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

[Andrew Morton <akpm@osdl.org>]

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.