Re: [PATCH] Fix kernel lockup in RTL-8169 gigabit ethernet driver

[Manfred Spraul <manfred@colorfullife.com>]

Andrew wrote:

>The logic is faulty, or at least very odd.
>
>	tx_left = tp->cur_tx - dirty_tx;
>
>	while (tx_left > 0) {
>		int entry = dirty_tx % NUM_TX_DESC;
>
>		if (!(le32_to_cpu(tp->TxDescArray[entry].status) & OWNbit)) {
>			...
>		}
>	}
>
>Why is that `if' test there at all?  If it ever returns false, the box
>locks up.  A BUG_ON(le32_to_cpu(tp->TxDescArray[entry].status) & OWNbit)
>might make more sense.
>  
>
tx_left counts packets submitted by hard_xmit_start to the hardware. 
Initially OWNbit is set, the packet is owned by the nic. The OWNbit is 
cleared by the hardware after the packet was sent. A packet with OWNbit 
set means that the nic didn't send it yet to the wire. I think the "else 
break;" patch is correct, but someone with docs should confirm that.

Adam: did you see deadlocks that disappeared after applying your patch? 
It shouldn't deadlock - it should loop until the nic sends the packet to 
the wire. It might take a few msecs, but then it should continue. 
Perhaps gcc optimized away the reload from memory and loops on a 
register. Or there is another bug that is hidden by your patch.

--
    Manfred