net: systemport: Fix 64-bit stats deadlock

ffainelli · davem330 · commit 7095c973453e · 2017-09-15T14:24:10.000-07:00
We can enter a deadlock situation because there is no sufficient protection when ndo_get_stats64() runs in process context to guard against RX or TX NAPI contexts running in softirq, this can lead to the following lockdep splat and actual deadlock was experienced as well with an iperf session in the background and a while loop doing ifconfig + ethtool. [ 5.780350] ================================ [ 5.784679] WARNING: inconsistent lock state [ 5.789011] 4.13.0-rc7-02179-g32fae27c725d #70 Not tainted [ 5.794561] -------------------------------- [ 5.798890] inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage. [ 5.804971] swapper/0/0 [HC0[0]:SC1[1]:HE0:SE0] takes: [ 5.810175] (&syncp->seq#2){+.?...}, at: [<c0768a28>] bcm_sysport_tx_reclaim+0x30/0x54 [ 5.818327] {SOFTIRQ-ON-W} state was registered at: [ 5.823278] bcm_sysport_get_stats64+0x17c/0x258 [ 5.828053] dev_get_stats+0x38/0xac [ 5.831776] rtnl_fill_stats+0x30/0x118 [ 5.835761] rtnl_fill_ifinfo+0x538/0xe24 [ 5.839921] rtmsg_ifinfo_build_skb+0x6c/0xd8 [ 5.844430] rtmsg_ifinfo_event.part.5+0x14/0x44 [ 5.849201] rtmsg_ifinfo+0x20/0x28 [ 5.852837] register_netdevice+0x628/0x6b8 [ 5.857171] register_netdev+0x14/0x24 [ 5.861051] bcm_sysport_probe+0x30c/0x438 [ 5.865280] platform_drv_probe+0x50/0xb0 [ 5.869418] driver_probe_device+0x2e8/0x450 [ 5.873817] __driver_attach+0x104/0x120 [ 5.877871] bus_for_each_dev+0x7c/0xc0 [ 5.881834] bus_add_driver+0x1b0/0x270 [ 5.885797] driver_register+0x78/0xf4 [ 5.889675] do_one_initcall+0x54/0x190 [ 5.893646] kernel_init_freeable+0x144/0x1d0 [ 5.898135] kernel_init+0x8/0x110 [ 5.901665] ret_from_fork+0x14/0x2c [ 5.905363] irq event stamp: 24263 [ 5.908804] hardirqs last enabled at (24262): [<c08eecf0>] net_rx_action+0xc4/0x4e4 [ 5.916624] hardirqs last disabled at (24263): [<c0a7da00>] _raw_spin_lock_irqsave+0x1c/0x98 [ 5.925143] softirqs last enabled at (24258): [<c022a7fc>] irq_enter+0x84/0x98 [ 5.932524] softirqs last disabled at (24259): [<c022a918>] irq_exit+0x108/0x16c [ 5.939985] [ 5.939985] other info that might help us debug this: [ 5.946576] Possible unsafe locking scenario: [ 5.946576] [ 5.952556] CPU0 [ 5.955031] ---- [ 5.957506] lock(&syncp->seq#2); [ 5.960955] <Interrupt> [ 5.963604] lock(&syncp->seq#2); [ 5.967227] [ 5.967227] *** DEADLOCK *** [ 5.967227] [ 5.973222] 1 lock held by swapper/0/0: [ 5.977092] #0: (&(&ring->lock)->rlock){..-...}, at: [<c0768a18>] bcm_sysport_tx_reclaim+0x20/0x54 So just remove the u64_stats_update_begin()/end() pair in ndo_get_stats64() since it does not appear to be useful for anything. No inconsistency was observed with either ifconfig or ethtool, global TX counts equal the sum of per-queue TX counts on a 32-bit architecture. Fixes: 10377ba ("net: systemport: Support 64bit statistics") Signed-off-by: Florian Fainelli <f.fainelli@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/broadcom/bcmsysport.c b/drivers/net/ethernet/broadcom/bcmsysport.c
@@ -1735,11 +1735,8 @@ static void bcm_sysport_get_stats64(struct net_device *dev,
 		stats->tx_packets += tx_packets;
 	}
 
-	/* lockless update tx_bytes and tx_packets */
-	u64_stats_update_begin(&priv->syncp);
 	stats64->tx_bytes = stats->tx_bytes;
 	stats64->tx_packets = stats->tx_packets;
-	u64_stats_update_end(&priv->syncp);
 
 	do {
 		start = u64_stats_fetch_begin_irq(&priv->syncp);
