Re: [PATCH] NFS: init client before declaration
From: Stanislav Kinsbursky
Date: Tue May 22 2012 - 12:18:25 EST
On 22.05.2012 19:51, Myklebust, Trond wrote:
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@xxxxxxxxxx>
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@xxxxxxxxxxxxx>
Signed-off-by: Trond Myklebust<Trond.Myklebust@xxxxxxxxxx>
---
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;
Ok, I see...
BTW, caller of this function is pipefs mount operation call... And when this
mount call waits for NFS clients - it look a bit odd to me...
+ 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);
We have another problem here.
nfs4_init_client() will try to create pipe dentries prior to set of NFS_CS_READY
to the client. And dentries will be created since semaphore is dropped and
per-net superblock variable is initialized already.
But __rpc_pipefs_event() relays on the fact, that no dentries present.
Looks like the problem was introduced by me in aad9487c...
So maybe we should not call "continue" instead "__rpc_pipefs_event()", when
client becomes ready?
Looks like this will allow us to handle such races.
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,
--
Best regards,
Stanislav Kinsbursky
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