipefs_sb)
+		rpc_put_sb_net(rpc_net_ns(clnt));
 	return clnt;
 
 out_no_auth:
-	rpc_clnt_remove_pipedir(clnt);
+	if (pipefs_sb)
+		__rpc_clnt_remove_pipedir(clnt);
 out_no_path:
+	if (pipefs_sb)
+		rpc_put_sb_net(rpc_net_ns(clnt));
 	kfree(clnt->cl_principal);
 out_no_principal:
 	rpc_free_iostats(clnt->cl_metrics);

net/sunrpc/rpc_pipe.c +3 -0

index e7ce4b3..c512448 100644
@@ -1126,6 +1126,7 @@ rpc_fill_super(struct super_block *sb, void *data, int silent)
 		return -ENOMEM;
 	dprintk("RPC:       sending pipefs MOUNT notification for net %p%s\n",
 		net, NET_NAME(net));
+	mutex_lock(&sn->pipefs_sb_lock);
 	sn->pipefs_sb = sb;
 	err = blocking_notifier_call_chain(&rpc_pipefs_notifier_list,
 					   RPC_PIPEFS_MOUNT,

@@ -1133,6 +1134,7 @@ rpc_fill_super(struct super_block *sb, void *data, int silent)
 	if (err)
 		goto err_depopulate;
 	sb->s_fs_info = get_net(net);
+	mutex_unlock(&sn->pipefs_sb_lock);
 	return 0;
 
 err_depopulate:

@@ -1141,6 +1143,7 @@ err_depopulate:
 					   sb);
 	sn->pipefs_sb = NULL;
 	__rpc_depopulate(root, files, RPCAUTH_lockd, RPCAUTH_RootEOF);
+	mutex_unlock(&sn->pipefs_sb_lock);
 	return err;
 }

Stanislav Kinsbursky

author

2013-06-24 07:52 UTC #2 lore raw

PATCH v3 2/4 SUNRPC: fix races on PipeFS UMOUNT notifications

In reply to Stanislav Kinsbursky

CPU#0 CPU#1
----------------------------- -----------------------------
rpc_kill_sb
sn->pipefs_sb = NULL rpc_release_client
(UMOUNT_EVENT) rpc_free_auth
rpc_pipefs_event
rpc_get_client_for_event
!atomic_inc_not_zero(cl_count)
<skip the client>
atomic_inc(cl_count) rpc_free_client rpc_clnt_remove_pipedir <skip client dir removing>

To fix this, this patch does the following:

1) Calls RPC_PIPEFS_UMOUNT notification with sn->pipefs_sb_lock being held.
2) Removes SUNRPC client from the list AFTER pipes destroying.
3) Doesn't hold RPC client on notification: if client in the list, then it can't be destroyed while sn->pipefs_sb_lock in hold by notification caller.

Signed-off-by Stanislav Kinsbursky <[email protected]>

Cc [email protected]

---
 net/sunrpc/clnt.c     |    5 +----
 net/sunrpc/rpc_pipe.c |    2 +-
 2 files changed, 2 insertions(+), 5 deletions(-)

net/sunrpc/clnt.c +1 -4

index b827a4b..41f180c 100644
@@ -236,8 +236,6 @@ static struct rpc_clnt *rpc_get_client_for_event(struct net *net, int event)
 			continue;
 		if (rpc_clnt_skip_event(clnt, event))
 			continue;
-		if (atomic_inc_not_zero(&clnt->cl_count) == 0)
-			continue;
 		spin_unlock(&sn->rpc_client_lock);
 		return clnt;
 	}

@@ -254,7 +252,6 @@ static int rpc_pipefs_event(struct notifier_block *nb, unsigned long event,
 
 	while ((clnt = rpc_get_client_for_event(sb->s_fs_info, event))) {
 		error = __rpc_pipefs_event(clnt, event, sb);
-		rpc_release_client(clnt);
 		if (error)
 			break;
 	}

