syzbot reported WARNING in rtl8150_start_xmit/usb_submit_urb.
This is the sequence of events that leads to the Warning:

    CPU0 (in rtl8150_start_xmit)   CPU1 (in rtl8150_start_xmit)    CPU2 (in rtl8150_set_multicast)
    netif_stop_queue();
                                                                    netif_stop_queue();
    usb_submit_urb();
                                                                    netif_wake_queue();  <-- Wakes up TX queue before it's ready
                                    netif_stop_queue();
                                    usb_submit_urb();                                    <-- Warning
	freeing urb

rtl8150_set_multicast is rtl8150's implementation of ndo_set_rx_mode and
should not be calling netif_stop_queue and notif_start_queue as these handle 
TX queue synchronization.

The net core function dev_set_rx_mode handles the synchronization
for rtl8150_set_multicast making it safe to remove these locks.

Reported-and-tested-by: syzbot+78cae3f37c62ad092caa@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=78cae3f37c62ad092caa
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: I Viswanath <redacted>
---
v2:
- Add explanation why netif_stop_queue/netif_wake_queue can be safely removed
- Add the net prefix to the patch, designating it to the net tree

Relevant logs:
[   65.779651][ T5648] About to enter stop queue ffff88805061e000, eth4
[   65.779664][ T5648] After stop queue ffff88805061e000, eth4
[   65.780296][ T5648] net eth4: eth name:eth4 SUBMIT: tx_urb=ffff888023219000, status=0, transfer_buffer_length=60, dev=ffff88805061ed80, netdev=ffff88805061e000, skb=ffff88804f907b80
[   65.790962][  T760] About to enter stop queue ffff88805061e000, eth4
[   65.790978][  T760] After stop queue ffff88805061e000, eth4
[   65.791874][  T760] net eth4: We are inside Multicast dev:ffff88805061ed80, netdev:ffff88805061e000
[   65.793259][  T760] About to enter netif_wake_queue ffff88805061e000, eth4
[   65.793264][  T760] After netif_wake_queue ffff88805061e000, eth4
[   65.822319][ T5829] About to enter stop queue ffff88805061e000, eth4
[   65.823135][ T5829] After stop queue ffff88805061e000, eth4
[   65.823739][ T5829] net eth4: eth name:eth4 SUBMIT: tx_urb=ffff888023219000, status=-115, transfer_buffer_length=90, dev=ffff88805061ed80, netdev=ffff88805061e000, skb=ffff88804b5363c0

 drivers/net/usb/rtl8150.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/net/usb/rtl8150.c b/drivers/net/usb/rtl8150.c
index ddff6f19ff98..92add3daadbb 100644
--- a/drivers/net/usb/rtl8150.c
+++ b/drivers/net/usb/rtl8150.c

@@ -664,7 +664,6 @@ static void rtl8150_set_multicast(struct net_device *netdev)
 	rtl8150_t *dev = netdev_priv(netdev);
 	u16 rx_creg = 0x9e;
 
-	netif_stop_queue(netdev);
 	if (netdev->flags & IFF_PROMISC) {
 		rx_creg |= 0x0001;
 		dev_info(&netdev->dev, "%s: promiscuous mode\n", netdev->name);

@@ -678,7 +677,6 @@ static void rtl8150_set_multicast(struct net_device *netdev)
 		rx_creg &= 0x00fc;
 	}
 	async_set_registers(dev, RCR, sizeof(rx_creg), rx_creg);
-	netif_wake_queue(netdev);
 }
 
 static netdev_tx_t rtl8150_start_xmit(struct sk_buff *skb,

-- 
2.47.3