atl1: fix oops when changing tx/rx ring params

Commit 3f5a2a713aad28480d86b0add00c68484b54febc zeroes out the statistics
message block (SMB) and coalescing message block (CMB) when adapter ring
resources are freed.  This is desirable behavior, but, as a side effect,
the commit leads to an oops when atl1_set_ringparam() attempts to alter
the number of rx or tx elements in the ring buffer (by using ethtool
-G, for example).  We don't want SMB or CMB to change during this
operation.

Modify atl1_set_ringparam() to preserve SMB and CMB when changing ring
parameters.

Cc: stable@kernel.org
Signed-off-by: Jay Cliburn <jcliburn@gmail.com>
Reported-by: Tõnu Raitviir <jussuf@linux.ee>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/atlx/atl1.c

@@ -3504,6 +3504,8 @@ static int atl1_set_ringparam(struct net_device *netdev,
 	struct atl1_rfd_ring rfd_old, rfd_new;
 	struct atl1_rrd_ring rrd_old, rrd_new;
 	struct atl1_ring_header rhdr_old, rhdr_new;
+	struct atl1_smb smb;
+	struct atl1_cmb cmb;
 	int err;
 
 	tpd_old = adapter->tpd_ring;
@@ -3544,11 +3546,19 @@ static int atl1_set_ringparam(struct net_device *netdev,
 		adapter->rrd_ring = rrd_old;
 		adapter->tpd_ring = tpd_old;
 		adapter->ring_header = rhdr_old;
+		/*
+		 * Save SMB and CMB, since atl1_free_ring_resources
+		 * will clear them.
+		 */
+		smb = adapter->smb;
+		cmb = adapter->cmb;
 		atl1_free_ring_resources(adapter);
 		adapter->rfd_ring = rfd_new;
 		adapter->rrd_ring = rrd_new;
 		adapter->tpd_ring = tpd_new;
 		adapter->ring_header = rhdr_new;
+		adapter->smb = smb;
+		adapter->cmb = cmb;
 
 		err = atl1_up(adapter);
 		if (err)