linux-kernel - Re: [PATCH] NFS: init client before declaration

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Date:	Tue, 22 May 2012 15:51:44 +0000
From:	"Myklebust, Trond" <Trond.Myklebust@...app.com>
To:	Stanislav Kinsbursky <skinsbursky@...allels.com>
CC:	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...nvz.org" <devel@...nvz.org>
Subject: Re: [PATCH] NFS: init client before declaration

On Tue, 2012-05-22 at 19:29 +0400, Stanislav Kinsbursky wrote:
> On 22.05.2012 19:00, Myklebust, Trond wrote:
> > On Tue, 2012-05-22 at 10:29 -0400, Trond Myklebust wrote:
> >> On Tue, 2012-05-22 at 16:40 +0400, Stanislav Kinsbursky wrote:
> >>> Client have to be initialized prior to adding it to per-net clients list,
> >>> because otherwise there are races, shown below:
> >>>
> >>> CPU#0					CPU#1
> >>> _____					_____
> >>>
> >>> nfs_get_client
> >>> nfs_alloc_client
> >>> list_add(..., nfs_client_list)
> >>> 					rpc_fill_super
> >>> 					rpc_pipefs_event
> >>> 					nfs_get_client_for_event
> >>> 					__rpc_pipefs_event
> >>> 					(clp->cl_rpcclient is uninitialized)
> >>> 					BUG()
> >>> init_client
> >>> clp->cl_rpcclient = ...
> >>>
> >>
> >> Why not simply change nfs_get_client_for_event() so that it doesn't
> >> touch nfs_clients that have clp->cl_cons_state!=NFS_CS_READY?
> >>
> >> That should ensure that it doesn't touch nfs_clients that failed to
> >> initialise and/or are still in the process of being initialised.
> >
> > ...actually, come to think of it. Why not just add a helper function
> > "bool nfs_client_active(const struct nfs_client *clp)" to
> > fs/nfs/client.c that does a call to
> > 	wait_event_killable(nfs_client_active_wq, clp->cl_cons_state<  NFS_CS_INITING);
> > and checks the resulting value of clp->cl_cons_state?
> >
> 
> Sorry, but I don't understand the idea...
> Where are you proposing to call this function?
> In __rpc_pipefs_event() prior to dentries creatios?

See below:

8<----------------------------------------------------------------------------------
From f5b90df6381a20395d9f88a199e9e52f44267457 Mon Sep 17 00:00:00 2001
From: Trond Myklebust <Trond.Myklebust@...app.com>
Date: Tue, 22 May 2012 11:49:55 -0400
Subject: [PATCH] NFSv4: Fix a race in the net namespace mount notification

Since the struct nfs_client gets added to the global nfs_client_list
before it is initialised, it is possible that rpc_pipefs_event can
end up trying to create idmapper entries for such a thing.

The solution is to have the mount notification wait for the
nfs_client initialisation to complete.

Reported-by: Stanislav Kinsbursky <skinsbursky@...allels.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@...app.com>
---
 fs/nfs/client.c   |   14 ++++++++++++++
 fs/nfs/idmap.c    |    3 ++-
 fs/nfs/internal.h |    1 +
 3 files changed, 17 insertions(+), 1 deletions(-)

diff --git a/fs/nfs/client.c b/fs/nfs/client.c
index 60f7e4e..3fa44ef 100644
--- a/fs/nfs/client.c
+++ b/fs/nfs/client.c
@@ -592,6 +592,20 @@ void nfs_mark_client_ready(struct nfs_client *clp, int state)
 	wake_up_all(&nfs_client_active_wq);
 }
 
+static bool nfs_client_ready(struct nfs_client *clp)
+{
+	return clp->cl_cons_state <= NFS_CS_READY;
+}
+
+int nfs_wait_client_ready(struct nfs_client *clp)
+{
+	if (wait_event_killable(nfs_client_active_wq, nfs_client_ready(clp)) < 0)
+		return -ERESTARTSYS;
+	if (clp->cl_cons_state < 0)
+		return clp->cl_cons_state;
+	return 0;
+}
+
 /*
  * With sessions, the client is not marked ready until after a
  * successful EXCHANGE_ID and CREATE_SESSION.
diff --git a/fs/nfs/idmap.c b/fs/nfs/idmap.c
index 3e8edbe..67962c8 100644
--- a/fs/nfs/idmap.c
+++ b/fs/nfs/idmap.c
@@ -558,7 +558,8 @@ static int rpc_pipefs_event(struct notifier_block *nb, unsigned long event,
 		return 0;
 
 	while ((clp = nfs_get_client_for_event(sb->s_fs_info, event))) {
-		error = __rpc_pipefs_event(clp, event, sb);
+		if (nfs_wait_client_ready(clp) == 0)
+			error = __rpc_pipefs_event(clp, event, sb);
 		nfs_put_client(clp);
 		if (error)
 			break;
diff --git a/fs/nfs/internal.h b/fs/nfs/internal.h
index b777bda..3be00a0 100644
--- a/fs/nfs/internal.h
+++ b/fs/nfs/internal.h
@@ -168,6 +168,7 @@ extern struct nfs_server *nfs_clone_server(struct nfs_server *,
 					   struct nfs_fattr *,
 					   rpc_authflavor_t);
 extern void nfs_mark_client_ready(struct nfs_client *clp, int state);
+extern int nfs_wait_client_ready(struct nfs_client *clp);
 extern int nfs4_check_client_ready(struct nfs_client *clp);
 extern struct nfs_client *nfs4_set_ds_client(struct nfs_client* mds_clp,
 					     const struct sockaddr *ds_addr,
-- 
1.7.7.6


-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@...app.com
www.netapp.com