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

Andrew Morton
2004-04-03T10:07:52Z

Francois Romieu <romieu@fr.zoreil.com> wrote:
>
> Adam Nielsen <a.nielsen@optushome.com.au> :
> [...]
> > in the Realtek 8169 gigabit ethernet driver. Due to a logic error,
> > there is a loop in an interrupt handler that often goes infinite, thus
> > locking up the entire computer. The attached patch fixes the problem.
>
> - until there is an explanation on _why_ this condition happens, this is a
> band-aid for an unexplained condition, not a fix for a "logic error" (it
> may have interesting performance effects though);
>

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.