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

Manfred Spraul
2004-04-03T11:30:48Z

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