On Wed, Mar 11, 2015 at 04:36:52PM +0100, Marc Kleine-Budde wrote: > On 03/11/2015 04:23 PM, Ahmed S. Darwish wrote: > > From: Ahmed S. Darwish <[email protected]> > > > > A number of tx queue wake-up events went missing due to the > > outlined scenario below. Start state is a pool of 16 tx URBs, > > active tx_urbs count = 15, with the netdev tx queue open. > > > > start_xmit() tx_acknowledge() > > ............ ................ > > atomic_inc(&tx_urbs); > > if (atomic_read(&tx_urbs) >= 16) { > > URB completion IRQ! > > --> > > atomic_dec(&tx_urbs); > > netif_wake_queue(); > > return; > > <-- > > end of IRQ! > > netif_stop_queue(); > > } > > > > At the end, the correct state expected is a 15 tx_urbs count > > value with the tx queue state _open_. Due to the race, we get > > the same tx_urbs value but with the tx queue state _stopped_. > > The wake-up event is completely lost. > > > > Thus avoid hand-rolled concurrency mechanisms and use a proper > > lock for contexts protection. > > I'm missing a spin_lock_init(), right? Please compile and test your code > with everything switch on in Kernel hacking -> Lock Debugging. >
Ouch... that passed through it seems since __ARCH_SPIN_LOCK_UNLOCKED is always zero on x86. Recompiling the kernel and re-iterating another patch series. Thanks, Darwish -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