@@ -641,8 +638,8 @@ rpc_free_client(struct rpc_clnt *clnt)
 			rcu_dereference(clnt->cl_xprt)->servername);
 	if (clnt->cl_parent != clnt)
 		rpc_release_client(clnt->cl_parent);
-	rpc_unregister_client(clnt);
 	rpc_clnt_remove_pipedir(clnt);
+	rpc_unregister_client(clnt);
 	rpc_free_iostats(clnt->cl_metrics);
 	kfree(clnt->cl_principal);
 	clnt->cl_metrics = NULL;

net/sunrpc/rpc_pipe.c +1 -1

index c512448..efca2f7 100644
@@ -1165,7 +1165,6 @@ static void rpc_kill_sb(struct super_block *sb)
 		goto out;
 	}
 	sn->pipefs_sb = NULL;
-	mutex_unlock(&sn->pipefs_sb_lock);
 	dprintk("RPC:       sending pipefs UMOUNT notification for net %p%s\n",
 		net, NET_NAME(net));
 	blocking_notifier_call_chain(&rpc_pipefs_notifier_list,

@@ -1173,6 +1172,7 @@ static void rpc_kill_sb(struct super_block *sb)
 					   sb);
 	put_net(net);
 out:
+	mutex_unlock(&sn->pipefs_sb_lock);
 	kill_litter_super(sb);
 }

Myklebust, Trond

2013-06-25 16:13 UTC #3 lore raw

Re: [PATCH v3 2/4] SUNRPC: fix races on PipeFS UMOUNT notifications

Quoted 27 lines · Stanislav Kinsbursky

CPU#0 CPU#1
----------------------------- -----------------------------
rpc_kill_sb
sn->pipefs_sb = NULL rpc_release_client
(UMOUNT_EVENT) rpc_free_auth
rpc_pipefs_event
rpc_get_client_for_event
!atomic_inc_not_zero(cl_count)
<skip the client>
atomic_inc(cl_count) rpc_free_client rpc_clnt_remove_pipedir <skip client dir removing>
To fix this, this patch does the following:
1) Calls RPC_PIPEFS_UMOUNT notification with sn->pipefs_sb_lock being held.
2) Removes SUNRPC client from the list AFTER pipes destroying.
3) Doesn't hold RPC client on notification: if client in the list, then it can't be destroyed while sn->pipefs_sb_lock in hold by notification caller.
Signed-off-by Stanislav Kinsbursky <[email protected]>
Cc [email protected]
---
 net/sunrpc/clnt.c     |    5 +----
 net/sunrpc/rpc_pipe.c |    2 +-
 2 files changed, 2 insertions(+), 5 deletions(-)

<snip>

Quoted 13 lines

net/sunrpc/rpc_pipe.c +0 -1

index c512448..efca2f7 100644
@@ -1165,7 +1165,6 @@ static void rpc_kill_sb(struct super_block *sb)
 		goto out;
 	}
 	sn->pipefs_sb = NULL;
-	mutex_unlock(&sn->pipefs_sb_lock);
 	dprintk("RPC:       sending pipefs UMOUNT notification for net %p%s\n",
 		net, NET_NAME(net));
 	blocking_notifier_call_chain(&rpc_pipefs_notifier_list,

net/sunrpc/rpc_pipe.c static void rpc_kill_sb(struct super_block *sb) · line 1175

Quoted 4 lines

net/sunrpc/rpc_pipe.c +1 -0

@@ -1173,6 +1172,7 @@ static void rpc_kill_sb(struct super_block *sb)
 					   sb);
 	put_net(net);
 out:
+	mutex_unlock(&sn->pipefs_sb_lock);

Is this safe to do after the put_net()?

Quoted 4 lines

net/sunrpc/rpc_pipe.c +0 -0
 	kill_litter_super(sb);
 }
 

Signature · 6 lines

Trond Myklebust
Linux NFS client maintainer

NetApp
[email protected]
www.netapp.com

Stanislav Kinsbursky

author

2013-06-26 05:32 UTC #4 lore raw

Re: [PATCH v3 2/4] SUNRPC: fix races on PipeFS UMOUNT notifications

25.06.2013 20:13, Myklebust, Trond пишет:

