NFS: mount failure causes bad page state

While testing a kernel based upon ecd744ee
(with wrong boot arguments), I got the following bad page state entry while
NFS was trying to mount it's rootfs:

IP-Config: Complete:
      device=eth0, addr=192.168.1.101, mask=255.255.255.0, gw=255.255.255.255,
     host=192.168.1.101, domain=, nis-domain=(none),
     bootserver=192.168.1.100, rootserver=192.168.1.100, rootpath=
Looking up port of RPC 100003/2 on 192.168.1.100
rpcbind: server 192.168.1.100 not responding, timed out
Root-NFS: Unable to get nfsd port number from server, using default
Looking up port of RPC 100005/1 on 192.168.1.100
rpcbind: server 192.168.1.100 not responding, timed out
Root-NFS: Unable to get mountd port number from server, using default
mount: server 192.168.1.100 not responding, timed out
Root-NFS: Server returned error -5 while mounting /nfs/rootfs/
VFS: Unable to mount root fs via NFS, trying floppy.
Bad page state in process 'swapper'
page:c02b1260 flags:0x00000400 mapping:00000000 mapcount:0 count:0
Trying to fix it up, but a reboot is needed
Backtrace:
[<c0023e34>] (dump_stack+0x0/0x14) from [<c0062570>] (bad_page+0x70/0xac)
[<c0062500>] (bad_page+0x0/0xac) from [<c0064914>] (free_hot_cold_page+0x80/0x178)
[<c0064894>] (free_hot_cold_page+0x0/0x178) from [<c0064a74>] (free_hot_page+0x14/0x18)
[<c0064a60>] (free_hot_page+0x0/0x18) from [<c0067078>] (put_page+0xf8/0x154)
[<c0066f80>] (put_page+0x0/0x154) from [<c007dbc8>] (kfree+0xc8/0xd0)
[<c007db00>] (kfree+0x0/0xd0) from [<c00cbb54>] (nfs_get_sb+0x230/0x710)
[<c00cb924>] (nfs_get_sb+0x0/0x710) from [<c0084334>] (vfs_kern_mount+0x58/0xac)[<c00842dc>] (vfs_kern_mount+0x0/0xac) from [<c00843c0>] (do_kern_mount+0x38/0xf4)
[<c0084388>] (do_kern_mount+0x0/0xf4) from [<c0099c7c>] (do_mount+0x1e8/0x614)
...

This seems to be caused by use of an uninitialised structure due to NULL
options being passed to nfs_validate_mount_data().  Ensure that the
parsed mount data is always initialised.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
     (Trond: added fix for the same bug in nfs4_validate_mount_data()).
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/super.c

@@ -1054,10 +1054,11 @@ static int nfs_validate_mount_data(void *options,
 {
 	struct nfs_mount_data *data = (struct nfs_mount_data *)options;
 
+	memset(args, 0, sizeof(*args));
+
 	if (data == NULL)
 		goto out_no_data;
 
-	memset(args, 0, sizeof(*args));
 	args->flags		= (NFS_MOUNT_VER3 | NFS_MOUNT_TCP);
 	args->rsize		= NFS_MAX_FILE_IO_SIZE;
 	args->wsize		= NFS_MAX_FILE_IO_SIZE;
@@ -1536,10 +1537,11 @@ static int nfs4_validate_mount_data(void *options,
 	struct nfs4_mount_data *data = (struct nfs4_mount_data *)options;
 	char *c;
 
+	memset(args, 0, sizeof(*args));
+
 	if (data == NULL)
 		goto out_no_data;
 
-	memset(args, 0, sizeof(*args));
 	args->rsize		= NFS_MAX_FILE_IO_SIZE;
 	args->wsize		= NFS_MAX_FILE_IO_SIZE;
 	args->timeo		= 600;