[PATCH] NFSv4: nfs4_state_manager() vs. nfs_server_remove_lists()

[Steve Dickson <steved@redhat.com>]

There is a race between nfs4_state_manager() and
nfs_server_remove_lists() that happens during a nfsv3 mount.

The v3 mount notices there is already a supper block so
nfs_server_remove_lists() called which uses the nfs_client_lock
spin lock to synchronize access to the client list.

At the same time nfs4_state_manager() is running through
the client list looking for work to do, using the same
lock. When nfs4_state_manager() wins the race to the
list, a v3 client pointer is found and not ignored
properly which causes the panic.

Moving some protocol checks before the state checking
avoids the panic.

CC: Stable Tree <stable@vger.kernel.org>
Signed-off-by: Steve Dickson <steved@redhat.com>
---
 fs/nfs/nfs4client.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/fs/nfs/nfs4client.c b/fs/nfs/nfs4client.c
index 53e435a..7ff4c02 100644
--- a/fs/nfs/nfs4client.c
+++ b/fs/nfs/nfs4client.c
@@ -622,6 +622,16 @@ int nfs41_walk_client_list(struct nfs_client *new,
 
 	spin_lock(&nn->nfs_client_lock);
 	list_for_each_entry(pos, &nn->nfs_client_list, cl_share_link) {
+
+		if (pos->rpc_ops != new->rpc_ops)
+			continue;
+
+		if (pos->cl_proto != new->cl_proto)
+			continue;
+
+		if (pos->cl_minorversion != new->cl_minorversion)
+			continue;
+
 		/* If "pos" isn't marked ready, we can't trust the
 		 * remaining fields in "pos", especially the client
 		 * ID and serverowner fields.  Wait for CREATE_SESSION
@@ -647,15 +657,6 @@ int nfs41_walk_client_list(struct nfs_client *new,
 		if (pos->cl_cons_state != NFS_CS_READY)
 			continue;
 
-		if (pos->rpc_ops != new->rpc_ops)
-			continue;
-
-		if (pos->cl_proto != new->cl_proto)
-			continue;
-
-		if (pos->cl_minorversion != new->cl_minorversion)
-			continue;
-
 		if (!nfs4_match_clientids(pos, new))
 			continue;
 
-- 
1.8.3.1