Quoted 42 lines · Stanislav Kinsbursky

Quoted 27 lines
CPU#0 CPU#1
----------------------------- -----------------------------
rpc_kill_sb
sn->pipefs_sb = NULL rpc_release_client
(UMOUNT_EVENT) rpc_free_auth
rpc_pipefs_event
rpc_get_client_for_event
!atomic_inc_not_zero(cl_count)
<skip the client>
atomic_inc(cl_count) rpc_free_client rpc_clnt_remove_pipedir <skip client dir removing>
To fix this, this patch does the following:
1) Calls RPC_PIPEFS_UMOUNT notification with sn->pipefs_sb_lock being held.
2) Removes SUNRPC client from the list AFTER pipes destroying.
3) Doesn't hold RPC client on notification: if client in the list, then it can't be destroyed while sn->pipefs_sb_lock in hold by notification caller.
Signed-off-by Stanislav Kinsbursky <[email protected]>
Cc [email protected]
---
  net/sunrpc/clnt.c     |    5 +----
  net/sunrpc/rpc_pipe.c |    2 +-
  2 files changed, 2 insertions(+), 5 deletions(-)
<snip>
Quoted 11 lines
net/sunrpc/rpc_pipe.c +0 -1
index c512448..efca2f7 100644
@@ -1165,7 +1165,6 @@ static void rpc_kill_sb(struct super_block *sb)
  		goto out;
  	}
  	sn->pipefs_sb = NULL;
-	mutex_unlock(&sn->pipefs_sb_lock);
  	dprintk("RPC:       sending pipefs UMOUNT notification for net %p%s\n",
  		net, NET_NAME(net));

Quoted 9 lines

net/sunrpc/rpc_pipe.c static void rpc_kill_sb(struct super_block *sb) · line 1175
Quoted 6 lines
net/sunrpc/rpc_pipe.c +1 -0
  	blocking_notifier_call_chain(&rpc_pipefs_notifier_list,
@@ -1173,6 +1172,7 @@ static void rpc_kill_sb(struct super_block *sb)
  					   sb);
  	put_net(net);
  out:
+	mutex_unlock(&sn->pipefs_sb_lock);
Is this safe to do after the put_net()?

Sure it's not. Sorry.
Will send the patch once more.

Quoted 6 lines

Quoted 4 lines
net/sunrpc/rpc_pipe.c +0 -0
  	kill_litter_super(sb);
  }
 

Signature · 2 lines

Best regards,
Stanislav Kinsbursky

Stanislav Kinsbursky

author

2013-06-26 06:15 UTC #5 lore raw

PATCH v4 1/1 SUNRPC: fix races on PipeFS UMOUNT notifications

In reply to Stanislav Kinsbursky

To fix this, this patch does the following:

Signed-off-by Stanislav Kinsbursky <[email protected]>

Cc [email protected]

---
 net/sunrpc/clnt.c     |    5 +----
 net/sunrpc/rpc_pipe.c |    2 +-
 2 files changed, 2 insertions(+), 5 deletions(-)

net/sunrpc/clnt.c +1 -4

index b827a4b..41f180c 100644
@@ -236,8 +236,6 @@ static struct rpc_clnt *rpc_get_client_for_event(struct net *net, int event)
 			continue;
 		if (rpc_clnt_skip_event(clnt, event))
 			continue;
-		if (atomic_inc_not_zero(&clnt->cl_count) == 0)
-			continue;
 		spin_unlock(&sn->rpc_client_lock);
 		return clnt;
 	}

@@ -254,7 +252,6 @@ static int rpc_pipefs_event(struct notifier_block *nb, unsigned long event,
 
 	while ((clnt = rpc_get_client_for_event(sb->s_fs_info, event))) {
 		error = __rpc_pipefs_event(clnt, event, sb);
-		rpc_release_client(clnt);
 		if (error)
 			break;
 	}

@@ -641,8 +638,8 @@ rpc_free_client(struct rpc_clnt *clnt)
 			rcu_dereference(clnt->cl_xprt)->servername);
 	if (clnt->cl_parent != clnt)
 		rpc_release_client(clnt->cl_parent);
-	rpc_unregister_client(clnt);
 	rpc_clnt_remove_pipedir(clnt);
+	rpc_unregister_client(clnt);
 	rpc_free_iostats(clnt->cl_metrics);
 	kfree(clnt->cl_principal);
 	clnt->cl_metrics = NULL;

net/sunrpc/rpc_pipe.c +1 -1

index c512448..9b4ec5b 100644
@@ -1165,12 +1165,12 @@ static void rpc_kill_sb(struct super_block *sb)
 		goto out;
 	}
 	sn->pipefs_sb = NULL;
-	mutex_unlock(&sn->pipefs_sb_lock);
 	dprintk("RPC:       sending pipefs UMOUNT notification for net %p%s\n",
 		net, NET_NAME(net));
 	blocking_notifier_call_chain(&rpc_pipefs_notifier_list,
 					   RPC_PIPEFS_UMOUNT,
 					   sb);
+	mutex_unlock(&sn->pipefs_sb_lock);
 	put_net(net);
 out:
 	kill_litter_super(sb);

William Dauchy

2013-06-28 11:51 UTC #6 lore raw

Re: [PATCH v4] SUNRPC: fix races on PipeFS UMOUNT notifications

Quoted 39 lines · Stanislav Kinsbursky

net/sunrpc/clnt.c +1 -4

index b827a4b..41f180c 100644
@@ -236,8 +236,6 @@ static struct rpc_clnt *rpc_get_client_for_event(struct net *net, int event)
                        continue;
                if (rpc_clnt_skip_event(clnt, event))
                        continue;
-               if (atomic_inc_not_zero(&clnt->cl_count) == 0)
-                       continue;
                spin_unlock(&sn->rpc_client_lock);
                return clnt;
        }

@@ -254,7 +252,6 @@ static int rpc_pipefs_event(struct notifier_block *nb, unsigned long event,
 
        while ((clnt = rpc_get_client_for_event(sb->s_fs_info, event))) {
                error = __rpc_pipefs_event(clnt, event, sb);
-               rpc_release_client(clnt);
                if (error)
                        break;
        }

@@ -641,8 +638,8 @@ rpc_free_client(struct rpc_clnt *clnt)
                        rcu_dereference(clnt->cl_xprt)->servername);
        if (clnt->cl_parent != clnt)
                rpc_release_client(clnt->cl_parent);
-       rpc_unregister_client(clnt);
        rpc_clnt_remove_pipedir(clnt);
+       rpc_unregister_client(clnt);
        rpc_free_iostats(clnt->cl_metrics);
        kfree(clnt->cl_principal);
        clnt->cl_metrics = NULL;

net/sunrpc/rpc_pipe.c +0 -0

index c512448..9b4ec5b 100644
@@ -1165,12 +1165,12 @@ static void rpc_kill_sb(struct super_block *sb)
                goto out;
        }
        sn->pipefs_sb = NULL;

net/sunrpc/rpc_pipe.c static void rpc_kill_sb(struct super_block *sb) · line 1176

Quoted 10 lines

net/sunrpc/rpc_pipe.c +1 -1

-       mutex_unlock(&sn->pipefs_sb_lock);
        dprintk("RPC:       sending pipefs UMOUNT notification for net %p%s\n",
                net, NET_NAME(net));
        blocking_notifier_call_chain(&rpc_pipefs_notifier_list,
                                           RPC_PIPEFS_UMOUNT,
                                           sb);
+       mutex_unlock(&sn->pipefs_sb_lock);
        put_net(net);
 out:
        kill_litter_super(sb);

are these patches validated?
any chance to see them in tree soon? I wasn't able to find them on
http://git.linux-nfs.org/?p=trondmy/linux-nfs.git

Thanks,
--
William

Stanislav Kinsbursky

author

2013-06-24 07:53 UTC #7 lore raw

PATCH v3 3/4 SUNRPC: split client creation routine into setup and registration

In reply to Stanislav Kinsbursky

This helper moves all "registration" code to the new rpc_client_register() helper.
This helper will be used later in the series to synchronize against PipeFS MOUNT/UMOUNT events.

Signed-off-by Stanislav Kinsbursky <[email protected]>

---
 net/sunrpc/clnt.c |   64 ++++++++++++++++++++++++++++++++---------------------
 1 files changed, 39 insertions(+), 25 deletions(-)

net/sunrpc/clnt.c +39 ~~-25~~

index 41f180c..b4f1711 100644
@@ -281,14 +281,47 @@ static void rpc_clnt_set_nodename(struct rpc_clnt *clnt, const char *nodename)
 	memcpy(clnt->cl_nodename, nodename, clnt->cl_nodelen);
 }
 
+static int rpc_client_register(const struct rpc_create_args *args,
+			       struct rpc_clnt *clnt)
+{
+	const struct rpc_program *program = args->program;
+	struct rpc_auth *auth;
+	struct net *net = rpc_net_ns(clnt);
+	struct super_block *pipefs_sb;
+	int err = 0;
+
+	pipefs_sb = rpc_get_sb_net(net);
+	if (pipefs_sb) {
+		err = rpc_setup_pipedir(clnt, program->pipe_dir_name, pipefs_sb);
+		if (err)
+			goto out;
+	}
+
+	auth = rpcauth_create(args->authflavor, clnt);
+	if (IS_ERR(auth)) {
+		dprintk("RPC:       Couldn't create auth handle (flavor %u)\n",
+				args->authflavor);
+		err = PTR_ERR(auth);
+		goto err_auth;
+	}
+
+	rpc_register_client(clnt);
+out:
+	if (pipefs_sb)
+		rpc_put_sb_net(net);
+	return err;
+
+err_auth:
+	__rpc_clnt_remove_pipedir(clnt);
+	goto out;
+}
+
 static struct rpc_clnt * rpc_new_client(const struct rpc_create_args *args, struct rpc_xprt *xprt)
 {
 	const struct rpc_program *program = args->program;
 	const struct rpc_version *version;
 	struct rpc_clnt		*clnt = NULL;
-	struct rpc_auth		*auth;
 	int err;
-	struct super_block *pipefs_sb;
 
 	/* sanity check the name before trying to print it */
 	dprintk("RPC:       creating %s client for %s (xprt %p)\n",

@@ -347,34 +380,15 @@ static struct rpc_clnt * rpc_new_client(const struct rpc_create_args *args, stru
 
 	atomic_set(&clnt->cl_count, 1);
 
-	pipefs_sb = rpc_get_sb_net(rpc_net_ns(clnt));
-	if (pipefs_sb) {
-		err = rpc_setup_pipedir(clnt, program->pipe_dir_name, pipefs_sb);
-		if (err)
-			goto out_no_path;
-	}
-
-	auth = rpcauth_create(args->authflavor, clnt);
-	if (IS_ERR(auth)) {
-		dprintk("RPC:       Couldn't create auth handle (flavor %u)\n",
-				args->authflavor);
-		err = PTR_ERR(auth);
-		goto out_no_auth;
-	}
-
 	/* save the nodename */
 	rpc_clnt_set_nodename(clnt, utsname()->nodename);
-	rpc_register_client(clnt);
-	if (pipefs_sb)
-		rpc_put_sb_net(rpc_net_ns(clnt));
+
+	err = rpc_client_register(args, clnt);
+	if (err)
+		goto out_no_path;
 	return clnt;
 
-out_no_auth:
-	if (pipefs_sb)
-		__rpc_clnt_remove_pipedir(clnt);
 out_no_path:
-	if (pipefs_sb)
-		rpc_put_sb_net(rpc_net_ns(clnt));
 	kfree(clnt->cl_principal);
 out_no_principal:
 	rpc_free_iostats(clnt->cl_metrics);

Stanislav Kinsbursky

author

2013-06-24 07:53 UTC #8 lore raw

PATCH v3 4/4 SUNRPC: PipeFS MOUNT notification optimization for dying clients

In reply to Stanislav Kinsbursky

Not need to create pipes for dying client. So just skip them.

Note: we can safely dereference the client structure, because notification caller is holding sn->pipefs_sb_lock.

Signed-off-by Stanislav Kinsbursky <[email protected]>

Cc [email protected]

---
 net/sunrpc/clnt.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

net/sunrpc/clnt.c +2 -0

index b4f1711..f0339ae 100644
@@ -177,6 +177,8 @@ static inline int rpc_clnt_skip_event(struct rpc_clnt *clnt, unsigned long event
 	if (((event == RPC_PIPEFS_MOUNT) && clnt->cl_dentry) ||
 	    ((event == RPC_PIPEFS_UMOUNT) && !clnt->cl_dentry))
 		return 1;
+	if ((event == RPC_PIPEFS_MOUNT) && atomic_read(&clnt->cl_count) == 0)
+		return 1;
 	return 0;
 }